SINGLE-LENS STEREOSCOPIC LIGHT-VALVES AND APPARATUSES

Abstract: The present invention is directed to a variety of stereoscopic optical systems and methods. In one configuration, an optical system includes a polarizer (1), a half-wave retarder (3), a polarization rotator (4), and an analyzing polarizer (2). Various configurations include first, second, and third encoding means, a micropolarizer and an array or matrix of filters for processing optical signals before receipt by an image acquisition system, encoding means located upstream of the object to be images, and first and second encoding means that each encode a different characteristic of an optical signal.

Description: SINGLE-LENS STEREOSCOPIC LIGHT- VALVES AND APPARATUSES FIELD OF THE INVENTION The present invention relates generally to a system and method for producing stereoscopic images and specifically to a system and method for producing stereoscopic images with a single lens that can be used in microscopes, endoscopes, video devices, photographic devices, and the like. BACKGROUND OF THE INVENTION Stereoscopic imaging is useful in a broad variety of applications and devices, such as microscopes, endoscopes, video devices, photographic devices, to name but a few. Generally, stereoscopic images are produced by dividing light reflected by or transmitted through the object into two parts or images of the object, e.g., left and right eye views. The two parts or images, when viewed by a viewer, will produce a three-dimensional image of the object as each eye will see a different image of the object. The images can be viewed simultaneously as with two oculars, or sequentially, as with video, to provide the three- dimensional image. There are several techniques used to divide reflected or transmitted light into two parts or images for the creation of a stereoscopic image. In one approach, passive mirrors or reflectors are used to divide the light. Examples of systems using this approach are described in U.S. Patents 2,639,653 to Fischer and 5,539,572 to Greenberg et al. In another approach, an active shutter-type mechanism is used to switch alternatively between light transmissive and opaque states to create a series of discrete images of the object. Examples of such systems are described in U.S. Patents 5,471,237 to Shipp and 5,828,487 to Greening et al. In yet another approach, complementary anaglyphic or color filters are used to create discrete light segments having differing wavelength bands. Examples of such systems include U.S. Patents 3,712,199 to Songer; 4,072,967 to Dudley; 4,290,675 to Beiser; 4,862,873 to Yajima et al; 5,706,128 to Greenberg; 5,751,341 to Chaleki et al.; and 5,867,312 to Greenberg. In a further approach, complementary polarizing filters are used to provide discrete light segments having differing polarization orientations. Examples of such systems include U.S. Patents 2,255,631 to Shulman; 4,072,967 to Dudley; 4,761,066 to Carter;5,706,128 to Greenberg; 5,592,328 to Greenberg; 5,964,696 to Mihalca et al.; and 5,867,312 to Greenberg. These approaches and/or systems can suffer from a number of drawbacks. These problems include limited magnification powers; alignment problems; distortion and visual noise from contaminants, keystoning, ghosting, double-image distortions, vignetting, etc. ; reduced stereoscopic information as magnification is increased; viewer discomfort due for example to visual misalignment; reliability, performance, and maintenance problems due to the use of active rather than passive devices; the use of costly components; a limited ability to acquire images of objects that impact polarization such as the sky, water, or reflecting surfaces; high optical losses due to the use of multiple holes to divide the light into discrete images; loss of certain wavelengths of light; and complexity of use. SUMMARY OF THE INVENTION The present invention generally produces a 3D effect by encoding an imaging signal to isolate or otherwise acquire portions of the imaging signal that correspond to depth information (i.e., in the Z-direction) as well as length and width information (i.e., in the X- and Y-directions) regarding an object reflecting or transmitting the imaging signal. As used herein, "encoding" means causing a differentiation between signal portions passing (typically simultaneously) through a defined spatial area. This is typically performed using one or more encoders that occlude and/or retard and/or alter a characteristic of one image signal portion relative to another image signal portion. In one configuration, encoding is performed by altering the signal so that the perceived out-of-focus areas of the reconstructed image differ between the background and foreground and/or between the left eye and right eye views. For example, in light-based imaging signals polarization is one method used as the basis for encoding the signal portions and thus producing the perceivable difference. In that event, the two signal portions have transversely oriented (typically orthogonal) polarization orientations. The imaging signal can be in the form of radiant energy (with a wavelength range of from about 400 nm. to about 800 nm. being typical). The radiant energy can be in the form of light energy, and can additionally be thermal energy, sound energy, electromagnetic energy, x-ray energy, fluid energy, particle energy, and any energy with cyclic or wavelike properties that can be focused to produce an aperture stop or the equivalent of an aperture stop. In one application, a 3D effect is obtained by dividing an out-of-focus portion of the imaging signal into discrete signal portions using an encoding device such as a filter. When light is the imaging signal for example, out-of-focus foreground points and out-of-focus background points typically (but not always) produce a circle of confusion on an imaging plane. The size of the circle of confusion relates directly to the distance of the background or foreground point behind or before the point in focus on the imaging plane. Stated another way, the diameter of the circle of confusion, as it increases, conveys information about the depth of that point relative to the image plane (i.e., the circle grows larger the further the point is from the image plane). The circle of confusion thus contains depth information that can be acquired to yield a 3D image. In one configuration, the background out-of-focus portion of the imaging signal is reversed and inverted from the foreground out-of-focus portion of the imaging signal. In one embodiment, a system is provided for producing a three-dimensional image of an object from an imaging signal containing imaging information relating to the object that includes: (a) first encoding means for encoding the imaging signal to produce an encoded imaging signal; and (b) second encoding means for encoding further a first portion of the encoded imaging signal but not a second portion of the encoded imaging signal. The further encoded first portion of the encoded imaging signal has a characteristic different from the second portion of the encoded imaging signal. The characteristic is typically polarization orientation, intensity, and/or wavelength distribution. The first and second imaging signal portions typically follow, have, or define a common optical path to reduce loss of signal energy relative to a system using multiple optical paths. The first and second filtering means are typically at least substantially orthogonal to the optical path. The imaging signal and/or first and second imaging signal portions are typically not collimated. The present invention can have many benefits relative to the prior art. Unlike the traditional approach for producing 3D effects, which uses two lenses in a parallactic displacement, the technique of the present invention does not suffer from parallactic displacement which often leads to keystoning, double image distortions, optical cross-talk, and/or ambiguous border information. Aperture encoded depth information contains a full core of information and avoids eye strain or viewer discomfort. The use of passive components reduces or eliminates maintenance (such as readjustment) and prolongs the useful life of the imaging device. The use of an encoding means at the aperture stop to encode only a portion of the signal permits the photographing of the sky, water, or reflecting surfaces that otherwise may affect polarization. The present invention can use internal polarization hardware that reduces (relative to systems using external polarization hardware) cost and complexity. The present invention can use a single as opposed to multiple lenses which is particularly advantageous in camera systems. The first and second encoding means can be any number of active and/or passive encoding devices. Passive elements are preferred, as active elements can be more costly to install and maintain and, when they fail, significantly degrade the optical properties and performance of the system. Examples include a polarizing (plane or circular) filter, a color (e.g., chromatic) or a non-color (e.g., an achromatic) filter, an occluder (a passive device that primarily reduces image signal intensity), a retarder (or phase shifter), a reflector or mirror (such as a prism, beam splitter, etc.), and a shutter (an active device that variably and/or controllably occludes all, some, or none of the image signal). The first and second encoding devices can be combined in any number of configurations. In one configuration, a linear or plane polarizer is followed by a half-wave retarder (that typically occupies only a portion (typically one-half) of the aperture stop). The linear polarizers are preferably not located near an image plane to avoid distortion and visual noise from contaminants. In another configuration, a linear or plane polarizer is followed by two-quarter wave retarders. In another configuration, a pair of opposing (or complementary) linear polarizing filters (e.g., orthogonal polarization filters) is followed by a half-wave retarder. In another configuration, a pair of opposing (or complementary) circular polarizers is followed by a half wave retarder. The use of circular polarizers relaxes alignment requirements when the oculars rotate as when adjusting interocular distance. In another configuration, a color filter (chromatic or achromatic) is followed by one or more active shutters (such as a liquid crystal shutter, mechanical shutter, etc,) or one or more reflectors or mirrors (such as a prism, beam splitter, etc.). In another configuration, a pair of color (e.g., anaglyphic, chromatic, or achromatic) filters (typically complementary) is followed by one or more active shutters (such as a liquid crystal shutter, mechanical shutter, etc,) or one or more reflectors or mirrors (e.g., a prism such as a beam splitter, etc.). The second encoding means is typically positioned at or near the aperture stop (and/or a conjugate thereof) to prevent the device from impairing or adding noise to the imaging signal. As used herein, an "aperture stop" or "aperture stop plane" of a lens system limits the size of the axial cone of energy which is accepted from object space and transferred to image space. It is a property of the aperture stop that all light emanating from a point in three-dimensional object space and accepted by the lens system generally fills the aperture stop; that is, the resultant image in image space within the imaging system is made up of an approximately even distribution of rays which have traveled equally throughout the entire area of the aperture stop. The entire optical path of a collimated beam of energy is a continuous aperture stop. In contrast, an uncollimated beam of energy typically has one or more discrete (spaced apart) aperture stops. Typically, the second encoding means is positioned within a distance of the aperture stop of no more than about one aperture stop diameter; more typically within a distance of the aperture stop of no more than about 75% of the aperture stop diameter; and even more typically within a distance of the aperture stop of no more than about 50% of the aperture stop diameter. In most applications, the first encoding means encodes a different (a greater) amount of the imaging signal when compared to the amount of the imaging signal encoded by the second encoding means; that is, the frontal area of the first encoding means is typically different (greater than) the frontal area of the second encoding means. The first encoding means typically encodes at least about 25%; more typically at least about 50% of the imaging signal, and even more typically at least substantially all of the imaging signal. By comparison, the second encoding means typically encodes less than all, more typically at least about 25% and no more than about 75%, and even more typically at least about 35% and no more than about 65% of the encoded imaging signal; that is, the second encoding means typically occupies from about 25% to about 75% and more typically from about 35% to about 65% of the aperture stop area. The second encoding means is typically positioned and sized to encode approximately one-half of the imaging signal passing the second encoding means. In another embodiment, one or more (analyzing) filtering means, such as one or more linear or planar polarizing filters, a reflector or mirror (e.g., a polarizing beam splitter), one or more achromatic filters, an occluder, and a shutter (e.g., a polarization rotator, a rotating polarizer, etc.) is placed after the foregoing components in the optical path of the imaging signal, enabling reverse stereo, non-stereo, true-stereo, and still photographs. A polarization rotator and the final linear polarizing filter can be used in conjunction with a modified objective lens to produce a video image. In one configuration, the analyzing filtering means has a parallel or orthogonal polarization orientation to a leading linear polarizer. In one configuration, each analyzing filtering means has a polarization orientation at least substantially parallel to a polarization orientation of a portion of the imaging signal to be filtered or encoded by the filtering means and therefore to the closest upstream encoding means that imparted, isolated, or filtered the polarization orientation to the imaging signal portion. In another embodiment, the (typically orthogonal) encoded imaging signal components are sequentially and alternatively passed through a switching means to enable any video or motion picture camera to record frame-sequential stereo images. Examples of switching means include a shutter such as a circular polarization rotator, a plane polarization rotator, a rotating circular polarizer, a rotating plane polarizer, a variable retarder, and/or a switched occluder. When light is the imaging signal and the switching means is a plane polarization rotator, such as an electric switched quarter-wave retarder (e.g., a liquid crystal switch that is part of a Ferro-Electric Liquid Crystal switch (FLC or FELC), a rotating polarizer, or a Pi cell), for example, the polarization rotator variably and controllably rotates the polarization of the first and second imaging signal portions. In one configuration, the rotation device has an unpowered state in which the device has a neutral effect on polarization and a powered state in which the device rotates the orientation of the imaging signal portions by a predetermined angle and permits