Abstract:
A viewfinder, particularly useful in a camera, is lensless but which provides a useful reticle to aid the user to properly frame the desired scene. A camera body includes a viewfinder front wall opening. Surrounding the front wall opening, on its interior surface is a concave mirror with its focus on a reticle. The reticle on an internal surface of the camera body is located at the interior face of the eyepiece opening region of the viewfinder. Incoming light at the front opening illuminates the reticle and its image is reflected by the concave mirror surface to the user&#39;s eye. In one embodiment, the front opening of the camera is a single opening larger than the rear or eyepiece opening, and in another embodiment, the front opening constitutes a series of small holes in the front wall of the camera with the surface between the holes reflectorized and acting as the concave mirror. In another embodiment also adapted particularly for zoom lens cameras, a reticle mask is included within the camera body and is adjustable with the zoom position of the taking lens to change the size of the reticle. This feature includes a pair of movable L-shaped masks, each including an L-shaped reticle and which combine to produce a variable size rectangular reticle.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part application of U.S. patent application Ser. No. 08/859,868 filed May 21, 1997, now abandoned, which is a non provisional application based upon provisional application Ser. No. 60/036,249 filed Jan. 24, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     Viewfinders find many uses and are of particular importance in cameras to aid the photographer in framing the subject. In the past, very inexpensive viewfinders have not provided an accurate means to indicate to the photographer the aim of the camera. And the most accurate and capable viewfinders, found in $70-300 point-and-shoot cameras, are too expensive for current $9-$15 single-use cameras. In the very least expensive cameras of the single-use camera type, an optical viewfinder is dispensed with, providing only a hole through the camera which provides virtually no accuracy in aiming the camera. In order to provide accurate framing, viewfinders have been used which require the use of a minimum of two lenses, to which reflective optical coatings are added (the Albada viewfinder). 
     A number of viewfinders have been devised. The following table describes various viewfinders used in simple cameras, including point-and-shoot, and single-use cameras: 
     Summary of existing low cost viewfinders: 
     
         ______________________________________     FORMS     IMAGE OFTYPE      FRAME     COMMENTS______________________________________Large hole     No        Pros: costs nothing.through camera      Cons: Frame line out of focus. Not               accurate. Acceptable for only the               least expensive cameras.Small hole in     No        Comments: Small hole near eye acts asrear wall of        a pin-hole lens.camera. Large       Pros: Image of scene and front framehole through        sharp. No motion parallax betweenfront. FIG. 1       frame and scene.               Cons: Not usable by eye-glasses               wearers. Image is dim. Has limited               field view.Reverse-  No        Pros: Relatively inexpensive.Galilean            Cons: Adds cost of lenses andViewfinder,         assembly. Lenses collect dirt, fingerFIGS. 2 and 2A      prints and scratches. Image is               minified making it harder to see               Edges of frame are out of focus. Eye               motion causes parallax errors.Albada    Yes       Comments: Created by addingViewfinder,         reflective coatings to reverseFIGS. 3 and 3A      Galilean viewfinder lenses.               Pros: Bright rectangular frame is               imaged in the scene. No motion               parallax between frame and scene.               Cons: Costs of lenses and assembly.               Lenses collect dirt, finger prints and               scratches. Image is minified making it               harder to see.______________________________________ 
    
     The reverse-Galilean viewfinder, FIG. 2, so named because it makes use of one positive and one negative lens, as Galileo used in the first telescope. However, in reverse-Galilean viewfinders, the order of the lenses is reversed which minifies the image. 
     The Albada viewfinder as illustrated in FIG. 3 uses the same lenses of the reverse Galilean viewfinder, but adds a reflective coating to the concave surface of the negative lens to act as a magnifying mirror. Also a frame or reticle is formed on the interior surface of the positive lens, usually by metal deposition. Two superimposed images are formed, (1) the lenses refract transmitted light to create a minified image of the scene, and (2) some light reflects off of the reticle forward to the concave surface of the front lens, where it is reflected (and focused) rearward to the eye. The images of the scene, and of the reticle, appear to be superimposed at a comfortable viewing distance of about 10 feet. 
