Stereoscopic microscope

An observation device including an intermediate tube that houses two relay optical systems and an image rotator, each relay optical system having an exit axis that is substantially parallel to the exit axis of the other relay optical system, and an ocular tube that houses two image formation optical systems and two eyepiece optical systems. The intermediate optical tube has a connecting portion that connects to a connector at the top of a stereoscopic microscope body at one end and is rotatably connected to the ocular tube at the other end, the ocular tube is extendable from, and collapsible into, the intermediate tube over a movement range in the direction of the exit optical axes of the pair of relay optical systems, and exit pupils of the pair of relay optical systems are arranged near a middle position of the range of movement of the ocular tube.

This application claims the benefit of priority of JP 2002-271963, filed Sep. 18, 2002, the subject matter of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Stereoscopic microscopes of the prior art provide surgeons with a magnified view of a surgical area and have improved the efficacy of surgery. Such microscopes are used in surgical operations by neurosurgeons, otolaryngologists, as well as ophthalmologists. Today, so called micro surgery, which uses a microscope for surgery, is advanced and precise. The surgical microscope is designed so that it may provide images of the surgical area from various directions, and surgery is performed under the observation of two persons, an observer who has primary responsibility for the surgery (hereinafter referred to as the first observer) and an observer (hereinafter referred to as the second observer) who has the responsibility of supporting the first observer in order to improve the safety of the operation.

Many surgical microscopes of the prior art are limited in that the azimuthal directions that the first and the second observer peer into the surgical microscope must differ by 90 degrees or 180 degrees. This sometimes is inconvenient in that, at times, only one observer is able to actually observe the operation site, depending on the direction of the optical axis of the objective lens of the surgical microscope relative to the surgical area.FIG. 17(a) shows an example of a first observer1and a second observer2that observe a surgical area4from azimuthal directions that differ by 180 degrees. The optical axis of the objective lens of the surgical microscope3in this case is vertical.FIG. 17(b), on the other hand, shows an example where, using a similar surgical microscope5as that inFIG. 17(a), the first observer7is able to observe the surgical area6with the optical axis of the objective lens tilted from the vertical position. However, in this instance, it is difficult for the second observer8to comfortably peer into the microscope eyepiece. This problem occurs, for example, in the microscope shown inFIG. 1of Japanese Examined Patent Publication S47-41473 and in the microscope shown inFIGS. 2-4of Japanese Examined Utility Model Publication S55-39364. For most prior art surgical microscopes, the difference in azimuthal angles α between a primary observer and a secondary observer who is positioned on either side of the primary observer, is 90 degrees, as indicated inFIG. 1of the present application. On the other hand, for a secondary observer who faces the primary observer, the difference in azimuthal angles α is 180 degrees.

The value of α is variable for the microscope disclosed inFIG. 1of Japanese Laid-Open Patent Application H10-5244. The surgical microscope disclosed therein is shown inFIG. 18of the present application. Because an optical path splitting means11is provided between the objective optical system9and the first observation device10used by the first observer, the microscope's size must be increased and the distance between the bottom surface12of the surgical microscope and the eyepiece lens13is increased, thereby decreasing the distance from the bottom surface12of the surgical microscope to the surgical area14(hereinafter termed the ‘working distance’).

For the microscope shown inFIG. 18, the second observation device15that provides observation images to the second observer is arranged directly below the first observation device10. This causes both the space19(illustrated inFIG. 19, wherein the microscope is labeled16) that is located below the eye level18of the first observer17, when the second observer is positioned opposite the first observer to be narrowed. Referring toFIG. 20, it also causes the space21to the right of the first observer23when the second observer is to the right of the first observer, to be narrowed. This causes a problem in that a treatment tool24(FIG. 20) held by the first observer23is more likely to come into contact with the second observation device22of the surgical microscope20, thereby causing an inconvenience during surgery.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a stereoscopic microscope such as a surgical microscope that enables a plurality of observers to observe the same microscope observation image of an observation object at the same time. More specifically, the present invention provides an easy-to-use surgical microscope for use by two observers that has the ability to make the difference in azimuthal angles for two observers peering into a surgical microscope variable while not diminishing the working space beneath the second observation device.