light having only a specific polarization orientation to pass through the device. In this manner, discrete first and second image signal portions are alternately contacted with the image plane. In the event that the device malfunctions, the unpowered state will be used and the rotation device will only affect the loss of 3D information, not the loss of the 2D image signal. The polarization rotator can be anywhere in the light path between the first and last (analyzing) filtering means. In one operational mode, the polarization orientation of the rotating device preferably approximately parallels or is approximately orthogonal to that of the first (and/or second) encoding means. In one operational mode, the polarization rotator has a polarization orientation that is substantially parallel or orthogonal to a joint or an edge of the second encoding means. The techniques and devices of the present invention can be used not only with linear or plane polarization but also with circular polarization. In another embodiment, a relay lens system (typically having a plurality of lenses) is used to produce a conjugate of an aperture stop and re-project the image in the imaging signal onto a new image plane. The relay lens system can be used in an adapter that is mountable on a camera, endoscope, microscope, etc., to produce a conjugate of an aperture stop. In one configuration, an encoding filter placed at the created aperture stop alternately exposes each side of that aperture stop for imaging. In one configuration, the same or another encoding filter, such as a neutral density filter, can be positioned between lenses of adjacent relay lens systems. The filter can occlude a portion of the conjugate of the aperture stop to block passage of a portion of the imaging signal. A source signal can be encoded before or after the object being imaged to produce the imaging signal. In that event, the imaging signal (i.e., the signal after reflecting off of or passing through the object) may or may not be processed further by the devices described above. This technique produces similar results to a technique in which the imaging signal is processed only after reflecting off of or passing through the object. The components used to encode the source signal before the source signal contact the object are one or more of the devices and/or device configurations set forth above. In an exemplary embodiment of this approach, a system is provided for producing a three-dimensional image of an object from a signal to be reflected by or transmitted through the object that includes: (a) first encoding means for encoding the signal to produce an encoded imaging signal, wherein at least substantially all of the encoded imaging signal has a common polarization orientation and (b) second encoding means for further encoding a first portion of the encoded signal but not a second portion of the encoded signal, wherein the further encoded first portion has a polarization orientation transverse to the polarization orientation of the second portion. The first and second portions are then contacted with the object to be imaged. The system can further include one or more analyzing encoders positioned in the optical path downstream of the first and second encoding means and either before or after the object. In another exemplary embodiment of this approach, a method is provided that includes the steps of: (a) encoding a signal to produce an encoded imaging signal, wherein less than half or substantially all of the encoded imaging signal has a common polarization orientation; (b) contacting the first and second portions with an object to be imaged to form an imaging signal; and (c) encoding further the imaging signal. The encoders in steps (a) and (b) are located on opposing sides of the optical path relative to the position of the object. Polarized energy is passed through the object to reduce distortion and increase the perceptibility of the perceived image. In another embodiment, a system is provided for producing a three-dimensional image of an object from an imaging signal containing imaging information relating to the object that includes: (a) at least one image acquisition means for acquiring an image of an object from an imaging signal, the at least one image acquisition means having a matrix or array of imaging pixels; and (b) at least one matrix or array of filtering means corresponding to the at least one image acquisition means, located between the corresponding at least one image acquisition means and the object, for filtering (encoding) typically based on polarity, wavelength, or intensity, the imaging signal portions before receipt by the corresponding matrix or array of imaging pixels. The imaging acquisition means can be any suitable device for acquiring, generating, or producing an image from the imaging signal. Typically, the image acquisition means is a CCD and/or CMOS. The number of pixels and filtering means can be the same or different and can be of any magnitude. Typically, the number of filtering means is the same as the number of imaging pixels in the image acquisition means. The filtering means can be any suitable encoding means, such as a polarizing filter, an anaglyphic filter, a retarder, an occluder, and/or a shutter. The array or matrix of filtering means, also when composed of polarizing filters and is referred to as a micropolarizer, contains the filtering means laid out or configured in a predetermined order to produce a signal having a plurality of signal portions and segments with differing polarization orientations, wavelength distributions or intensities. The filtering means can be located in a spaced array or matrix in which adjacent filtering means are separated by a space. In this configuration, each filtering means in the matrix may remove substantially the same components of the imaging signal and/or have substantially the same impact on corresponding image signal segments. The difference in signal portions is caused by some signal portions being filtered or encoded and some passing unfiltered or unencoded through the space(s) between the filtering means. Conversely, the adjacent filtering means can be located in a dense array or matrix in which adjacent filtering means are in substantial contact with one another. In this configuration, some of the filtering means in the matrix may remove different components of the imaging signal compared to some other filtering means in the matrix. For example, the matrix of filtering means may be filtering means having at least substantially orthogonal or normal polarization orientations arranged in a grid pattern. The components set forth above can be discrete or integrated. In one configuration, the filters and/or retarder can be in the form of one or more coatings on a suitable substrate (such as an optically flat, transparent surface). In that event, the first and second encoding means typically contact one another. In one configuration, the second encoding means can have an edge coated with an electromagnetic radiation-absorptive material. The components and techniques can be employed in a wide variety of devices and applications to produce 3D images. In one implementation, the location of part of the filter set forth above is located at the aperture stop in a condenser. A half-wave retarder can be used in that position so that the condenser can operate as an unconverted condenser. In another implementation, the components are configured as an adapter between a camera and an unmodified microscope to produce stereoscopic images. In either implementation, the filter is preferably not located adjacent to or inside the objective to permit use of magnification powers higher than 10X, reduce cost and distortion, and enhance the interchangeability of lenses among imaging systems and the ability for multiple objectives to maintain a common focus. The foregoing summary is neither exhaustive nor limiting. As will appreciated, features and/or elements noted above can be combined in any number of ways not set forth above. Such combinations and extensions are considered to be a part of the invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows in cross-section the components that make up a Half- Wave Retarder Stereoscopic Light- Valve. FIG. 2 shows an exploded view of the components that make up a Half- Wave Retarder Stereoscopic Light- Valve. FIG.3 shows in cross-section the Half- Wave Retarder Stereoscopic Light- Valve as laminate on the polarization rotator. FIG. 4 shows in exploded view the components that make up a stereoscopic video lens. FIG. 5 shows diagrammatically a relay lens creating a conjugate of the original aperture stop. FIGS. 6A and 6B show alternative positions for the leading polarizer. FIGS. 7A, 7B, 7C, and 7D show alternative positions for the polarization rotator. FIG. 8 shows an alternative position inside the camera body for the polarization rotator. FIGS. 9A and 9B show alternative positions for the analyzing polarizing filter. FIGS. 10A and 10B show the effects of opposing linear polarizing filters on the aperture stop. FIG. 11 shows the effect of the Half- Wave Retarder Stereoscopic Light- Valve. FIGS 12 A, 12B, and 12C show the three states (two powered and one unpowered) of an FLC polarization rotator. FIGS 13A, 13B, and 13C show the effect of the three states of an FLC polarization rotator on the light path. FIGS. 14A, 14B, 14C, and 14D show four treatments for the cut edge of a half-wave retarder. FIG. 15 shows in abstract the circuitry used to control the polarization rotator. FIGS. 16A, 16B, and 16C show three of many possible variation on the cut of the half wave retarder. FIG.17 shows a microscope constructed using the Half- Wave Retarder Stereoscopic Light-Valve. FIG. 18 shows a still camera attachment for a microscope constructed using parts from the Half- Wave Retarder Stereoscopic Light- Valve. FIG. 19 shows a video camera attachment for a microscope constructed using the Half- Wave Retarder Stereoscopic Light- Valve with the polarization rotator below the half- wave retarder. FIG. 20 shows a video camera attachment for a microscope constructed using the Half- Wave Retarder Stereoscopic Light- Valve with the polarization rotator above the half- wave retarder. FIG. 21 shows in exploded view the components that comprise the Two-Polarizer Stereoscopic Light- Valve. FIG. 22 shows in abstract that opposing polarizing filters do not need to be orthogonally opposed. FIG. 23 shows a simple microscope constructed using circular polarization. FIG.24 shows the components in abstract that comprise a Micro-Filter Stereoscopic Light-Valve. FIGS. 25A, 25B and 25C show variations on the filters placed over the pixels that are a part of the Micro-Filter Stereoscopic Light- Valve. FIG. 26 shows in abstract a video adapter for an endoscope constructed using a Micro-Filter Stereoscopic Light- Valve. FIG. 27 shows the effects on the aperture stop as it would appear at each ocular if each ocular could image the aperture stop. FIG. 28 shows that the effect on the aperture stop is the same when neutral density filters cover half the created aperture stop in a relay lens system inserted ahead of each ocular, thus defining a Fixed Occluder Stereoscopic Light- Valve. FIG. 29 shows in abstract that one side of the aperture stop must effect the passage of an image signal differently from the other half. FIG. 30 shows that the effects on the aperture stop need not be simultaneous at the same aperture stop. FIG. 31 shows a significant improvement over the Carter 1988 patent. FIG. 32 shows the Carter 1988 PRIOR ART microscope objective. FIG. 33 shows in cross-section a stereoscopic ocular. FIG. 34 shows in cross-section a stereoscopic ocular adapter. FIG. 35 shows variations on the construction of a neutral density filter. FIG. 36 shows variations in the density of a neutral density filter. FIGS.37A and 37B show variations on the edge treatment of a neutral density filter. FIG. 38 shows in cross-section the components that comprise a 3D video adapter constructed using the Half- Wave Retarder Stereoscopic Light- Valve. FIG.39 shows in exploded isometric view the components that comprise a 3D video adapter constructed using the Half- Wave Retarder Stereoscopic Light- Valve. DET AILED DESCRIPTION OF THE PREFERRED EMBODIMENT A. Stereoscopic Light Valves Dividing the aperture stop of a lens system in a manner that allows one eye of the viewer to perceive the light passing through one part of the aperture stop, and that allows the other eye to perceive the light passing through the other part of the aperture stop, results in the viewer perceiving a 3D image of the subject being imaged by the lens system. In the absence of a viewer or absence of viewing hardware, the image transformed by the division of the aperture stop can be called encoded. That image signal contains in its out-of-focus area the information needed to later construct a 3D image. A device, which when interposed at the aperture stop of a lens system, and which causes a difference of transmission through its parts so as to encode depth information into the out-of-focus parts of the image signal is an apparatus referred to herein as an image signal encoding filter or a stereoscopic light-valve. As noted above, any statement that an optical component is to be located at the aperture stop is intended also to encompass locations near the aperture stop. 1. Half- Wave Retarder Stereoscopic Light- Valve Shown diagrammatically in FIG. 1 is a half-wave retarder stereoscopic light-valve capable of insertion into the aperture stop of any imaging lens system to enable that lens system to produce stereoscopic video, still, or motion picture image sequences, also called "frame sequential" images. This half-wave retarder stereoscopic light-valve can be retrofitted into any existing lens system and can be manufactured into any new lens system. Examples of such a lens systems include microscopes, endoscopes, video lenses, still camera lenses, ocular fundus lenses, inspection lenses, video lens adapters, still camera lens adapters, binocular adapters, monocular adapters, and motion picture lenses. Although these examples are the only ones cited, they are not intended to be limiting. Any imaging lens system can be used to exploit this half-wave retarder stereoscopic light-valve and such unforeseen applications are considered a part of this embodiment. This half- wave retarder stereoscopic light- valve is one embodiment of an image signal encoding filter. The half- wave retarder stereoscopic light-valve is capable of producing a sequence of images that can later be viewed in 3D, also called stereovision or human stereopsis. FIG. 1 illustrates diagrammatically such a half-wave retarder stereoscopic light-valve. The half-wave retarder stereoscopic light-valve is a sandwich made of four components. A leading polarizing filter 1 is first in the light path. A final polarizing filter 2 is last in the light path. Between the two is a half-wave retarder 3 and a polarization rotator 4. The polarizing filters 1 and 2 are preferably first and last in the light path. The half-wave retarder 3 and the polarization rotator 4 can appear in the order shown or in the reverse order with no difference in function. The half-wave retarder stereoscopic light- valve is constructed as thin as necessary to avoid space conflict with any lens elements that surround the aperture stop. Although the