     In each of these types of prior art cameras which are represented in the accompanying drawings, FIGS. 1-3, the field of view of the viewfinder is represented in the vertical dimension as the space between the lines FOV(vf) and typical images seen therein are represented by FIGS. 1A, 2A and 3A, respectively. 
     The field of view of the user&#39;s eye is, of course, larger than that of the camera viewfinder and is represented in these same figures in the vertical plane by the space between the lines FOV(eye). 
     Many cameras, including low cost point and shoot cameras provide zoom capability. For such applications, a reticle is even more important to accurately frame the photograph. 
     In the photo finishing business, a cropping aid is used which consists of a pair of planar right angled notched sheets which are movable to define a variable size exposure rectangle. These two sheets, determine the limits of the scene and crop the final reproduction. In certain complex lens type viewfinders similar planar masking devices have been used. This type of adjustment has not, heretofore, been applied to a lensless viewfinder. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The subject of this invention relates to a lensless optical viewfinder and camera with a lensless viewfinder which is not only low in cost but provides a reticle which is visible through the viewfinder when the photographer frames the portion of the scene which will appear in the processed picture. The user then can obtain properly framed photos as when using much more expensive cameras. 
     This is achieved in the preferred embodiment by employing two aligned openings in the camera case in the front and rear walls of the opaque hollow camera body. 
     The inner surface of the front opening in the camera body is surrounded by a concave mirror surface RC. On the inner surface of the rear wall of the body, surrounding the rear opening RO, is a rectangular frame defining the reticle. 
     Incident light, from the scene, is transmitted directly through the openings to the user, and also illuminates the reticle which is more reflective than the inside wall of the camera surrounding the rear opening. 
     The concave mirror, surrounding the inside of the front opening and outside of the viewfinder field of view FOV(vf), reflects and focuses an image of the reticle to the eye of the user who sees the image of the reticle as if it is part of the scene in front of the camera. 
     The viewfinder of this invention optionally eliminates the need for any refractive material such as lenses or transparent windows in the viewfinder opening. 
     In the case of a zoom lens camera, the same basic lensless viewfinder is formed in the camera body with its front opening and concave mirror. The reticle, however, is formed in two parts, on diagonally opposite corners of the rear opening, described below. 
     Within the camera body in the viewfinder optical path are a pair of L-shaped sliding masks which define a variable sized opening. These plates are coupled to the zoom-adjustment mechanism to change their spacing and thus to change the size of the reticle opening to correspond to the field of view of the camera lens. 
     By comparison with the prior viewfinders discussed above: 
     
         ______________________________________HINES&#39; LENSLESS VIEW FINDER    FORMS    IMAGE OFTYPE     FRAME     COMMENTS______________________________________HINES&#39;   Yes       Pros: Bright rectangular frame islensless           imaged in the scene. No lenses usedperimeter-         or associated cost. No motionframe              parallax between frame and scene.viewfinder,        Image of scene remains full size as inFIGS. 4, 5-7       the most expensive SLR&#39;s. Costs              approximates that of using no              viewfinder. Quality suitable for more              expensive cameras as well.              Cons: ---HINES&#39;   Yes       Pros: Bright rectangular frame islensless           imaged in the scene. No lenses usedperforated-        or associated cost. No motionframe              parallax between frame and scene.viewfinder,        Image of scene remains full size as inFIGS. 8 and 9      the most expensive SLR&#39;s. Costs              approximates that of using no              viewfinder. Quality suitable for more              expensive cameras as well. Provides a              wider field of view of the scene than              the reticle, to aid composition.              Cons: Scene brightness reduced. Edges              of holes creates some diffraction.              Accommodates a range of reticle sizes,              required by zoom cameras.HINES&#39;   Yes       Pros: camera provides accurate framelensless           lines, of a size matching that of thevariable focal     zoom lens, without cost of multilength             element zooming viewfinder lenses.viewfinder         Cons: eye relief is slightly reduced              for wide-angle position.All HINES&#39;    Yes       Pros: No image minification.lenslessviewfindersabove______________________________________ 
    