DETAILED DESCRIPTION

The stereoscopic microscope of the present invention includes a first connector for connecting a first observation device for use by a first observer and a second connector for connecting a second observation device for use by a second observer to a body of a stereoscopic microscope. The stereoscopic microscope also includes the following components: an objective optical system, and a pair of zoom optical systems which enables at least a first observer and a second observer to simultaneously observe the same microscope observation image of an observed object. The second connector is arranged at the same height on the stereoscopic microscope body, or at a higher position, as that of the first connector, the second observation device is connected so as to be capable of revolving about a central rotation axis of the second connector, and the angle between the rotation axis and the optical axis of the objective optical system in the region that lies between the object and the microscope body is ±15° or less.

According to the invention, the difference in azimuth angles at which a first observer and a second observer peer into a stereoscopic microscope can be made to be variable. And, since the second observation device is not arranged lower than the first observation device, a problem of the working space beneath the second observation device being diminished for surgery, as in the prior art, does not occur.

Furthermore, it is preferred that the rotation axis of the second observation device and the axis of the objective optical system in a region between the observation object and the main body of the stereoscopic microscope be parallel.

The light flux of one of the two zoom optical systems is split by a pupil splitter into two beams, each having somewhat different parallax, and emitted as a pair of light fluxes to the second observation device. In addition, the light fluxes of both of the zoom optical systems are split off by a beam splitter and directed to the second observation device. The second observation device receives the light fluxes split off by the beam splitter when the second observation device is positioned generally opposite the position of the first observer and it rotates the orientation of the images so that the observer is presented with a view of the surgical area having a proper orientation for the second observer's azimuthal position about the surgical area.

FIG. 1is an explanatory diagram of a stereoscopic microscope according to this construction, viewed from above, with the second observation device removed from the second connector. The four light fluxes27,28,29, and30that are conveyed within the second connector26are shown exiting the stereoscopic microscope main body25. From among these four light fluxes, the two light fluxes29and30that do not have diagonal hatch lines are the light fluxes that provide the microscope image with a correct image orientation to a second observer33or34who peers into the microscope at angles of ±90° laterally in relation to the first observer32who observes through the first observation device31. The two light fluxes27and28shown with diagonal hatch lines are the light fluxes that provide a correct image orientation of the microscope images to the second observer35who peers into the microscope at an azimuth angle opposite to that of the first observer32. The term “correct image orientation” means that the orientation of the observation image of the surgical area as seen through the microscope by the second observer and the orientation of the surgical area as seen directly from the standing position of the second observer match.

Further, the second observation device is able to receive two light fluxes from among the four light fluxes illustrated, and to rotate these light fluxes as needed so as to provide a correct image orientation according to the standing position of the second observer. Thus, it is possible for the second observer, by rotating the second observation device, to always observe a correct image orientation even when observing from any of the three possible viewing positions (90° to the left, 90° to the right, or in a direction 180° relative to the direction of observation of the first observer).

Two light fluxes from among the four light fluxes at the second connector are obtained by splitting a light flux from one of the zoom optical systems. To accomplish this, a pupil splitter is used which is positioned near an image of the exit pupil as relayed by a relay optical system. According to the present invention, the stereoscopic microscope main body provides four light fluxes that are directed to the second observation device while using only two zoom optical systems.

According to one construction, a normal line to a contact plane that is formed as the top surface of the first connector is slanted toward the first observer, and the second connector is positioned on the microscope body in the opposite azimuthal direction. According to this construction, as shown inFIG. 2, because the first connector36has its surface normal slanted toward the first observer37, the first observer is positioned near the first connector36. This is advantageous in allowing the first observer to be closer to the surgical area by observing through a first observation device41that is slanted, rather than a first observation device that is horizontal, in that the first observer can be nearer the observation object39. Furthermore, the second connector164is positioned nearby the first connector36. This enables the distance40between the surgical area which is the observation object39and the second observer38to remain small. Further, the first connector36is positioned relatively closer to the optical axis of the objective lens than is the second connector164. This is also advantageous in allowing the first observer to be closer to the surgical area by observing through a first observation device41and to treat the surgical area more easily.