diameters or sizes of the various components depend on the diameter of the signal at the location of the particular component, the thickness of the light valve typically ranges from about 1mm to about 15mm and the diameter of the light valve from about 1mm to about 10cm. In the event that materials prevent a sufficiently thin construction such that the entire half-wave retarder stereoscopic light-valve occupies only the space of the aperture stop, the half-wave retarder stereoscopic light-valve is placed such that the half-wave retarder component, is at or near the aperture stop. FIG. 2 is an exploded view of the stereoscopic light- valve. It shows that the half- wave retarder 3 covers approximately one-half the area of the aperture stop with the edge 5 oriented vertically or near vertically. The vertical orientation is relative to normal upright orientation of the lens into which the adapter is installed, or when the lens is not horizontal the vertical orientation is relative to the normal upright orientation of the intended imaged object. Preferably, the polarization rotator 4 should be positioned such that it can rotate the inbound polarization orientation of light by approximately 90 degrees from the orientation that it passes when it is in an alternately powered state. The power to rotate, or not to rotate, is supplied by cables or wires 6. The final polarizing filter 2 preferably has its polarization orientation oriented approximately in parallel with the polarization orientation of the leading polarizing filter 1, or approximately orthogonally opposite to it, or approximately 45 degrees to it, as required by the particular nature of the polarization rotator selected. FIG.3 shows that the half- wave retarder stereoscopic light- valve can be constructed from coatings or laminations on the polarization rotator 4. A half-wave retarder 3 is first coated or laminated to one half of one of the polarization rotator's faces. Two appropriately aligned polarizing filters are then coated or laminated to both sides of the faces of the polarization rotator, the leading polarizing filter 1 to one face, and the trailing polarizing filter 2 to the other face. Shown in FIG. 4 is an apparatus that is illustrative of the Half- Wave Retarder Stereoscopic Light- Valve. FIG.4 shows a typical lens system capable of imaging a subject 7, image signal encoding the subject's depth information with a leading polarizing filter 1, a half-wave retarder 3 at the aperture stop of the lens, a polarization rotator 4, and an analyzing polarizing filter 2, and recording that image on the image plane 8. The image plane 8 of a typical camera, the body of which is represented by dashed line 9, is the front surface of an Image Orthicon tube, a CCD array, CMOS array, positive film, negative film, or any other image recording surface or surfaces. The camera is analog or digital. The lens system is capable of producing a sequence of images that can later be viewed in 3D, also called frame sequential stereovision or human stereopsis. FIG. 4 illustrates such a lens system. Any of many common forms of lenses are represented by the cylinder pictured at 10. Although FIG. 4 shows a fixed focal length lens, this assumption is not intended to be limiting, however, because it is well known that lenses can be constructed to vary their focal length, such lenses commonly being referred to as "zoom" lenses. Such variable focal length lenses may nevertheless be employed in the invention and those skilled in the optic arts will readily be able to extend the present principles to variable focal length lenses. A half- wave retarder 3 is placed at the aperture stop of the lens system 10. This assumption is not intended to be limiting, however, as it is well known that lens systems may have multiple effective aperture stops, called the aperture stop and its conjugates. Such alternate locations of the aperture stop may nevertheless be employed in the invention and those skilled in the optic arts will readily be able to extend the present principle to any conjugate of the aperture stop. The assumption that the aperture stop is interior to the lens system is also not intended to be limiting, however, because it is well known that new conjugates of the aperture stop can be constructed in the light path prior to and/or in the light path subsequent to the an existing lens system. FIG. 5 shows one example of a new conjugate of an aperture stop created in the light path subsequent to an existing lens system 10. A typical relay lens system, shown bracketed by 11, gathers the image at the original image plane represented by the dashed line 8, and focuses a new image on a new image plane represented by the dashed line 12. Between the old and new image planes a new aperture stop—the position of which is indicated by the dashed line 58 (a conjugate of the original aperture stop) is created and the half- wave retarder 3 placed at that point. Such new conjugates of aperture stops, whether in the light path prior to or in the light path subsequent to the lens system, may nevertheless be employed in the invention and those skilled in the optic arts will be readily able to extend the present principle to placement of the half- wave retarder in any such created external conjugate of the aperture stop. FIG.4 shows that the half- wave retarder 3 preferably covers approximately one-half the area of the aperture stop with the bisecting edge 5 oriented vertically or near vertically. The vertical orientation is relative to normal upright orientation of the camera body, represented by the dashed line 9, to which the lens system 10 is attached. This orientation is not intended to be limiting, however, as it is well known that some lens systems rotate during use. For lens systems that rotate, the half-wave retarder 3 either attaches to a non-rotating component at the aperture stop, or is installed with hardware able to maintain the vertical orientation of its edge while the lens system rotates, or is placed in a new external aperture stop that does not rotate with the lens system. Such positioning or hardware modifications may nevertheless be employed in the invention and those skilled in the optic arts will readily be able to extend the present principles to any position or modification required to maintain a vertical orientation of the bisecting edge of the half- wave retarder in a rotating lens system. The preferred polarization orientation of the half- wave retarder 3 approximately parallels that of the polarization orientation of the leading polarizing filter 1. When the leading polarizing filter 1 is external to the lens system, it adjusts to bring its polarization orientation into alignment with the half- wave retarder ' s polarization orientation. When both are external, one or the other or both adjust. When both are internal to the lens system, both are fixed in the correct orientation relative to each other during manufacture. This is not to be taken as limiting, however, because the orientations can be at any angle to each other, and the optimum angle is defined by the nature of the polarization rotator. If the polarization rotator is an LC device, the orientations are generally either parallel or orthogonally opposed, whereas if the polarization rotator is an FLC device, the orientations are generally at 45 degrees, or at 135 degrees. As shown in FIG. 4, a leading polarizing filter 1 is interposed anywhere in the light path between the light source, which may be reflected light off the subject 7, or may be light transmitted through the subject 7, and the half-wave retarder 3. The preferred position for a lens that is not dedicated to a single use is external to the lens system and optionally attached to the front of the lens system, as for example with a screw-on filter. Other positions are anywhere inside the lens system, FIG. 6A at 1, or as a coating on the front element of the lens system as shown in FIG. 6B at 13, that is, anywhere in the light path prior to the half- wave retarder 3 in both figures. The external position 1 of FIG. 4 is preferred for lenses that are not dedicated to a single use because it requires minimal modification of the lens. That position is not intended to be limiting, however, as it is well known that polarizing filters can be applied as coatings to lenses and can be positioned almost anywhere inside a lens system. Any position for the leading polarizing filter may be employed in the invention so long as it is anywhere in the light path between the subject and the half-wave retarder, and those skilled in the optic arts will readily be able to extend this principle to any acceptable position inside or outside of the lens system. The polarization orientation of the leading polarizing filter 1 in FIG. 4 must be approximately parallel to the polarization orientation of the polarization rotator 4 when the polarization rotator is powered or unpowered and is in one or the other of its two positions. This is not to be taken as limiting, however, because this orientation will depend on the nature of the polarization rotator. For example in one configuration, an LC polarization rotator requires the orientations to be either parallel or approximately 90 degrees opposed. Whereas for a FLC polarization rotator, for example, the orientation in one configuration is better at 45 degrees to the unpowered state, or 135 degrees to the unpowered state. When the leading polarizing filter 1 is in the light path prior to the lens system it is manually adjustable for alignment. When the polarizing filter is internal to the lens system as with 1 in FIG. 6A, or is applied to a lens as 13 in FIG. 6B, adjustment is made by altering the position of the polarization rotator. When the polarization rotator is also inside the lens system 4 in FIG.7A, adjustment is manufactured into all components of the lens system. The means of orientation is not intended to be limiting, however, as it is well known that a polarizing filter can be oriented using any of a number of well known means. Any such means may nevertheless be employed in the invention and those skilled in the optic arts will readily be able to extend this principle to any means of orientation. As shown in FIG. 4, a polarization rotator 4 is placed anywhere in the light path between the leading polarizing filter 1 and the analyzing polarizing filter 2. Position 4 is the preferred implementation because it requires a component of minimal expense (smaller size). FIGS. 7A, 7B, 7C, and 7D show other acceptable positions. The polarization rotator may be positioned anywhere in the optical path between the leading polarizing filter 1, and the analyzing polarizing filter 2. The position of the polarization rotator is irrespective of the position of the half- wave retarder 3. The polarization rotator can be placed inside the lens and in the light path subsequent to the half-wave retarder 3, as in FIG. 7A at 4, or inside the lens and in the light path prior to the half-wave retarder 3, as in FIG. 7B at 4, or in the light path prior to the lens and in the light path subsequent to the leading polarizing filter 1, as in FIG. 7C at 4, or in the light path subsequent to the lens and in the light path prior to the analyzing polarizing filter 2, as in FIG. 7D at 4. In FIG. 4, the orientation of the polarization rotator 4 is set appropriately for the leading polarizing filter 1, as described above. When the polarization rotator is installed in an external housing prior to the lens system as at 4 of FIG. 7C it may or may not be made adjustable. When the polarization rotator is installed inside the lens system, as at 4 of FIG. 7B or FIG. 7 A, the leading polarizing filter is adjustable when external at 1. When both the polarization rotator is internal, and the polarizing filter is fixed, the lens systems may be manufactured in permanent correct alignment. When the polarization rotator is inside the camera body, it is adjustable when the camera body allows, otherwise it is non-adjustable. When the polarization rotator is non-adjustable, then either the leading polarizing filter is adjustable, or the lens system is manufactured to permanently align with the fixed polarization rotator. The polarization rotator requires two different voltage potentials to set it into one or the other of its polarizing effecting orientations. When the polarization rotator is internal, as at 4 of FIG. 7 A or FIG. 7B, energy is supplied either via a corresponding external cable 6 or via electrical contacts 14 in the lens system's housing. When the polarization rotator is external, FIG. 7C or FIG. 7D, energy is supplied via external wires 6. As shown in FIG. 8, when the polarization rotator 4 is inside the camera body 9, energy is provided via the internal camera body wires 6. In FIG. 4, the analyzing polarizing filter 2 is placed anywhere in the light path between the half- wave retarder 3 and the image plane 8. The preferred implementation is outside the lens system at 2 and in proximity to the polarization rotator 4, because this placement allows the lens system to be used for other purposes when not being dedicated to stereoscopic use. Other locations for the analyzing polarizing filter are shown in FIGS. 9A and 9B. The analyzing polarizing filter, when inside the lens system 10, must be in the light path subsequent to the half-wave retarder 3, as at 2 in FIG. 9A; when the analyzing polarizing filter is inside the camera body 9, it is preferably in the light path prior to the image plane 8, as at 2 in FIG. 9B. As in FIG.4, the analyzing polarizing filter 2 has its polarization orientation oriented appropriately for the polarization orientation of the leading polarizing filter 1 as described above, or approximately orthogonally opposite to it. When the analyzing polarizing filter is outside the lens system as at 2, it may be adjustable to achieve proper orientation. When the analyzing polarizing filter is inside the lens system, as in FIG.9A, or inside the camera body, as in FIG. 9B, the analyzing polarizing filter may be internally adjustable, or may be manufactured to be in the correct alignment. The reference of a polarization rotator in general is not to be taken as limiting. Any of a broad range of existing or later developed opti-electronic devices may be use to produce the desired effect. Among those existing at this time are FeroElectric Liquid Crystal (FLC or FELC) switches, Liquid Crystal (LC) switches, and Pi cells. Any of these or future opti- electronic devices may be used to produce the desired effect of polarization rotation, and the selected device shall still be a part of this invention. In one configuration, the polarization rotator is thus any of a class of devices that can change the orientation of polarized light by approximately 90 degrees between its two states. Use of an FLC or FELC switch is, however, not intended to be limiting, as it is well known that polarized light can be reoriented by 90 degrees in alternating directions by many means, both electric and mechanical. Any such implementation may nevertheless be employed in this configuration and those skilled in the optic arts will readily be able to extend this principle to any means for reorienting polarized light by approximately 90 degrees between its two states. The specification of 90 degree rotation is also not intended to be limiting because a polarization rotator can be variable in its rotation. Preferably, any degree of