     This viewfinder is not limited to cameras but may be used in other applications, as well. The single use camera is a prime candidate for its application because of its low cost, ease of incorporation in those products and the fact that it provides a reticle image in the field of view of the user&#39;s eye without the use of any refractive elements and without any image minification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     This invention may be more clearly understood with the following detailed description and by reference to the drawings in which: 
     FIG. 1 is a transverse sectional view through a prior art lensless viewfinder having a large opening at the front of a camera and a small eyepiece opening at the rear and a user&#39;s eye with the field of view of the viewfinder FOV(vf) and the field of view of the user&#39;s eye in the vertical plane defined by limit lines; 
     FIG. 1A shows the view through the viewfinder of FIG. 1 with typical soft-focus indistinct frame lines; 
     FIG. 2 is a transverse sectional view through a conventional prior art reverse-Galilean viewfinder illustrating the light path and fields of view of the viewfinder and of the user&#39;s eye similar to FIG. 1; 
     FIG. 2A shows the minified view through the viewfinder of FIG. 2 with soft-focus indistinct frame lines; 
     FIG. 3 is a view similar to FIG. 1 of the prior art Albada type viewfinder; 
     FIG. 3A shows the minified view through the viewfinder of FIG. 3 with superimposed sharply focused reticle; 
     FIG. 4 is a lateral cross sectional view through a camera incorporating my invention including the fields of view of the viewfinder and the user&#39;s eye and the light paths of incident light and the reflected light path from the reticle to the concave mirror, and the reflected reticle image to the users eye in dashed lines; 
     FIG. 4A shows the unminified view through the viewfinder of FIG. 4 with sharply focused reticle; 
     FIG. 5 is an interior perspective view of the preferred embodiment of my invention of FIG. 4; 
     FIG. 6 is a partial perspective view of the embodiment of FIGS. 4 and 5; 
     FIG. 7 is a partial perspective view similar to FIG. 6 of an alternate embodiment of my invention; 
     FIG. 7A shows the unminified view of the scene, with sharply focused reticle and slight localized attenuation of the scene due to the radial struts; 
     FIG. 8 is an interior perspective view similar to FIG. 5 of another embodiment of my invention employing a different form of front opening; 
     FIG. 9 is a partial perspective view similar to FIGS. 6 and 7 of the embodiment of FIG. 8; 
     FIG. 9A shows the unminified view of the scene with sharply focused reticle; 
     FIG. 10 is a partial perspective similar to FIGS. 6 and 7 of an alternate embodiment of my invention; 
     FIG. 11 is a lateral cross-sectional view taken slightly off center to clearly show reflected light passing through a perimeter opening through a camera of the embodiment of FIG. 10 and with a user wearing glasses; 
     FIG. 12 is a perspective view of a camera with the viewfinder of my invention partly broken away for clarity; 
     FIG. 13 is a horizontal sectional view of a camera with zoom capability which also employs my lensless viewfinder invention with corresponding changeable reticle size; 
     FIG. 14 is simplified exploded front elevational view of the variable aperture elements of viewfinder of FIG. 13; 
     FIG. 15 is a reduced size top plan view of a camera of this invention in the wide angle lens and viewfinder position; 
     FIG. 16 is a fragmentary front elevational view of the changeable aperture feature of my lensless viewfinder on the camera of FIG. 13 when in a wide angle configuration; 
     FIG. 17 is a reduced size top plan view of a camera of this invention in the normal focal-length lens and viewfinder position; 
     FIG. 18 is a fragmentary front elevational view of the changeable aperture feature of my lensless viewfinder on the camera of FIG. 13 when in a normal focal-length configuration; 
     FIG. 19 is a reduced size top plan view of a camera of this invention in the telephoto lens and viewfinder position; and 
     FIG. 20 is a fragmentary front elevational view of the changeable aperture feature of my lensless viewfinder on the camera of FIG. 13 when in a telephoto configuration. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Disclosed in the drawing, FIGS. 4, 5-7, 8-9, is my basic viewfinder, which uses no lenses, but which forms a bright image of a reticle at the distance of the scene to be photographed. 
     Transmitted light is represented in FIG. 4 with solid line ray traces TL, and reflected light RL which forms the image of the reticle RT are shown as dashed lines. Note that there are two superimposed optical paths, as in the Albada viewfinder of FIG. 3, for the view of the scene, and the bright-line reticle. My proposed viewfinder uses reflective optics which can be molded as part of the front and rear walls, FW and RW respectively, of the camera body CB [FIGS. 4-6]. Therefore, the viewfinder of my invention requires no additional parts compared to the prior art lensless viewfinder of FIG. 1. The bright image of the subject is shown surrounded by a clear bright reticle in FIG. 4A. 