The four light fluxes are emitted towards the second observation device58(FIG. 4) after being reflected an even number of times by a plurality of reflecting optical elements inside the microscope body60. As shown inFIG. 3, the second observer by using the second observation device53can always view microscope images with a correct image orientation even if the second observation device is rotated somewhat from α=90 degrees to either side or if the second observation device is rotated to the position (α=180 degrees) facing the first observer. Some additional plus or minus rotation is permitted so long as parts of two light fluxes, such as51and52from among the four light fluxes, enter the two optical system openings54and55of the second observation device53.

In addition to providing rotation at the rotation axis of the second connector, the second observation device may have a rotation component that is rotatable about a different axis. Where the angle made by the rotation axis of the rotation component and the axis of the objective optical system in a region between the observation object and the microscope body is within a range of 35° up to and including 55°, where all four light fluxes that enter into the second observation device reach the rotation component, and where the rotation component accepts only two of the light fluxes at a time from among the four light fluxes, the light fluxes that are accepted may be changed by rotating the rotation component. This construction enables the angle α, namely the difference in azimuth angle that the first observer and the second observer peer into a stereoscopic microscope, to be variable.

The second observation device may include an intermediate optical tube that houses a pair of relay optical systems and a single image rotator, and an eyepiece optical tube that houses a pair of image formation optical systems and a pair of eyepiece optical systems. The intermediate optical tube connects with the second connector at one end and with the eyepiece optical tube at the other end. Further, the eyepiece optical tube has the ability to extend and retract in the optical axis direction of the exiting light fluxes from the pair of relay optical systems housed by the intermediate optical tube, and both of the exit pupil positions of the pair of relay optical systems housed by the intermediate optical tube are arranged near an interim position within the range of the extending and contracting movement of the eyepiece optical tube. According to this construction, the second observer can move the position of the eyepiece optical tube within the range of the extending and contracting movement, thus enabling greater freedom of positioning of the second observer in the use of the microscope. Further, since the exit pupil positions of the pair of relay optical systems are arranged near to the middle position of the extending and contracting range, and since the pair of image formation optical systems housed by the eyepiece optical tube take in the light fluxes with very little eclipsing of these light fluxes, even if the second observer moves the eyepiece optical tube to another position within the range of movement, a microscope image with substantially no eclipsing can be observed.

Various embodiments for the stereoscopic microscope of the present invention will now be provided with reference to the drawings.

FIGS. 4 and 5illustrate Embodiment 1, withFIG. 4being an exploded view of some of the components andFIG. 5showing the stereoscopic microscope of this embodiment fully assembled, with the second observation device rotated to three different azimuthal positions relative to the first observation device. As shown inFIG. 4, a first connector57connects the first observation device56to the stereoscopic microscope and a second connector59connects the second observation device58to the stereoscopic microscope. The second connector59is positioned on top of the stereoscopic microscope body60. The stereoscopic microscope body60is supported by the support200and the second connector59is separated from the first connector57. Rather than the second connector being positioned on the microscope body60lower than the first connector, the position of the second connector is higher and farther from the observation object61than is the position of the first connector57.

Further, as shown inFIG. 5, the second observation device63is connected to the second connector62with the ability to rotate about a rotation axis64. Furthermore, the rotation axis64of the second observation device63and the optical axis67of the objective optical system in the region from the observation object65to the microscope body66are constructed so as to be parallel. According to this construction, as seen inFIG. 5, the second observer68observing a microscope observation image by using the second observation device63has the ability to observe the microscope image from various angles in relation to the first observer70who observes the microscope observation image using the first observation device69. Also, since the second observation device63is arranged on the microscope body at a position that is higher than that of the first observation device69, the space from the eyepiece73of the first observation device to the bottom surface74of the microscope body66is not lengthened. By maintaining the space from the observation object65to the bottom surface74of the microscope body, there is no narrowing of the working distance directly below the stereoscopic microscope. In addition, the space75near the lateral vicinity of the microscope body66that is below the eye level71of the first observer and in front of the first observer70is not narrowed by the second observation device63. The stereoscopic microscope of the this embodiment, as described above, enables work to be safely performed beneath the microscope by maintaining a sufficient space between the bottom of the microscope body and the surgical area. This embodiment also enables the difference in azimuth angles at which two observers may peer into a stereoscopic microscope to be varied.