rotation that sums to a total polarization orientation change of approximately 90 degrees is acceptable, and any such alternate divisions of rotation are a part of this embodiment. As shown in FIG. 14A, the bisecting edge 5 of the half- wave retarder 3 may be treated to minimize unwanted refractive visual noise. One implementation is to coat the bisecting edge with light-absorptive material, such as flat-black paint, dye, or a light absorptive agent. Another implementation, as shown in FIG. 14B, is to apply the half- wave retarder as a coating 15 to an optically flat transparent surface 16, such as glass. Another implementation, as shown in FIG. 14C, is to sandwich the half- wave retarder 3 along with transparent filler material 17 between two optically flat transparent surfaces 16, such as glass. FIG. 14D shows that the leading polarizing filter 1 can be included in a sandwich with the components of FIG. 14C, where the leading polarizing filter precedes the passive half- wave retarder in the light path. These implementations are not intended to be limiting, however, as it is well known that edge refractions can be eliminated using any of a wide variety of means. Any such means may nevertheless be employed in the invention and those skilled in the optic arts will readily be able to extend this principle to any means for eliminating undesirable edge refraction. In FIG. 2, the orientation of the polarization rotator 4 parallels that of the leading polarizing filter 1. The two parallel each other when the polarization rotator is in one or the other of its electrically energized or non-energized orientations but preferably not both. The polarization orientation of the half- wave retarder 3 is appropriately orientated to that of the polarization orientation of the leading polarizing filter 1. Current producers of passive half- wave retarder material mark the grain or neutral orientation of the material with an arrow or other indicator at the edge of the material. The material preferably is rotated 45 degrees in either direction relative to its neutral orientation to bring its active polarization orientation into appropriate alignment with the leading polarizing filter. The polarization rotator 4 is electrically energized, or not, to set it into one or the other of its polarizing effecting orientations. The polarization rotator 4 is provided its energy via the wires 6. The energy supplied to, or made absent from, the polarization rotator toggles it from one orientation setting to the other and back again. As shown in FIG. 15, a signal originates at 18 inside the camera 9 and is passed to a converter box 19 over the wires 20. The converter box 19 converts the internal signal produced by the camera into a form usable by the polarization rotator 4. The converted signal is passed from the converter box 19 to the polarization rotator 4 via wires 6. The converter can convert a standard analog or digital video signal into a square wave for use by the polarization rotator. The conversion from analog or digital to a square wave is intended to be illustrative of the general principle and is not intended to be limiting. Any method to drive the polarization rotator may nevertheless be employed in the invention, and those skilled in the electric arts will readily be able to extend the present principles to an appropriate conversion circuit. That orthogonally opposing polarizing filters are referred to is also not to be taken as limiting. As shown in FIG. 22, an image signal encoding filter 21 can be constructed of two elements 22 and 23 that cause light to be polarized in different directions. For the purposes of this example, consider that the two filters shown are oriented 60 degrees off from the vertical in opposite directions. Their orientation to each other, in this example, would be 120 degrees, not 90 degrees (not orthogonally opposite). Yet this orientation can still be made to work well. The image signal, as indicated by dashed line 24, passes through the image signal encoding filter 21 and is subsequently split into two image signals 25 and 26 by beam splitter 27. The rightmost image arrives at analyzing filter 2 which is oriented perpendicular to the orientation at 23, thus causing that half of the aperture stop to be perceived as opaque. The leftmost image arrives at analyzing filter 28 which is oriented perpendicular to the orientation at 22, thus causing that half of the aperture stop to be perceived as opaque. The perceived 3D effect for the non-orthogonally opposing image signal encoding filter halves 22 and 23 is the same as the perceived 3D effect or orthogonally opposing image signal encoding filter halves, as at 29 and 30 of FIG. 10A. Clearly, there is no need for the polarizing orientations at the aperture stop of the system to be orthogonally opposing. That we stress orthogonally opposing is for simplicity of construction and to minimize light loss. The half-wave retarder stereoscopic light-valve only requires use of a passive element or manipulative means at the aperture stop of the lens system. This approach has several advantages over the other light valves. The typical stereoscopic "light-valve" is composed of two opposing linear polarizing filters as shown in FIG. 10 A. The vertical orientation indicator 29 shows that the left side of the aperture stop is covered with polarizing material that polarizes in the vertical orientation. The horizontal orientation indicator 30 shows that the right side of the aperture stop is covered with polarizing material that polarizes in the horizontal orientation. FIG. 10B shows a sequence of effects on the aperture stop caused by a polarization rotator. Each half is opaqued alternately, one occluding and the other allowing light through, then the second occluding and the first allowing light through the first half. The light passing parts are typically oriented in opposing polarizing orientations. When opposing sides of the aperture stop are orthogonally polarized, an interesting effect is imposed on the viewer of the resulting images. Sky, water, and other reflecting and polarizing effecting surfaces will appear different to each eye. Sky, for example, will appear very dark to one eye and will appear very light to the other eye. This can appear to strobe in video and film presentations, and lead to eyestrain when used with still image presentations. The half-wave retarder stereoscopic light-valve is quite different and produces a much more pleasing effect. As shown in FIG. 11, non-polarized light enters the light path at 31. A leading polarizing filter 1 polarizes all or substantially all of the light entering the system in a single orientation as shown by indicator 29. Whatever polarizing orientation outside subjects may have had, such as sky, will be polarized once and uniformly. If the sky is dark, for example, it will remain dark thereafter. A half-wave retarder 3 is placed at the aperture stop and cut so that it only occupies one half of the aperture stop. A correctly oriented half- wave retarder will shift the polarizing orientation of the light passing through it preferably by 90 degrees. The result on the light path is a left side orientation that is oriented one way as at 29, and a right side that is oriented the orthogonal way as at 30. But note that the polarizing effect on the sky was done once by the leading polarizing filter 1, and remains the effect thereafter. The change in one half the aperture by the passive half- wave retarder only effect the polarizing orientation of the light, not the image that is being passed through it. The half-wave retarder stereoscopic light-valve can be used with sky, water, and other reflecting and polarizing altering materials with no conflict between what each eye sees. It does not strobe when used with video and movies, and produces no eyestrain. Another advantage of the half- wave retarder stereoscopic light- valve is that it places a passive component at the aperture stop of the lens system. The passive half- wave retarder 3, once installed, requires no maintenance and no adjustment over time. Because it is passive, unlike active "light-valves," it is neither prone to failure nor prone to need for periodic replacement. In addition to the passive element that is at the aperture stop, a polarization rotator is used in one configuration which can be anywhere in the light path between the leading and analyzing polarizing filters, but which is generally not placed at the aperture stop. FIG. 12A shows a polarization rotator 4 that is powered by wires 6. When that polarization rotator is an FLC, its non-powered state has the effect on polarizing orientation that is neutral. This allows light to pass through both sides of the aperture. This system fails in a way that allows a fully lit image to pass, but only loses 3D information. Such a failure mode is critical in such fields as medicine and other life-critical missions. FIG. 12B shows the effect when a polarization rotator that is an FLC is powered one way 32. It rotates the polarization orientation of light to one polarizing orientation. When it is powered in the other direction, as at 33 in FIG. 12C, it rotates the polarization orientation of light to the other polarizing orientation. FIGS. 13A, 13B, and 13C show the effect of the three polarizing orientating directions of a polarization rotator that is an FLC when combined with a trailing polarizing filter 2 (also called an analyzing polarizer). FIG. 13 A shows that when the polarization rotator that is an FLC is in its neutral orientation 4 the polarization orientation of the two halves of the aperture stop are typically rotated 45 degrees, thus allowing both sides to pass through the trailing polarizing filter 2. FIG. 13B shows that when the polarization rotator that is an FLC is powered into its counter clockwise direction 32, the polarization orientation of the two halves of the aperture stop are typically rotated 90 degrees thus allowing only the light from the passive half-wave retarder 3 side of the aperture stop to pass through the trailing polarizing filter. FIG. 13C shows that when the polarization rotator that is an FLC is powered into its clockwise direction 33, the polarization orientation of the two halves of the aperture stop are left in their original orientation, thus allowing only the light from the unoccupied side of the aperture stop to pass through the trailing polarizing filter. Because only the half-wave retarder 3 needs to be in the aperture stop, the other components can be installed outside the lens system. Such an arrangement leaves a lens system that acts as though it is unmodified unless combined with the other components. This arrangement has the advantage of allowing the creation of lenses that can be used for work other than 3D image production, a concern that many users will have when faced with a choice between single-use and multiple-use with very expensive lenses. That there is no description of the configuration having the fewest reflecting surfaces is not intended to be limiting. It is well known that quality optical components are often coated with anti-reflective materials. Typically, any such anti-reflective coating may be used to reduce the reflective properties of the signal encoding filter, and any such anti- reflective coatings may be used with, will become a part of this invention. That the half- wave retarder is said to occupy approximately one half of the aperture stop is not intended to be limiting. A straight bisection is not necessary for the 3D effect to work. FIGS. 16 A, 16B, and 16C each show a half- wave retarder 3 which occupies approximately one half of the aperture stop, but which does not linearly bisect the aperture stop. Typically almost any shape will work provided there is an approximately equal division of area between the two sides of the aperture stop and those skilled in the optic arts will be readily able to extend this principle to most any shape while not deviating from the intention of this invention. That the half-wave retarder is said to occupy one side of the aperture stop is not intended to be limiting. The half-wave retarder may occupy either side of the aperture stop, and the choice of side will only effect the orientation and placement of the related leading and analyzing polarizing filters and the polarization rotator. That there is no specification of an achromatic half- wave retarder is not intended to be limiting. Achromatic half- wave retarders are necessary in applications where the true rendering of visual colors is desirable, but are not necessary where such renderings are not necessary, as in black and white imaging. Clearly those skilled in the optic arts will be readily able to select the most desirable quality of half-wave retarder based on specific application requirements, and any such selection shall be considered a part of this invention. That half- wave retarder is specified is not intended to be limiting. It is well known that half-wave retarding effects can be achieved by sandwiching two quarter- wave retarders, nevertheless any construction of half- wave retarding effect shall be a part of this invention. That a half-wave retarder is preferably located at the aperture stop is not intended to be limiting. When the half-wave retarder, or other image signal encoding filter piece, acts as an occlusion that blocks half the aperture stop, it reduces the total light passed through the lens system by 50%, or one stop and in no other way affects the image. If that occlusion is moved from the aperture stop, however, the effect is much different. If, for example, it is located at a distance that is equal to the lens diameter away from the aperture stop, on an f/2 lens, the effective lens speed reduces dramatically. For light entering the lens 27 degrees off- axis, the effective speed of the lens reduces to f/5. For light entering the lens 45 degrees off- axis the effective speed of the lens reduces to f/10000, effectively zero transmission of light. The visual effect of an image produced by such a lens is one of a vignetted picture, or of tunnel vision. The further the filter is from the aperture stop, the more pronounced this aberration becomes. Actual experience shows visually perceptible vignetting when, on an f/2, 50mm lens, the occlusion is only 2mm from the aperture stop. In general then, the image encoding filter must be either at the aperture stop or near the aperture stop, and in no instance should it be future from the aperture stop (on either side of the aperture stop) than the diameter of the aperture stop. 2. Half- Wave Retarder Binocular Light- Valve That a polarization rotator and an analyzing polarizing filter are specified is not intended to be limiting. FIG. 17 shows diagrammatically that the half- wave retarder 3 can be equally well followed by a beam-splitter 27 and separate analyzing polarizing filters 2 and 28 intended for binocular viewing. A half-wave retarder binocular light-valve is a system capable of insertion into the light path of any binocular or monocular imaging lens system to enable that lens system to produce stereoscopic images for direct viewing. This half- wave retarder binocular light-valve can be retrofitted into any existing binocular or monocular imaging system and can be manufactured into any new binocular or monocular imaging system. Examples of such a systems include microscopes, telescopes, and inspection devices. Although these examples