     FIG. 4 also illustrates the field of view of a typical human eye as defined by the lines FOV(eye) and the field of view of the viewfinder FOV(vf) as it is defined, both in the vertical plane. A similar relationship exists in the horizontal plane. 
     It should be noted that the optical path through the viewfinder in the field of view of the viewfinder as defined above is free of any refractive or other optical elements, i.e., an open hole defined by the normal opaque camera body. This means that in the manufacture of cameras employing the invention, the camera body defines the entire viewfinder and it provides a reticle image inside the field of view of the user&#39;s eye FOV(eye) and is superimposed upon the field of view of the viewfinder FOV(vf), achieving the same results as more complex and expensive lens viewfinders. Unseen directly by the user is the actual reticle RT located on the inside surface of the rear wall RW, or at least on a front facing surface inside the viewfinder cavity of the camera body CB. 
     There is no directly exposed transparent surface which may become soiled or scratched, and no subassembly operations for the viewfinder are required in manufacturing. At most, a metalizing operation will be required for the concave mirror and reticle of the viewfinder. 
     Visible to the viewfinder user is the concave mirror surface RC on the front wall FW or on a rear facing surface surrounding the front opening FO of the viewfinder. This concave mirror RC provides the reticle image viewed by the user without any minification of the image seen through the viewfinder. 
     In one embodiment of this invention shown in FIGS. 8 and 9 and described below, the front opening FO is actually a number of small openings with the mirrored inner surface on the front wall surrounding the array of small openings. 
     FIG. 5 shows an interior perspective view of the viewfinder portion of the camera body CB, showing the reticle RT formed around the rear opening, RO, and the concave mirror RC molded as a spherically-curved surface on the inside face of the front opening FO. FIG. 6 shows an exterior of the viewfinder portion of the camera body CB. The reticle/mirror combination RT/RC forms a sharply-focused image of the reticle RT so that it appears to be fixed on and placed into the scene in accordance with well known camera design practice. 
     The viewfinder of my invention is basically an open hole through the front and rear walls of the camera body. The optical elements of the viewfinder exist only at the perimeters of the openings on the front and rear walls of the camera and outside of the field of view FOV(vf) of the viewfinder. A concave generally spherical surface, is molded on a protrusion on the interior face of the front camera wall FW. The concave surface is preferably flashed with aluminum or other metallizing material to make it a highly reflective surface RC. 
     The reticle RT is formed similarly on the interior surface of the rear wall RW of the camera body CB, by depositing a reflective frame (the same operation used to create the reflective coating RC on the interior of the front wall FW and incidentally, to create the reticle on the positive lens an Albada viewfinder). 
     It should be noted that minification of an image, in prior art viewfinders, is not a user advantage, but done for engineering reasons, to be able to use small viewfinder lenses and maintain the field of view which matches that of the camera taking lens. A one-to-one, or full size, image, before my invention has usually been implemented in only the single lens reflex cameras, using a complex and expensive lens and prism system or in the least expensive single use cameras which have not provided sharply focussed frame lenses. 
     The simple prior art hole-type viewfinder of FIG. 1 is incapable of providing a sharply-imaged frame of reference. Use of the reverse-Galilean or Albada viewfinders of FIGS. 2 and 3, respectively, precludes 1:1 size imaging because they use lenses which inherently minify the image. 
     A variation of the Albada viewfinder could be made in which the front and back glass or plastic elements were curved meniscus elements which had no refractive power; however, this would save no cost over the traditional Albada design. 
     My proposed lensless viewfinder does not result in minification; however, provides a sharply imaged frame of reference. Thus, my lensless viewfinder provides both simplification and improvement as compared with other basic viewfinders, and costs virtually the same as the simple through-hole type viewfinder, i.e. nothing, except reflective metallizing; however it creates a rectangular frame which appears to be superimposed on the scene. 