The construction of a stereoscopic microscope according to Embodiment 2 will be explained usingFIG. 6.FIG. 6is an exploded view of some of the components of Embodiment 2. A first connector79is provided for connecting the first observation device78for use by the first observer77and a second connector81is provided for connecting the second observation device80with the ability to rotate about an axis, thereby enabling the second observer to observe in different azimuthal directions (assuming the axis of rotation is vertical). Further, a normal line to a contact plane that is formed as the top surface of the first connector79is tilted toward the first observer77, and the second connector81is positioned on the microscope body76in the opposite azimuthal direction and near to the position of the first connector. In addition, the light fluxes82,83,84, and85exit from within the second connector81, two of which may then selectively enter the second observation device80, depending on the rotation angle of the second connector.

FIG. 7illustrates the optical arrangement inside the stereoscopic microscope main body shown inFIG. 6. Light flux emitted from the observation object86passes through the objective optical system87and is deflected by the optical path reflecting element88. A first reflective surface (i.e., the reflective surface of optical path reflecting element88) deflects light paths from the objective optical system to a substantially horizontal direction. This light flux is then separated into two light fluxes by passing through left and right zoom optical systems89,89after which the light fluxes are each relayed by a respective front lens group90and passed into a pair of first relay optical systems. The first relay optical systems are formed of various prisms92. A second reflective surface (i.e., the lower reflective surface of the prisms92) then deflects the light paths upward, and a third reflective surface (i.e., the upper reflective surface of the prisms92) then deflects the light paths to a substantially horizontal direction. Thus, the first through third reflective surfaces form a folded optical system and the pair of zoom optical systems is arranged within the folded optical system. After exiting the first relay optical systems, each left and right light flux passes through a respective rear lens group91and is then emitted from the first connector93toward the first observation device (not shown).

Further, the light fluxes94,94exiting the first relay optical systems are split by a beam splitter96which is in the optical paths and directly below the second connector95. Thus, two light fluxes97and98are split off from light fluxes that otherwise would enter the first connector93and instead are directed to the second connector95. As illustrated inFIG. 7, the first and second connectors are arranged on opposite sides of the optical axis of the objective optical system as viewed in a direction of the horizontal optical path of the folded optical system.

In addition, a light flux that passes through one of the first relay optical systems has a portion split off by a beam splitter99that is arranged in the optical path of one of the first relay optical systems. The light flux100subsequent to being split off is guided to a pupil splitting prism101using a plurality of prisms. The pupil splitting prism101, which forms the light fluxes104and104by splitting the light incident thereon, is arranged near to the position where the exit pupil of one of the zoom optical systems is relayed. Further, the light fluxes104and104are further relayed by a second relay optical system which is formed of a front lens group102, a rear lens group103, as well as various prisms and mirrors in each light path so as to become two fluxes105and106that exit from the second connector95toward the second observation device (not shown). Accordingly, a total of four light fluxes exit from the second connector95.

The two light fluxes105and106from among these four light fluxes are the light fluxes that provide the microscope image in the correct image orientation to the second observer when the second observer is positioned to the left or right of the first observer ( i.e., when α=90 degrees), and the remaining two light fluxes97,98are the light fluxes that provide the microscope image in the correct image orientation to the second observer when the second observer is positioned facing the first observer (i.e., when α=180 degrees). In addition, all four light fluxes97,98,105, and106exit from the second connector95after being reflected an even number of times by a plurality of prisms and mirrors within the stereoscopic microscope main body.

As used in the claims, the term “first leading optical system” corresponds to, inFIG. 7, the optical system composed of the beam splitter99and all other optical elements arranged on the optical path branched by the beam splitter99and the beam splitter96, the term “second leading optical system” corresponds to, inFIG. 7, the optical elements between the objective lens87and the second connector95, and the term “third leading optical system” corresponds to, inFIG. 14, the prism162.

According to the construction of the stereoscopic microscope main body described above, the space between the surgical area which is the observation object and the second observer can be maintained short when a first observer and a second observer use a stereoscopic microscope facing each other. Thus, access to the surgical area is improved for the second observer. Furthermore, since four light fluxes are provided and two of these are selected for observation by the rotational position of the second observation device, a compact arrangement is made possible for a stereoscopic microscope main body (i.e., only two, not four, zoom optical systems are required).