are the only ones cited, they are not intended to be limiting. Any imaging lens system can be used to exploit this half- wave retarder binocular light-valve and such unforeseen applications are considered a part of this embodiment. This half- wave retarder binocular light-valve is one embodiment of an image signal encoding filter. FIG. 17 shows a claimed apparatus that is illustrative of this Half- Wave Retarder Binocular Light- Valve. FIG. 17 shows schematically the components that comprise a single lens microscope equipped for binocular viewing. A light source 34 provides illumination which projects upward to a condenser 35. The condenser 35 gathers the illumination and focuses it on a subject mounted on a stage 36. An objective 37 gathers the image of the subject and the focused light from the condenser and projects the image upward where it focuses as an aerial image suitable for viewing by oculars 38 and 39. When properly adjusted, the aperture stop in the condenser is a conjugate of the aperture stop in the objective lens, and the reverse relationship holds. The projected image from the objective lens 37 travels upward along the chief ray of the optical system as indicated by dashed line 40. A beam-splitter 27 splits the image, causing one half of the light carrying that image to be redirected toward the left hand ocular 38, and the other half to be redirected toward the right hand ocular 39. Human eyes 41 and 42 then perceive the magnified image of the subject. Despite two oculars, the magnified image in an unmodified microscope is in two dimensions. That a simple depiction of a light source 34 is depicted is not intended to be limiting. It is well known that light sources can be gathered and directed in a wide variety of manners. Clearly those skilled in the optical arts will be readily able to fabricate a light source well matched to the particular microscope so being equipped, and any such illumination or optical components used to achieve such illumination shall be usable with this invention. That a simple depiction of a condenser 35 is shown is not intended to be limiting. Condensers can be constructed to many degrees of quality and usefulness. Clearly those skilled in the optical arts will be readily able to fabricate a condenser well matched to the particular microscope so being equipped, and any such condenser shall be usable with this invention. That a simple depiction of a microscope objective lens 37 is illustrated is not intended to be limiting. Microscope objective lens can be manufactured to many degrees of quality and working distances, and any such objective lens shall be usable with this invention. That a prismatic depiction of a beam-splitter 27 is illustrated is not intended to be limiting because images for binocular viewing can be split from one image stream using any of many common mechanisms including half-silvered mirrors, prisms, and barrel prisms. No matter the mechanism employed, this invention shall be usable with any of them. That simple oculars 38 and 39 are specified is not intended to be limiting. Oculars can be manufactured in a range of magnifying powers and quality and any such oculars shall be usable with this invention. FIG. 17 also shows the placement of half- wave retarder binocular light- valve partly comprised of a half-wave retarder 3 at the aperture stop of the condenser which is the preferred location, or at any conjugate of the aperture stop. A half- wave retarder causes the orientation of polarized light passing through it to retard 90 degrees, thus changing the orientation of linear polarization by approximately 90 degrees, and changing the orientation of circular polarization from one handed to the other handed direction. The half-wave retarder is cut so that it occupies approximately one half the aperture stop. The cut is approximately perpendicular to the normal plane defined by the two oculars 38 and 39. The placement of a half- wave retarder is significantly easier and less expensive than the construction of a mechanically complex condenser. With no other changes to the optical path, the presence of the half- wave retarder in the condenser will have no effect on the image produced. This can be of advantage when condensers are swapped among microscopes. FIG. 17 also shows the placement of an enabling filter comprised of a leading polarizing filter 1 positioned between the light source 34 and the half-wave retarder 3. The illumination provided by 34 is polarized by the polarizing filter 1. Half that polarized light subsequently passes over the half- wave retarder 3 and the other half of that polarized light subsequently passes through the clear aperture stop unoccupied by the half- wave retarder. This results in one half the light transmitted through the aperture stop of the condenser being polarized one orientation, and the other half of the light transmitted through the aperture stop of the condenser being polarized in a different orientation. That a simple enabling filter comprised of a leading polarizing filter 1 is discussed is not intended to be limiting. It is well known that polarizing filters can be manufactured in many shapes and sizes, and, as is preferred, can be mounted inside holders, and can be equipped with handles to aid in rotation. Clearly those skilled in the optic arts will be able to devise a leading polarizing filter and mounts for the same that will be most suitable for this invention, and any such shape, mounting, or augmentation shall be considered to be a part of, and usable by this invention. That simple polarization is specified is not intended to be limiting. It is well known that polarized light can be rotated in three dimensions. When it is rotated in two dimension it is called linear polarization. When it is advanced through space in three dimensions, it is called circular polarization. Although the preferred embodiment is the use of linear polarization, either form of polarization can be used in this invention. FIG. 17 also shows placement of the analyzing filters comprised of polarization filters 2 and 28 located between the beam-splitter 27 and the human eyes 41 and 42. The orientation of the polarizers 2 and 28 must be oriented approximately orthogonality different from each other. That the preferred placement of the polarization filters 2 and 28 is illustrated as being between the beam-splitter 27 and the oculars 38 and 39 is not intended to be limiting. Polarizing filters can be also be mounted on, or inside, the oculars, and may also be placed over the eyes 41 and 42 as with polarized eyewear. That a beam-splitter 27 is discussed as being in its preferred position prior to the analyzing filters comprised of polarization filters 2 and 28, is not intended to be limiting. It is well known that beam-splitter can be fabricated that themselves split based on polarization orientation. Any of this class of beam-splitting devices that split based on polarization orientation may also be used in, and may become a part of this invention. When the enabling filter comprised of a polarizing filter 1 is correctly oriented, a stereoscopic image is produced for viewing by the human eyes 41 and 42. When the enabling polarizing filter 1 is rotated to a different orientation, either no stereo effect is produced (a 2D image is seen), or an inverse stereo (depth reversed) image is perceived. That the condenser 35 is illustrated as being below the stage 36 is not intended to be limiting. Some microscopes are constructed upside down so that live specimens in liquid can be viewed. In such microscopes, the condenser is above the stage and the objective lens below, nevertheless such inverted configuration shall be considered a part of this invention. The use of a half- wave retarder 3 significantly reduces the cost of manufacture for such a condenser as in 35. Only one optical component is added to the standard design for a condenser, and no moving parts are required. The use of an enabling filter that is comprised of a leading polarizer 1, usually external to the condenser, allows off-the-shelf parts to be used, again a significant reduction in the cost of manufacture. FIG. 18 shows a variation on FIG. 17. In FIG. 18 a still camera 9 replaces the binocular head of the microscope. An analyzing filter comprised of a final polarizing filter 2 is located between the camera 9 and the objective lens 37. The initial orientation of the analyzing polarizing filter 2 must either match the orientation of the enabling filter comprised of a leading polarizer 1 or must be oriented orthogonally different. When the enabling filter comprised of a leading polarizing filter 1 is oriented correctly, as indicated by arrow 43, one half the aperture stop in the condenser will appear occluded resulting in a photograph with either a right or left eye view. When the enabling filter comprised of a leading polarizing filter 1 is rotated 90 degrees, as indicated by arrow 44, the other half of the aperture stop in the condenser will appear occluded resulting in a photograph with the other eye view. Such sequences of right/left or left/right eye- view photographs will produce stereo pairs for later viewing. That a simple box shaped camera 9 is illustrated is not intended to be limiting. Any camera may be mounted on the microscope, including but not limited to large, medium, and small formats; black and white, or color; and analog or digital cameras. That the camera 9 replaces the binocular head is not intended to be limiting. It is well known that heads can be constructed such that both binocular viewing with human eyes and photography can be supported in the same device. Such microscope heads are called trinocular microscope heads and anyone skilled in the optic arts will be readily able to employ camera-only or multi-viewing microscope heads as needed. FIG. 19 shows a variation on FIG. 18. In FIG. 19 a video camera 45 replaces the still camera or the binocular viewing. As with the still camera (FIG. 18) an analyzing filter comprised of a final polarizer 2 is located between the objective lens 37 and the camera 45. For video capture, the orientation of the analyzing polarizing filter 2 must either approximately match the orientation of the enabling filter comprised of a leading polarizer 1 or must be oriented approximately orthogonally different. FIG. 19 also show polarization rotator 4 interposed anywhere between the enabling filter comprised of a leading polarizer 1 and the analyzing filter comprised of a final polarizer 2. FIG. 19 shows the polarization rotator in the preferred position when the intention is to make that component a part of the microscope. FIG. 20 shows the preferred position when the intention is to make that component a part of the camera assembly. FIGS. 19 and 20 also show a cable 6 which connects the frame timing circuitry of the video camera 45 to the driving circuitry of the polarization rotator 4. As each frame of the video sequence is shot, the polarization rotator changes the orientation of the polarization from one orientation to an orientation approximately orthogonally different for the next frame, and then back again. A video stream of images is thus produced, where the first image contains view information for one eye, and the next image contains view information for the other eye. That a simple box shaped video camera is illustrated is not intended to be limiting. Any camera may be mounted on the microscope, including but not limited to CCD, CMOS and Image Orthicon; black and white, or color; and analog or digital cameras. That video produces frame sequences is also not intended to be limiting because it well known that motion picture cameras also produce frame sequences, and may nevertheless also be used in this invention. That the camera 45 replaces the binocular head is not intended to be limiting. It is well known that heads can be constructed such that both binocular viewing with human eyes and frame sequence capture can be supported in the same device. Such microscope heads are called trinocular microscope heads and anyone skilled in the optic arts will be readily able to employ camera-only or multi-viewing microscope heads as needed. 3. Two-Polarizer Stereoscopic Light- Valve That a leading polarizing filter is followed by a half- wave retarder is not intended to be limiting. The effect produced by that combination is identical to the primary effect caused by two adjoining polarizing filters placed at the aperture stop of a lens system. FIG. 21 shows the components that comprise a two-polarizer stereoscopic light- valve, capable of insertion into the aperture stop of any imaging lens system to enable that lens system to produce stereoscopic video, still, or motion picture image sequences, also called "frame sequential" images, and into any binocular or monocular instrument to produced stereoscopic imaging. This two-polarizer stereoscopic light- valve can be retrofitted into any existing lens system and can be manufactured into any new lens system. Examples of such a lens systems include microscopes, endoscopes, video lenses, still cameras, ocular fundus cameras, inspection instruments, video lens adapters, still camera lens adapters, binocular adapters, monocular adapters, and motion picture lenses. Although these examples are the only ones cited, they are not intended to be limiting. Any imaging lens can be used to exploit this two-polarizer stereoscopic light-valve and such unforeseen applications are considered a part of this embodiment. The two-polarizer stereoscopic light- valve is one embodiment of an image signal encoding filter. FIG. 21 shows that first in the light path is a pair of polarization filters abutted together such that the joint between them approximately bisects the shape of the aperture stop. The first side 22 preferably is oriented approximately orthogonally opposite to the orientation of the second side 23. The preferred orientation is approximately 45 degrees to the joint, but any angles will work provided the two halves are approximately orthogonally opposite. That two separate polarization filters are specified is not intended to be limiting, because the preferred implementation is to laminate the polarization media to a common glass substrate. That the substrate is depicted as separate from the polarization rotator 4 is also not intended to be limiting, as the preferred technique is to laminate the opposed polarizing filters 22 and 23 (which are preferably oriented relative to one another with orthogonal polarization orientations) to the polarization rotator 4, using the polarization rotator 4 as the substrate. Second in the light path, is a polarization rotator 4. FIG. 21 also shows an analyzing polarization filter 2 subsequent in the light path to the polarization rotator 4. When the polarization rotator 4 rotates one quarter wave advanced and one quarter wave retarded, as with an FLC, the orientation of the analyzing polarizer 2 approximately parallels or is perpendicular to the joint between 22 and 23. When the polarization rotator 4 rotates one- half wave in advance, then returns to zero rotation, as with an LC, the orientation of the analyzing polarizer 2 is approximately parallel the polarization orientation of either half 22 or half 23. The preferred embodiment for the two-polarizer stereoscopic light-valve shown in FIG. 21 is to laminate all three components together into one unit. Of the three components, only the joined polarizer pieces 22 and 23 must be at the aperture stop of the lens system. The other components, 4 and 2, need not be at the aperture stop of the lens system. FIG. 23 shows a variation on FIG. 18. FIG. 23 shows a claimed apparatus that is illustrative of this Two-Polarizer Stereoscopic Light- Valve. Fig. 23 shows the construction of a simple mass market microscope. The encoding filter comprised of a combination of a half- wave retarder (3 of FIG. 18) located at the aperture stop of the condenser and an enabling filter 1 in the light path prior to the condenser, is replaced by a pair of orthogonally opposed circular polarizing filters in FIG. 23 at 46 and 47. The placement of circular polarizing filters at the aperture stop in the condenser and the placement of corresponding circular polarizing filters 2 and 28 in the microscope head allows low cost plastic filters to be used while maintaining acceptable image quality. The use of circular polarization relaxes the requirement for precise alignment of components to achieve a stereoscopic effect. The microscope head can be rotated an additional seven degrees beyond that allowed by linear polarizing without losing the stereoscopic effect. The oculars can themselves rotate around a common center, as on some brands of microscopes, without losing the stereoscopic effect. The condenser can be installed casually, as by the amateur, without degradation of the stereoscopic image. Circular polarization is the preferred method for producing the stereoscopic effect in a microscope. As will be appreciated, the methods disclosed herein may be applied to microscopes of any number of designs. One disadvantage to the use of opposing polarizing filters 22 and 23 of FIG. 22 is that they will generate different polarized views of the subject. When such an effect is present, as when light is reflected off a reflecting surface, the result will be scintillation in the stereoscopic image. When scintillation is undesirable, the half-wave retarder stereoscopic light- valve is preferred. 