     The reticle RT shown in these drawings, FIGS. 4 and 5, is a raised surface, with the thought that the raising the surface would facilitate printing it with white, or coating it with aluminum to increase its reflectivity. However, the reticle RT can be raised or flush depending on the physical size of the camera and the optical requirements of the viewfinder. A precise smooth surface produced in the injection molding process of the opaque camera body may provide sufficient reflectivity to provide a usable reticle image without metallizing. 
     It may be desirable to have a viewfinder which shows slightly more of the scene than will actually be photographed, to help the photographer compose the picture. This lensless viewfinder can be configured with the spherical mirror frame in the form of a thin strip generally surrounding the front opening FO and supported on struts S, within a larger opening FO in the front wall FW, as shown in FIG. 7 which is an exterior of the viewfinder portion of the camera body CB. The result of this embodiment is illustrated in FIG. 7A in which a portion of the scene appears surrounding the reticle. 
     Another embodiment of my invention, shown in FIGS. 8 and 9, takes the form of the substantially spherical mirror FSM, on the interior face of the front wall FW of camera body CB, being perforated with hundreds of small holes H, approximately 1 mm across, which creates the front opening FO. The holes H, are close enough to the eye to be out of focus and provide an apparent continuous images of the transmitted scene and of the reflected reticle RT. The ratio of holes H to surrounding front wall area FW can be varied to increase the transmitted light, or the reflectance of the rear reticle RT. 
     All described techniques are aided by the small scale of the optics and supports relative to the diameter of the pupil in the eye. The eye sees the focused image of the projected reticle RT overlapping the scene within the out-of-focus inner edge of the front window FW. However, the structure of the front optics (support struts S in FIG. 7, and small holes H in FIGS. 8 and 9, etc.) are out of focus and do not appreciably interfere with the use of the viewfinder. 
     In each of the figures of the drawings showing these embodiments, only the viewfinder portion of the camera is illustrated for clarity of understanding. A typical arrangement in a single use camera is illustrated in FIG. 12. The camera taking lens assembly, the shutter, and film advance, all of which are in accordance with established practice, and constituting image captive means are contained within the camera body CB and sealed from ambient light from the viewfinder reaching the film by internal walls, side wall SW and lower wall LW provide this sealing function. Recognizing that current developments in cameras, digital storage of images replace the conventional film and film advances. Any form of image capture means, film or electronic storage is usable with this invention. 
     FIGS. 10 and 11 show an embodiment where greater eye relief for the user is provided, particularly useful for eye glass wearers. In this case the reticle RT is supported on radial reticle supports RS of FIG. 10, similar to the mirror supports S of FIG. 7. To minimize obscuration of the reflected image of reticle RT and supports RS, they are molded radial to the optical axis. 
     This insures minimum observation by the radial supports of the viewed scene. 
     This allows the user to move the eye without being restricted to view only through the rear opening, and still see the reflected image of the reticle. The reticle is so thin and out of focus as to be un-noticeable. 
     The reticle supports RS are struts or ribs which extend generally radially with respect to the center of the rear opening. As shown in FIG. 10, the reticle supports RS are preferably located at each corner of the rear opening and mid points of the reticle top, bottom and sides. The reticle RT itself comprises a thin rectangular frame with its major cross section generally paralleling the dashed reflective light ray lines so as to minimize interference with the view of the reticle image outside of the reticle in the perimeter opening PO. This aids the user in framing the subject of the scene whether or not wearing eye glasses. 
     When this invention is applied to a more complex camera such as one which provides various aspect ratios or zoom operation, there is a need to change the reticle size to provide a matching field of view through the viewfinder, again, without the use of lenses. This is accomplished by the embodiment of this invention as illustrated in FIGS. 13-20. 
     Refer now to FIG. 13 in combination with FIG. 14 to see a variable-reticle lensless-viewfinder zoom-lens camera generally designated C including a camera body CB with a front wall FW, a rear wall RW, a lens assembly ZL in the front wall FW and containing a suitable holder for a film cassette FC and suitable film advance mechanism (unshown) to advance film F behind the lens ZL for exposure upon operation of a suitable shutter(unshown) under the control of shutter release SR of FIG. 12. The design of taking lens assemblies, shutter mechanisms and film advances for cameras are well known and will be selected in accordance with well known design principles in the photographic industry therefore are not illustrated here. 