A description will now be given of the second observation device of this embodiment with reference toFIG. 8. The second observation device107is comprised of an intermediate optical tube108and an eyepiece optical tube109, and the eyepiece optical tube connects to the intermediate optical tube in a manner that allows the eyepiece optical tube to rotate, as indicated by the double-headed arrow. This allows the second observer to tilt his head to the left or right while viewing into the eyepiece optical tube. Further, the intermediate optical tube108houses a single image rotator (not shown) and a pair of relay optical systems (not shown).

FIG. 9(a) is a side view of the optical components within the interior of the intermediate optical tube of this embodiment, andFIG. 9(b) shows a top view thereof. Only two light fluxes111and112from among the four light fluxes111,112,113, and114exiting the second connector110of the microscope body enter the pair of relay optical systems composed of prisms115and116, lenses117and118, and the erection optical systems119,119. By rotating the second observation device roughly 90° about the rotation axis165, the light fluxes111and112will be blocked from entering the second observation device and the light fluxes113and114will no longer be blocked and will enter the second observation device. In this manner, the intermediate optical tube of the second observation device accepts only two light fluxes at a time from among the four light fluxes that exit from the second connector, and the light fluxes that are accepted for viewing by the second observer can be switched by rotation of the second observation device about the rotation axis165(which corresponds to the rotation axis64shown inFIG. 5)to a different observation position.

In addition, the single image rotator120housed within the intermediate optical tube is arranged so as to transmit simultaneously both light fluxes from the pair of relay optical systems. The single image rotator is rotated at a ratio of 1/2  of the rotation amount of the eyepiece optical tube121. By combining the construction of the second observation device given above and the construction of the microscope body described above, it becomes possible to always observe an image that has a proper image orientation. Furthermore, when the second observation device is rotated from these three positions within a range of angles where the pair of relay optical systems housed within the intermediate optical tube takes in the light fluxes, the second observer can observe images with the correct image orientation. Further, by the effect of the image rotator, it is possible for the second observer to view an observation image with substantially no eclipsing of the light flux even if the eyepiece optical tube is rotated, thereby increasing the freedom in the observation positions of the second observer. The term “ocular optical system” as used herein corresponds to the optical system composed of the optical elements116through120inFIG. 9(a) and includes the lens(es) in the eyepiece optical tube121.

FIGS. 21-24show an example of the construction of the image rotator and the mechanism that can be used in the microscope according to this invention for rotating the image rotator at a ratio of one-half the rotation amount of the eyepiece optical tube. The structure is similar to that disclosed in Japanese Laid-Open Patent Publication H6-109977.

FIG. 21is an example of a housing181containing an image rotator optical system with an eyepiece lens tube182having a binocular optical system attached.FIGS. 22(a) and22(b) show horizontal and vertical cross-sectional views, respectively, of the interior of the housing181. In the figures, a fixed tube183is provided having cylindrical steps and is designed so that two left and right observation optical axes L1and L2of light fluxes from an observation object (not shown) can pass through the interior of the fixed tube.

A linear cam groove C that is parallel to the observation optical axes L1and L2is formed on a large-diameter section183aof the fixed tube183. A first tube184that is fit outside the fixed tube183on the large-diameter section183ais freely rotatable and includes a cam groove C2which intertwines with the cam groove C1. The eyepiece lens tube182(FIG. 21) is attached by a retaining member (not shown) to the first tube184so that, when the eyepiece lens tube182is rotated, the first tube184rotates with it as a unit.

As labeled inFIG. 22(b), a stopper ring185is screwed into the first tube184and secured to the fixed tube183via a washer W1. A cover186is attached just outside the first tube184. A second tube187that is equipped with an image rotator optical system, is fit so as to be freely rotatable inside the large-diameter section183a, and a cam groove C3which intertwines with the cam groove C1is formed on the outer circumference of the second tube187.

FIG. 23is a cross-sectional view of the front interior of the housing181. As shown inFIG. 23, the second tube187has a U-shaped, rotator holding unit188awhich holds an image rotator prism188. The image rotator prism188, which is fixed within the U-shaped, rotator holding unit188aby a flat-head screw (guide bar)191, receives and transmits the left and right light fluxes traveling along the observation optical axes L1and L2.