4. Micro-Filter Stereoscopic Light- Valve That standard camera imaging surfaces and devices are shown is not to be taken as limiting. Special coverings over the individual pixels of a digital imaging system can also be used to decode the captured encoded stereoscopic information. A Micro-Filter Stereoscopic Light- Valve is capable of insertion into the aperture stop of any imaging system to enable that imaging system to produce stereoscopic video, still, or digital motion picture image sequences, also called "frame sequential" images, and can also produce parallel video streams that are not frame sequential. This Micro-Filter stereoscopic light-valve can be retrofitted into any existing imaging system and can be manufactured into any new imaging system. Examples of such a imaging systems include video microscopy, video endoscopy, video cameras, still cameras, ocular fundus cameras, endoscopic devices, and digital motion picture cameras. Although these examples are the only ones cited, they are not intended to be limiting. Any imaging system can be used to exploit this micro-filter stereoscopic light-valve and such unforeseen applications are considered a part of this embodiment. The micro-filter stereoscopic light-valve is one embodiment of an image signal encoding filter. As shown in FIG. 24, an image signal encoding filter 48 is interposed in the light path (as indicated by dashed line 49) prior to the image gathering device 8. The image signal encoding filter is preferably located at the aperture stop of a lens system, or at any of the conjugates of the aperture stop, and is composed of two parts 50 and 51 which roughly equally divide the aperture stop into two parts. The two parts can be created either by two opposing linear polarizing filters, or by two opposing circular polarizing filters, or by combining a leading polarizing filter with a following half- wave retarder that occupies roughly one half of the aperture stop (the preferred means), or by opposing colored filters (anaglyphic), or by LC shutters. The encoded image is projected to focus on the image plane 8. That image plane is constructed of an CCD, CMOS, or other such digital image gathering apparatus. An image gathering apparatus with only two pixels of resolution is shown at 8. We limit this initial discussion to two pixels for simplification of description. Covering each pixel is a small filter, one for each pixel, that match or mirror the two filters in 48. That is for example, if 50 is vertical polarization, then 52 is a polarizing filter of the same or opposite orientation. When the two image signal encoding filters 50 and 51 are opposites of each other, and when the filters 52 and 53 are also opposites of each other, then one pixel will image the information from the first half of the aperture stop, and the other pixel will image the information from the second half of the aperture stop. It is well known that image gathering devices employ far more pixels than two. FIG. 25 A shows the preferred way to cover the pixels of such a device. The filters are arranged uniformly over the surface. In such an arrangement, the image will only need to be minimally magnified to twice its area so that both the A and B filters will perceive roughly equal images at the plane of focus with roughly equal resolution. FIG. 25B shows another arrangement that has benefit when the image can only be enlarged in the vertical direction. FIG. 25C shows yet another arrangement that has benefit when the image can only be enlarged in the horizontal direction. That only three arrangements of pixel filters are shown is not to be taken as limiting. Clearly algorithms can be developed that will prove one arrangement superior to another for a given application. Nevertheless any such arrangement shall be employed in this invention and those skilled in the optic or mathematical arts will be readily able to employ pixel filter arrangements of any desired pattern. That only rectangular arrays of pixels are shown is not to be taken as limiting because image gathering devices have been devised in may other geometric shapes. Octagonal pixel arrangements are also common. Clearly any such shape or geometric array of pixels may be employed in this invention, and those skilled in the electro-optic arts will be able to employ image gathering devices in many unforeseen and potentially useful shapes or collections of shapes. That, in FIG. 24, we show the image signal encoding filter 48 as two abutted filters is also not to be taken as limiting. As shown in FIG. 2, a half-wave retarder 3 may be interposed in the light stream subsequent to the polarizing filter 1, and that pair of components can replace the filter 48 of FIG. 24 with similar result at the image gathering surface of 8. This Micro-Filter Stereoscopic Light-Valve's chief advantages is that it does not use any active components. Instead of polarization rotators, this light-valve employs only static polarizing filters or static colored filters. Although it can operate with shutters, such shutters are not its preferred mode of operation. FIG. 26 shows a claimed apparatus that is illustrative of this Micro-Filter Stereoscopic Light- Valve. FIG. 26 shows schematically the proximal end of an optical endoscopic instrument 54. The image light rays indicated by lines 55 are refocused by a relay lens system 11 to create a new aperture stop (a conjugate of the original). An image signal encoding filter 48 is placed at the new aperture stop. The image light rays are encoded with 3D information by that filter, and are then focused further by the relay lens 11 onto the digital imaging surface 8. The digital imaging surface is covered with appropriate micro filters so that the single surface records both stereoscopic views. That simple lenses is shown is not intended to be limiting because in actual practice such lenses are composed of compound parts that are achromatic with spherical aberration corrections to produce a sharp and clear image. This depiction as simple lenses is not intended to be limiting because it is well known that a more complex lens will produce a superior image. Any quality of lens may nevertheless be employed in this invention and those skilled in the optic arts will be readily able to employ lenses of any desired quality. That a relay lens 11 is shown projecting onto an imaging surface is not intended to be limiting. The suggestion that the endoscopic device 54 originally imaged onto a surface is not the case. Either type of endoscope will operate with this system. One form of relay lens will relay an imaging device to a new image plane. Another form of relay lens will take an image suitable for viewing by human eyes, and will relay that image to a new image plane for recording. That a single image capturing surface is shown is not intended to be limiting. It is well known that color cameras can be constructed with 3 image capturing surfaces, one for each primary color. Image capturing surfaces of any number can by used with this invention, and all such variations in numbers of image capturing surfaces shall still be a part of this invention. 5. Fixed Occluder Stereoscopic Light- Valve That polarizing filters, colored filters, and other means of effecting transmitted light are shown is not intended to be limiting. When each eye views a common image through a separate apparatus, an occlusion can be interposed at the aperture stop inside each apparatus such that a 3D effect can be produced and perceived. An occluding stereoscopic light- valve is capable of insertion into the aperture stop of any imaging system to enable that imaging system to produce stereoscopic images. This occluding stereoscopic light-valve can be retrofitted into any existing imaging system and can be manufactured into any new imaging system. Examples of such an imaging systems include microscopes, telescopes, inspection instruments, binocular adapters, and monocular adapters. Although these examples are the only ones cited, they are not intended to be limiting. Any imaging system can be used to exploit this occluding stereoscopic light- valve and such unforeseen applications are considered a part of this embodiment. The occluding stereoscopic light-valve is one embodiment of an image signal encoding filter. FIG. 27 shows how one form of a single objective microscope that is equipped to produce 3D operates. The passive half-wave retarder 3 at the aperture stop 56 of the lens system 10, when combined with the leading polarizing filter 1, causes the two halves of the aperture stop to orient the polarization of each half orthogonally to the other half. The polarizing beam splitter 27 passes light of one polarization orientation to the left ocular 38 and light of the opposite polarization orientation to the right ocular 39. The diagram 57 shows how light passed through the aperture stop would be perceived by ocular 38 if the ocular could image the aperture stop. The diagram 58 shows how light passed through the aperture stop would be perceived by ocular 39 if the ocular could image the aperture stop. A viewed stereoscopic effect is caused by the perceived effect of the aperture stop's optical-encoding differing between the right and left oculars. The perceived effect of the aperture stop's optical-encoding is an important benefit of the invention. FIG. 28 shows a claimed apparatus that is illustrative of this Fixed Occluder Stereoscopic Light- Valve. FIG. 28 shows a non-3D binocular microscope that is modified to show 3D. An unmodified objective 37 and an unmodified beam splitter 27 cause identical images to be perceived by the two oculars 38 and 39. A relay lens system 11 is interposed in the light path prior to each ocular. Recall that a relay lens system 11 can create a conjugate 59 of the original aperture stop 56. By placing a image signal encoding filter 48 in each relay lens system 11, and by arranging for those image signal encoding filters to be orthogonally opposed, identical perceived effects, 57 and 58, of the aperture stop's conjugate 59 are produced as were the effects of FIG. 26 described above. 6. Mixing and Matching Light- Valve Parts That image signal encoding filters are disclosed with parts that are of similar materials is not to be taken as limiting. FIG. 10A, for example, shows an image signal encoding filter composed of two linear polarizing filters. FIG. 11, for example, shows an image signal encoding filter composed of a leading polarizing filter and a following half- wave retarder. FIG. 1 , for example, shows an image signal encoding filter composed of a sandwich of two polarizing filters, a half-wave retarder, and a polarization rotator. FIGS.27 and 28, for example, show an image signal encoding filter that is constructed from a passive occlusion. FIG. 23, for example, shows an image signal encoding filter that is composed of two circular polarizing filters. FIG. 24, for example, shows an image signal encoding filter composed of two opposing filters at the aperture stop and similar filters covering the pixels of an imaging surface, where those filters are either polarized, colored filters, or shutters. Clearly, the production of a 3D effect requires only that the parts of the aperture stop be differentiable from each other. Nothing in this invention shall prevent the mixing of types of encoding materials. Consider the filter parts 50 and 51 of FIG. 29. A filter can be constructed from non-intuitive parts, where, for example, the X is a blue filter (colored filter) and the Y is a circular polarizer (polarizing filter). As shown in the following Table, the X part may be of any construction, and the Y part may be of any other construction. Table 1: The mixing of encoder parts That a few possible combinations are identified shall not be considered limiting. Clearly, as other means of differentiating are devised, some of them may work in combi- nation with those heretofore disclosed, and any such use of new combinations with the current materials or methods, shall be a part of this invention. That the image signal encoding filters is described as preferably being at the aperture stop, or at one of the conjugates of the aperture stop, shall not be limiting. FIG. 30 shows schematically a lens system with two aperture stops 56 and 59. The image signal indicated by dashed line 24 passes first over filter 48 at the primary aperture stop 56, then subsequently passes over filter 60 at the conjugate of the aperture stop 59. Clearly image signal encoding filters can be devised that can be installed at the aperture stop and any of its conjugates. Likewise an image signal encoding filter can be devised that can be installed at two or more of the conjugates of the aperture stop. Nevertheless, any such positioning of image encoding filter components at multiple aperture stops and at multiple conjugates of aperture stops shall be a part of this invention. B. Embodiments that Use Stereoscopic Light- Valves As mention in the descriptions of the various light- valves, each can be placed at the aperture stop of various apparatuses to give 3D results. Hereafter follows a description of such apparatuses. 