     The viewfinder of this embodiment is contained within the opaque camera body CB in the chamber defined by the exterior walls of the camera body CB and the interior side wall SW and lower wall LW with a rear opening RO in the camera rear wall RW, a front opening FO in the camera front wall FW, and a concave mirror RC similar to the embodiment of FIG. 4. The reticle RT of FIGS. 4-6 is, however, replaced by an adjustable or movable reticle which changes in size with changes in focal length of the lens assembly ZL. 
     The reticle of this embodiment is, preferably, formed from two relatively movable masks, designated for convenience based upon their relative location in the embodiment of FIGS. 14, 16, 18 and 20 as the bottom left reticle BLR on the bottom left mask BLM, and the top right reticle TRR located on the top right mask TRM. The two masks BLM and TRM are each notched to define a variable size rectangular opening when superimposed and moved in diagonally opposing directions of the double ended arrow in FIG. 14. The L-shaped inner edges of the notches of the respective masks BLM and TRM facing the front opening FO, have a bright or reflective surface similar to the corresponding surfaces of the embodiment of FIG. 4 to be distinguishable from the normal black background of the interior of the camera body CB. The masks BLM and TRM each include a clearance hole GS and an actuator pin slot APS. The actuator pin slots APS each engage a respective actuator pin left LAP or right RAP of FIGS. 13, 16, 18 and 20 on a rotating disc RD to move the two masks BLM and TRM simultaneously in opposite directions to open or close the reticle formed by the visible reticle surfaces BLR and TRR. 
     Movement of the actuator pins LAP and RAP is accomplished since they are connected to a regulating disc RD which is rotatably mounted for rotation within a recessed cylindrical cavity in the rear wall RW of the camera body CB. The regulating disc RD is coupled to the lens mechanism by any one of a number of gear or linkage mechanisms. Suffice it to say, the masks BLM and TRM are both coupled to the zoom adjustment of lens assembly ZL for coordinated movement therewith. Further, the overall position of the mask mechanism can be collectively shifted to compensate for parallax errors when close focusing, and differentially shifted to accommodate various aspect ratios. 
     In FIG. 13 the eye of the user is indicated adjacent to the rear opening RO, and ambient light, from the scene to be photographed, is indicated by the parallel lines TL with the outermost two lines indicating the light rays striking the reticle surfaces BLR and TRR. Light reflected from the surface RC of the concave mirror CM from the reticle and to the user&#39;s eye is illustrated by the thin dashed lines of FIG. 13. 
     The operation of this invention in a zoom or selective focal length camera is illustrated in FIGS. 13-20. FIGS. 15, 17 and 19 are simplified top views of the same camera C in a wide angle, normal and telephoto adjustment, respectively. Each of these figures show the matching horizontal fields of view for the camera taking lens ZL and for the viewfinder. The change in focal length of the taking lens is indicated by the degree of extension of the lens while the adjustment of the viewfinder is totally within the camera C as described above in connection with FIGS. 13 and 14. More precise showing of the change of positions of the masks BLM and TRM and the change in sizes of the reticle is illustrated in FIGS. 16, 18 and 20. In these figures, the masks BLM and TRM are shown as secured for sliding movement under tabs T which preferably are molded integrally as a part of the rear wall RW of the camera body CB. Movement of the masks BLM and TRM is in the direction of the arrows of the respective drawings. The relative position of the regulating disc RD and its extent of rotation for each lens position is indicated by the position of the actuator pins LAP and RAP. 
     An alternate method of coupling the viewfinder reticle adjustment mechanism to the lens assembly is shown in FIGS. 16, 18 and 20. It includes an actuator arm A with one end coupled to actuator pin LAP and the other end including an attachment means for coupling arm A to the lens zoom adjustment mechanism(unshown) to be moved in the direction of the arrows as the lens zooms. 
     In comparing FIGS. 16, 18 and 20, note the change in extent of overlapping of the masks BLM and TRM, with corresponding change in size of the reticle of the viewfinder. 
     The above described embodiments of the present invention are merely descriptive of its principles and are not to be considered limiting. The scope of the present invention instead shall be determined from the scope of the following claims including their equivalents.