1. A Stereoscopic Microscope The first embodiment that uses a stereoscopic light valve is an apparatus that is a microscope with a single objective lens that produces a stereoscopic image when viewed through two oculars. This embodiment is a significant improvement over the prior art, which disclosed separate polarizing filters for each ocular and required the polarizing filters to be adjacent to the objective lens rather than at the aperture stop. Practical experience showed that such a position only yielded acceptable stereopsis at powers of lOx and lower. By moving the filter to the aperture stop, or to any of the aperture stop's conjugates, all powers are made to produce good stereopsis. In this embodiment, as shown in FIG. 31 , the separate polarizing filters of the prior art are replaced by a single polarizing beam splitter 27 in the binocular head of the microscope. The separate polarizing filters of the prior art tended to be placed too near the image plane of each ocular, subjecting them to dirt and other contaminants which reduced the quality of the viewed image. Polarizing filters also tended to be placed on the oculars, thus preventing useful rotation of the oculars (as for focusing), and caused them to easily fall out of alignment. Use of a polarizing beam splitter significantly simplifies manufacture and eliminates the problems associated with the earlier systems. In this embodiment, the prior art location of the filters adjacent to the objective , as in FIG. 32 PRIOR ART, are replaced, in FIG. 31, with the components of the Half- Wave Retarder Binocular Light- Valve, specifically a passive half-wave retarder 3 at the aperture stop of the objective, and a single polarizing filter 1 anywhere in the light path prior to that passive half-wave retarder. The dashed line at 64 in FIG. 31 shows the vertical plane that divides the lens into two equal plane-symmetric halves. The passive half-wave retarder 3 covers approximately one-half the area of the aperture stop with the bisecting edge 5 oriented approximately perpendicular to plane 64 of the system. This orientation is not intended to be limiting, however, as it is well known that the ocular head can be rotated to accommodate different users, and the orientation of the passive half- wave retarder is rotated in such circumstances to align with the polarizing beam splitter, inside the rotated head. That the components of the Half- Wave Retarder Binocular Light- Valve are shown is not intended to be limiting. Clearly, any of the other light-valves can be used at the aperture stop of the objective, with corresponding decoding devices at or subsequent in the light path to the beam-splitter. Such light-valves may include a Half- Wave Retarder Stereoscopic Light- Valve, or colored filters, or shutters. 2. Stereoscopic Producing Oculars and Ocular Adapters The second apparatus that uses a stereoscopic light valve is an apparatus that is a microscope ocular or ocular adapter constructed such that when two such oculars or ocular adapters are used in an ordinary binocular microscope head, or any binocular instrument, and when the two oculars or ocular adapters are rotated approximately 180 degrees relative to each other, they produce a true stereoscopic image of the magnified image. Such oculars and ocular adapters work on all lensing-objective microscopes equipped to accept at least two oculars and on any similar binocular device. FIG. 33 shows diagrammatically one such implementation of a lens arrangement for such a stereoscopic imaging ocular 61. A relay-lens system bracketed by 11 captures the image plane represented by the dashed line 8 produced by the microscope objective lens projection represented by lines 65. The relay-lens system relays the original image plane represented by the dashed line 8 to a new image plane represented by the dashed line 12. The new image plane represented by the dashed line 12 is viewed as an aerial image represented by 65, that is created by ordinary ocular optics suggested by 66. Alignment is via a marker, one example of which is shown at 67 or by mechanically coupling pairs together (not shown). FIG.34 shows diagrammatically one implementation of a lens arrangement for such a stereoscopic imaging ocular adapter 61. A relay-lens system bracketed by 11 captures the image plane represented by the dashed line 8 produced by the microscope objective lens projection represented by lines 65. The relay-lens system relays the original image plane represented by the dashed line 8 to a new image plane represented by the dashed line 12. The adapter is equipped with a sleeve 68 that allows any standard microscope ocular to be inserted when the diameter is the same specification. The relay lens system shown bracketed by 11 is depicted with simple lenses for the purpose of illustration. In actual practice, such relay lens systems are composed of compound lenses that are achromatic with spherical aberration correction to produce a sharp and clear image. This depiction as simple lenses is not intended, however, to be limiting because it is well known that more complex lenses will produce a superior image. Any quality of lens may nevertheless be employed in this invention and those skilled in the optic arts will be readily be able to employ lenses of any desired quality. A neutral-density filter 69 is placed at the created conjugate of the aperture stop 59 of the relay-lens system 11. FIG. 35 shows the shape of the neutral-density filter 69 that is placed at the aperture stop in the ocular or ocular adapter. The neutral-density filter is shaped to effect the transmission of light through one half the aperture stop. That it effects half the aperture stop is not, however, intended to be limiting. Occluding half the aperture stop has the effect of reducing the light through that aperture stop by 50%. Any effect of more or less of a 50% occluding may nevertheless be employed in this invention and those skilled in the optic arts will be readily be able to extend this principle to change the shape of the edge or cut to reduce or increase the amount of light transmission through the aperture stop by any desirable percentage. Such modifications of the cut or edge include moving its position to create an occlusion of greater or less than one-half a circle and shall still be a part of this invention. FIG. 35 also shows that the neutral-density filter may equally well be constructed as a hole cut through a circular plate 70. Although we show a semicircular cut, any shape hole may nevertheless be used. FIG.35 also shows that such a plate is also constructed from a cut half-disk 69 coupled with a half washer 71. FIG. 36 shows that the preferred implementation of a neutral density filter is to occlude the aperture stop at 100%. When the neutral density filter occupies half the aperture stop, a 100% blockage reduces the light transmitted through the entire aperture stop by 50%. Some applications may require less light loss. When the neutral density filter occupies half the aperture stop, a 50% reduction of light through the neutral density filter reduces the light transmitted through the entire aperture stop by 25%. When the neutral density filter occupies half the aperture stop and reduces light by 0%, it reduces the light transmitted through the entire aperture stop by 0%. A 0% occlusion eliminates the stereoscopic effect and is not recommended. That three percentages of occlusion in FIG.36 are illustrated is not, however, intended to be limiting. Any percentage of occlusion may nevertheless be employed in this invention and those skilled in the optic arts will be readily be able to employ a neutral density filter of any percentage of occlusion, as well as neutral density filters that can vary their degree of occlusion. FIG. 37 A shows the edge or cut 5 of the neutral-density filter 69. That edge or cut may be treated to minimize unwanted refractive visual noise. One implementation is to coat the edge or cut with light-absorptive material, such as flat-black paint, dye, or other light absorptive agents. Another implementation, as shown in FIG. 37B, is to apply the neutral- density filter as a coating 72 to an optically flat transparent surface 16, such as glass. These implementations are not intended to be limiting, however, as it is well known that edge refractions can be eliminated using a wide variety of methods. Any such method may nevertheless be employed in the invention and those skilled in the optic arts will readily be able to extend this principle to any method for eliminating undesirable edge refraction. That the neutral density filter is shown as occupying approximately one half of the aperture stop is not intended to be limiting. It is well known that other shapes can also produce acceptable 3D results, and any such variation in shapes can be used and will still be a part of this invention. Such variations need not be symmetric, nor need they be the same in each ocular or ocular adapter. That a neutral density filter is discussed is not intended to be limiting. Clearly, any material may be used such that one of its properties is to reduce the intensity of light passing through it. There could, for example, be benefit in using a mirror to reflect light back down the light path when this invention is used in top-lit microscopes. Or, for example, there could be benefit in using a plane polarizer when viewing polarized minerals. Any such material may nevertheless be employed in the invention and those skilled in the optic arts will readily be able to extend this principle to any material that includes among its properties that it will reduce the intensity of transmitted light. That the Fixed Occluder Stereoscopic Light- Valve is discussed is not intended to be limiting. Clearly, any of the other light- valves can be used at the aperture stop of the ocular or ocular adapter. Such light-valves may include colored filters, or polarizing filters, or retarders, or shutters, or mirrors. 3. A Generic Stereoscopic Lens Adapter The third apparatus that uses a stereoscopic light valve is an apparatus that, as shown diagrammatically in FIG. 38, is a stereoscopic lens adapter capable of enabling a wide variety of lenses and cameras to produce stereoscopic images. This adapter works with any lens that can be mounted at mount point 73. This adapter works with any camera that will accept the adapter's mounting hardware 74. The adapter captures the lens output image as represented by lines 65, and relays that image from the original image plane represented by the dashed line 8 to the video camera's new image plane represented by the dashed line 12. The image plane represented by the dashed line 12 of the camera 9 is the front surface of an Image Orthicon tube, a CCD array, CMOS array, or any other image recording surface, including positive and negative film. The camera is digital or analog. The stereoscopic lens adapter is capable of producing a sequence of images that can later be viewed in 3D, also called stereovision or human stereopsis. FIG. 38 illustrates diagrammatically such an adapter. The adapter is designed to allow a lens to be mounted at the adapter's front end 73, and to allow the adapter to be mounted to a camera body, at 74. The preferred implementation is that the front and rear mounts be female and male C-mounts respectively. This preference is not, however, intended to be limiting, because it is well known there are many different standards for lens mounts. Canon, for example, uses EOS mounts for most of its cameras, and many industrial lenses and cameras use T-mounts. Such other mounts may nevertheless be used in conjunction with this adapter, either at the front as a lens mount, or at the rear as a camera mount, or both, and those skilled in the mechanical arts will be readily able to extend the present principle to any suitable lens mount. A relay lens system, bracketed by 11, inside the adapter, gathers the image 65 from the attached lens that normally focuses at the original image plane represented by the dashed line 8, and relays that image to a new image plane represented by the dashed line 12 inside the camera. The relay lens system as depicted is not, however, intended to be limiting, because optical theory allows relays lens systems to be constructed in a variety of ways. The only requirements for the relay lens system are that it create a conjugate of the lenses' aperture stop—the position of which is indicated by the dashed line 59, and that it copy unaltered the original image plane represented by the dashed line 8 to the new image plane represented by the dashed line 12. Any suitable relay lens system may nevertheless be employed in the invention and those skilled in the optic arts will be readily able to extend the present principle to any relay lens system that satisfies the two requirements. The relay lens system shown bracketed by 11 is depicted with simple lenses for the purpose of illustration. In actual practice, such relay lens systems are composed of compound lenses that are achromatic with spherical aberrations corrected to produce a sharp and clear image. This depiction as with simple lenses is not intended, however, to be limiting because it is well known that more complex lenses will produce a superior image. Any quality of lens may nevertheless be employed in this invention and those skilled in the optic arts will be readily be able to employ lenses of any desired quality. A half-wave retarder 3 is placed at the conjugate of the lens aperture stop that is created by the adapter— the position of which is indicated by the dashed line 59. FIG. 39 is an exploded view of the adapter. It shows that the half-wave retarder 3 covers one-half the area of the aperture stop with the bisecting edge 5 oriented vertically or near vertically. The vertical orientation is relative to normal upright orientation of the camera to which the adapter is attached. As shown in FIG. 39, a leading polarizing filter 1 is interposed in the light path between the lens mounted at 73 and the passive half- wave retarder 3. A preferred position is between the lens mounting hole at 73 and the front element of the relay lens system 75. This position allows the front polarizing filter to protect the front surface of the front relay lens element from contaminants. Another position that is desirable is inside the lens mounting 73. In that position the front polarizer serves as a seal for the adapter as a whole, a desirable characteristic for medical use. Any position for the front polarizing filter may be employed in the invention so long as it is between the lens mounting hole and the passive half-wave retarder, and those skilled in the optic arts will readily be able to extend this principle to any acceptable position. That threads 73 are shown is not intended to be limiting because it is well known that some optical instruments image not as lenses, but as oculars for human eyes. For such instruments a clamp or physical mounting is necessary, as well as a different arrangement of optics for the relay lens 11 which will relay an aerial image to an image plane. Any such adaptation to an instrument intended for human viewing shall still be a part of this invention. That the Half- Wave Retarder Stereoscopic Light- Valve is shown is not intended to be limiting. Clearly, any of the other light-valves can be used at the aperture stop of the lens adapter. Such light-valves may include an colored filters, a Two-Polarizer Stereoscopic Light- Valve, or electro-optical shutters. While various embodiments of the present invention have been described in detail, it is apparent that further modifications and adaptations of the invention will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.

Claims: What is claimed is: 1. A system for producing a three-dimensional image of an object from an imaging signal containing imaging information relating to the object, comprising: first encoding means for encoding the imaging signal to produce an encoded imaging signal; and second encoding means, positioned at or near an aperture stop or a conjugate thereof, for encoding further a first portion of the encoded imaging signal but not a second portion of the encoded imaging signal, wherein the further encoded first portion of the encoded imaging signal has a characteristic different from the second portion of the encoded imaging signal. 2. The system of Claim 1, wherein the characteristic is at least one of polarization orientation, intensity, and wavelength distribution; the imaging signal is reflected or transmitted electromagnetic radiation; the first encoding means is at least one of an achromatic filter, a chromatic filter, a polarizing filter, an occluder, and a shutter; and the first encoding means encodes at least substantially all of the imaging signal. 3. The system of any of Claims 1 and 2, wherein the second encoding means is at least one of an achromatic filter, a chromatic filter, a polarizing filter, a retarder, an occluder, and a shutter and the second encoding means encodes from about 25% to about 75% of the imaging signal. 4. The system of any of Claims 1 to 3, further comprising at least one filtering means for passing the first and second portions of the encoded imaging signal, the first encoding means and at least one filtering means being positioned on opposing sides of the second encoding means, the at least one filtering means being at least one of a polarizing beam splitter, a plurality of polarizing filters being selected to pass electromagnetic radiation having differing polarization orientations, a plurality of chromatic or achromatic filters being selected to pass electromagnetic radiation of differing wavelength distributions, a polarization rotator, a rotating polarizer, a retarder, an occluder selected to effect the intensity of electromagnetic radiation, and a shutter. 5. The system of any of Claims 1 to 4, wherein the first and second portions of the encoded imaging signal have a common optical path. 6. The system of any of Claims 1 to 5, wherein the second encoding means is located within the lens or condenser and the first encoding means is located outside the lens or condenser. 7. The system of any of Claims 1 to 5, further comprising switching means for switching alternatively between the first polarizing orientation to pass the first portion and the second polarizing orientation to pass the second portion. 8. The system of Claim 7, wherein the switching means is at least one of a circular polarization rotator, a plane polarization rotator, a rotating circular polarizer, a rotating plane polarizer, and a variable retarder. 9. The system of any of Claims 7 to 8, wherein the switching means is at least one of a ferroelectric liquid crystal, a liquid crystal, a rotating polarizer, and a Pi cell and the second encoding means includes a joint or an edge and wherein the switching means is oriented such that in at least one operational mode of the switching means a polarizing orientation of the switching means is at least substantially parallel or orthogonal or about 45 ° to the j oint. 10. The system of any of Claims 7 to 9, wherein the switching means is at least one of a ferroelectric liquid crystal, a liquid crystal, a rotating polarizer, and a Pi cell and is oriented such that in at least one operational mode of the switching means a polarizing orientation of the switching means is at least substantially parallel or orthogonal or about 45° to a polarization orientation of the second encoding means. 11. The system of any of Claims 7 to 10, wherein the switching means has an unpowered state in which the switching means has a neutral effect on polarization. 12. A method for producing a three-dimensional image of an object from an imaging signal containing imaging information relating to the object, comprising: (a) encoding the imaging signal to produce an encoded imaging signal; (b) encoding further a first portion of the encoded imaging signal but not a second portion of the encoded imaging signal, wherein the further encoded first portion of the encoded imaging signal has a characteristic different from the second portion of the encoded imaging signal; and (c) passing the first and second portions of the encoded imaging signal through one or more further encoders. 13. The method of Claim 12, wherein the first and second portions have a different characteristic, the characteristic being at least one of polarization orientation, intensity, and wavelength distribution; the imaging signal is reflected or transmitted electromagnetic radiation; the first encoder is at least one of an achromatic filter, a chromatic filter, a polarizing filter, an occluder, and a shutter; in encoding step (a) 50% or more of the imaging signal is encoded, and at least substantially all of the encoded imaging signal has the same polarization orientation. 14. The method of any of Claims 12 to 13, wherein the second encoder is at least one of an achromatic filter, a chromatic filter, a polarizing filter, a retarder, an occluder, and a shutter; wherein the second encoder is positioned at or near an aperture stop or conjugate thereof; and wherein the first portion of the encoded imaging signal is from about 25% to about 75% of the encoded imaging signal. 15. The method of any of Claims 12 to 14, wherein the one or more further encoders on the one hand and the first encoder on the other are positioned on opposing sides of the second encoder, and the one or more further encoders are at least one of a reflector or mirror, a plurality of polarizing filters each of which passes electromagnetic radiation having differing polarization orientations, a plurality of anaglyphic filters each of which passes electromagnetic radiation portions of differing wavelength distributions, a polarization rotator, a rotating polarizer, a variable retarder, an occluder for passing electromagnetic radiation of differing intensities, and a shutter for passing electromagnetic radiation of differing intensities. 16. The method of any of Claims 12 to 15, wherein the first and second portions of the encoded imaging signal have a common optical path and in encoding step (b) the encoded imaging signal is not collimated. 17. The method of any of Claims 12 to 16, wherein step (c) includes at least one of the following steps: simultaneously passing the first and second portions through different third and fourth encoders, each of the third and fourth encoders passing at least one of (i) a different polarizing orientation, (ii) a different wavelength distribution, and (iii) differing intensities or sequentially passing the first and second portions through a common third encoder. 18. The method of any of Claims 12 to 17, further comprising a third portion of the encoded imaging signal that is different from the first and second portions. 19. The method of any of Claims 18, further comprising a fourth portion of the encoded imaging signal that is different from the first, second and third portions. 20. A system for producing a three-dimensional image of an object from an imaging signal containing imaging information relating to the object, comprising: (a) first filtering means for filtering the imaging signal to produce a filtered imaging signal; (b) retarding means for retarding only a portion of the filtered imaging signal, wherein the retarded portion of the filtered imaging signal has a different polarization orientation than the unretarded portion of the filtered imaging signal; and (c) second filtering means for filtering the retarded and unretarded portions of the filtered imaging signal. 21. The system of Claim 20, wherein the imaging signal is reflected or transmitted electromagnetic radiation; the first filtering means is at least one of a plane polarizing filter and a circular polarizing filter; and the first filtering means encodes about 75% or more of the imaging signal. 22. The system of any of Claims 20 to 21 , wherein the retarding means produces a total or net change in the polarization orientation of the first portion of about 90 degrees, is positioned at or near an aperture stop or conjugate thereof, and covers only a portion of the aperture stop or conjugate thereof. 23. The system of any of Claims 20 to 22, wherein the first and second filtering means are positioned on opposing sides of the retarding means, and the second filtering means is at least one of a polarizing beam splitter, a plurality of polarizing filters being oriented to pass electromagnetic radiation having differing polarization orientations, a plurality of chromatic or achromatic filters being selected to pass electromagnetic radiation of differing wavelength distributions, a polarization rotator, an occluder for passing electromagnetic radiation of differing intensities, and a shutter for passing electromagnetic radiation of differing intensities. 24. The system of any of Claims 20 to 23, wherein the first and second filtering means are plane polarizing filters and the first and second filtering means have substantially parallel orientations. 25. The system of any of Claims 20 to 24, wherein the second filtering means is spaced from an ocular. 26. The system of any of Claims 20 to 25, wherein the retarding means and first filtering means are positioned in a condenser or lens and the second filtering means is located outside the condenser or lens. 27. The system of any of Claims 20 to 26, wherein the first and second filtering means and retarding means are located in an adaptor removably attached to an imaging device and wherein the adaptor further includes a relay lens system positioned between the first and second filtering means and the retarding means is positioned between lenses of the relay lens system. 28. The system of any of Claims 20 to 27, wherein the retarding means is formed by applying a coating to an optically flat, transparent surface. 29. The system of any of Claims 20 to 28, wherein the retarding means has an edge coated with an electromagnetic radiation-absorptive material. 30. The system of any of Claims 20 to 29, wherein the retarding means contacts at least one of the first and second filtering means. 31. The system of any of Claims 20 to 30, wherein an edge of the coating located interiorly of the peripheral edge of the transparent surface is nonlinear. 32. The system of any of Claims 20-31 , wherein the first filtering means and retarding means are circular polarizers. 33. A system for producing a three-dimensional image of an object from an imaging signal containing imaging information relating to the object, comprising: at least one image acquisition means for acquiring an image of an object from an imaging signal, the at least one image acquisition means having a plurality of imaging pixels; and at least one matrix of filtering means corresponding to the at least one image acquisition means, located between the corresponding at least one image acquisition means and the object, for filtering, based on at least one of polarity and intensity, the imaging signal portions before receipt by the corresponding plurality of imaging pixels. 34. The system of Claim 33, wherein the at least one image acquisition means is at least one of a CCD, CMOS, and mixed phosphors and the number of filtering means is the same as the number of imaging pixels in the corresponding at least one image acquisition means. 35. The system of any of Claims 33 to 34, wherein the at least one matrix of filtering means include at least one of a polarizing filter, an achromatic filter, a retarder, an occluder, a shutter, and a chromatic filter. 36. The system of any of Claims 33 to 35, wherein each filtering means in the matrix removes substantially the same components of the imaging signal. 37. The system of any of Claims 33 to 36, wherein at least two of the matrix of filtering means are complementary optical filters. 38. The system of any of Claims 33 to 37, wherein the matrix of filtering means includes four or more filters arranged in a grid pattern, wherein at least two of the filters have different bandpass characteristics than another at least two of the filters. 39. The system of any of Claims 33 to 38, wherein each of the filtering means is an integral part of a corresponding one of the plurality of imaging pixels. 40. A method for producing a three-dimensional image of an object from an imaging signal containing imaging information relating to the object, comprising: passing the imaging signal simultaneously through a plurality of filters, at least two of the plurality of filters passing differing polarities and/or intensities of electromagnetic radiation to form a plurality of filtered imaging signal portions; and acquiring each of the plurality of filtered imaging signal portions in a corresponding plurality of pixels of an image acquisition apparatus. 41. The method of Claim 40, wherein the image acquisition apparatus is at least one of a CCD and CMOS. 42. The method of any of Claims 40 to 41 , wherein the plurality of filters include at least one of a polarizing filter, a chromatic filter, a retarder, an occluder, a shutter, and an achromatic filter. 43. The method of any of Claims 40 to 42, wherein in the passing step the imaging signal is simultaneously passed through each of the plurality of filters. 44. The method of any of Claims 40 to 43, wherein at least two of the plurality of filters are complementary optical filters. 45. The method of any of Claims 40 to 44, wherein the plurality of filters includes four or more filters arranged in a matrix, wherein at least two of the filters have different bandpass characteristics than another at least two of the filters. 46. A system for producing a three-dimensional image of an object from an imaging signal containing imaging information relating to the object, comprising: a relay lens system comprising a plurality of lenses for creating a conjugate of an aperture stop; and a filter positioned at or near the conjugate of the aperture stop in the relay lens system between at least two of the plurality of lenses for passing only a portion of the imaging signal. 47. The system of Claim 46, wherein the filter is a neutral density optical filter positioned at or near the aperture stop or the conjugate thereof. 48. The system of Claim 46, wherein the filter is a material that affects more than just the intensity of light. 49. The system of any of Claims 46 to 47, wherein the filter occludes a portion of the conjugate of the aperture stop to alter passage of a portion of the imaging signal. 50. The system of any of Claims 46 to 49, further comprising a second relay lens system comprising a second plurality of lenses for creating a conjugate of an aperture stop; and a second filter positioned in the second relay lens system at the second conjugate of the aperture stop between at least two of the second plurality of lenses for passing only a second portion of the imaging signal. 51. The system of Claim 50, further comprising a reflector or mirror to divide the imaging signal into separate fractions, with a first fraction passing through the relay lens system and filter and a second fraction passing through the second relay lens system and second filter. 52. A method for producing a three-dimensional image of an object from a signal to be reflected by or transmitted through the object, comprising: (a) encoding the signal to produce an encoded imaging signal, wherein at least substantially all of the encoded imaging signal has a common polarization orientation; (b) encoding further a first portion of the encoded signal but not a second portion of the encoded signal, wherein the further encoded first portion has a polarization orientation transverse to the polarization orientation of the second portion; and (c) contacting the first and second portions with an object to be imaged. 53. The method of Claim 52, wherein the encoding step (b) is performed at or near an aperture stop or a conjugate thereof. 54. The method of any of Claims 52 to 53, further comprising: (d) passing at least a portion of the first and second signal portions through one or more further encoders after step (c). 55. The method of Claim 54, wherein in the contacting step (c) the first and second signal portions are alternately contacted with at least one of the object and the one or more further encoders. 56. A method for producing a three-dimensional image of an object from a signal to be reflected by or transmitted through the object, comprising: (a) encoding the signal to produce an encoded imaging signal, wherein less than half or substantially all of the encoded imaging signal has a common polarization orientation; (b) contacting the first and second portions with an object to be imaged to form an imaging signal; and (c) encoding further the imaging signal. 57. The method of Claim 56, wherein in the encoding step (a) at least one of one or more color filters, one or more shutters, and one or more occluders perform the encoding. 58. The method of any of Claims 56 to 57, wherein in encoding step (a) the signal is divided into at least first and second signal portions and the first and second signal portions have different wavelength bands and/or intensities. 59. The method of Claim 58, wherein in the encoding step (c) first and second signal portions are alternately contacted with one or more further encoders. 60. An optical encoding device, comprising: a first encoding means for encoding at least a portion of an optical signal to form a first encoded signal wherein the first encoding means alters a characteristic that is at least one of a plane polarization orientation, circular polarization orientation, wavelength distribution, and intensity; and a second encoding means for encoding a portion of the optical signal or the first encoded signal to form a second encoded signal wherein the second encoding means alters a characteristic that is at least one of a plane polarization orientation, circular polarization orientation, wavelength distribution, and intensity and wherein the altered characteristic of the first encoded signal is different from the altered characteristic of the second encoded signal. 61. The optical encoding device of Claim 60, wherein the first encoded encoding means is at least one of a linear and circular polarizer and the second encoding means is at least one of a shutter, an occluder, and a colored filter. 62. The optical encoding device of Claim 60, wherein the first encoded encoding means is a linear polarizer and the second encoding means is a circular polarizer. 63. The optical encoding device of Claim 60, wherein the first encoding means is at least one of a chromatic filter and an achromatic filter and the second encoding means is at least one of a shutter, an occluder, and a polarization filter. 64. A method for processing an imaging signal to acquire an image, comprising: (a) encoding at least a portion of the imaging signal to form a first encoded signal wherein the first encoded signal has a different characteristic, that is at least one of plane polarization orientation, circular polarization orientation, wavelength distribution, and intensity, when compared to the imaging signal; and (b) encoding a portion of the imaging signal or the first encoded signal to form a second encoded signal wherein the second encoded signal has a different characteristic, that is at least one of a plane polarization orientation, circular polarization orientation, wavelength distribution, and intensity, when compared to the portion of the imaging signal or the first encoded signal and wherein the altered characteristic of the first encoded signal is different from the altered characteristic of the second encoded signal. 65. The method of Claim 64, wherein the altered characteristic of the first encoded signal is at least one of linear circular polarization orientation and the altered characteristic of the second encoded signal is at least one of the intensity and wavelength distribution. 66. The method of Claim 64, wherein the altered characteristic of the first encoded signal is linear polarization orientation and the altered characteristic of the second encoded signal is circular polarization orientation. 67. The method of Claim 64, wherein the altered characteristic of the first encoded signal is wavelength distribution and the altered characteristic of the second encoded signal is at least one of intensity and polarization orientation.

Inventors: COSTALES BRYAN, FLYNT MARCIA K, COSTALES, BRYAN, FLYNT, MARCIA, K.
Applicants: COSTALES BRYAN, FLYNT MARCIA K, SL3D INC, COSTALES, BRYAN, FLYNT, MARCIA, K., SL3D, INC.
Application year: 2000
Main classification: G02B5
IPC codes: G02B5, G02B21, G02B23, G02B27, G03B21, G03B35, H04N13