A cam pin190(FIG. 22(b)) that is screwed into a moving ring189is simultaneously engaged by the cam grooves C1, C2and C3. A guide bar191is screwed into the fixed tube183so that its axis is oriented parallel to the observation optical axes L1and L2. The guide bar191guides the moving ring189which surrounds the guide bar. A washer W2is placed in a thrust-direction space between the fixed tube183and the second tube187, and a washer W3is placed within a space of the first tube184that extends over both the second tube187and the fixed tube183, with the effect of preventing the first and second tubes184and187from moving in the thrust direction.

FIG. 24is a view of cylindrical cams of the image rotator as seen from the direction of arrow A inFIG. 22(b). If the angles at which the cam grooves C2and C3intertwine with the linear cam groove C1are denoted as θ and γ, respectively, and the radius of the first tube184and the second tube187shown inFIG. 23are denoted as R1and R2, respectively, the following relationship exists between θ and γ, namely,
tan γ=2(R2/R1)tan θ.

First, when the eyepiece lens tube182is rotated, the first tube184also rotates together with the eyepiece lens tube182as one body. At this time, the cam pin190which engages with the cam groove C2moves only parallel with the observation optical axes L1and L2as a result of being constrained by the cam groove C1and the guide bar191. By the movement of the cam pin190, the second tube187, which holds the image rotator prism188inside, rotates by half the rotation angle of the first tube184to which the eyepiece lens tube182is attached.

Next, a detailed description will be given of different optical systems.FIG. 10shows the components of the second relay optical system of Embodiment 2 that is formed of a front lens group122and a rear lens group123. The lens elements124and125, shown with cross-hatching, are formed of anomalous dispersion glass. Use of anomalous dispersion glass in these lens elements minimizes the deterioration of optical performance of the second relay optical systems.

Table 1 below lists the surface number #, the radius of curvature R of each surface, the on-axis spacing D between surfaces, as well as the index of refraction Ndand the Abbe number νd(both at the d-line) of the lens components of the second relay optical systems.

The optical axes of the second relay optical systems pass through the geometric centers of each of two parts of the exit pupil, which two parts are formed by dividing the pupil of the zoom optical system in half by the pupil splitting prism and relaying the divided pupils by the first relay optical system. For this reason, in comparison to the relay optical system128through which the optical axis127passes the center126of the exit pupil prior to splitting as shown inFIG. 11(a), the relay optical system131through which the optical axis130passes the geometric center129of the exit pupil subsequent to being split in half as shown inFIG. 11(b) can be made to have a smaller lens diameter, thereby resulting in the ability to make the stereoscopic microscope main body more compact.

FIG. 12shows the relay optical system components housed by the intermediate optical tube of the second observation device. The relay optical system is formed of a front lens group132and a rear lens group134. The front lens group includes a front lens component and a rear lens component. The rear lens group is formed of various lens elements, as shown. The lens elements shown with cross-hatching, namely, lens element133in the front lens group and the lens elements135,136and137of the rear lens group are formed of anomalous dispersion glass. Use of anomalous dispersion glass in these lens elements minimizes the deterioration of the optical performance of the relay optical system within the intermediate optical tube of the second observation device.

Table 2 below lists the surface number #, the radius of curvature R of each surface, the on-axis spacing D between surfaces, as well as the index of refraction Ndand the Abbe number νd(both at the d-line) of the components of relay optical systems housed by the intermediate optical tube.

A description of the stereoscopic microscope of Embodiment 3 will be given usingFIGS. 13 and 14.FIG. 13shows the exterior of the second observation device. A second observation device138has a single rotation component140that rotates about a rotation axis145that makes an angle of 50° with the optical axis of the objective optical system in the region between the object and the microscope body. At any one time, two of the four light fluxes141that exit the second connector139enter into the second observation device138, pass through the optical system housed in the fixed component142, and arrive at the rotation component140.

FIG. 14shows the arrangement of components of the optical system of the second observation device according to this embodiment. The fixed component142houses a prism162which passes all of the four light fluxes from the second connector to the rotation component140. The rotation component140houses prism143that reflects each light flux so as to redirect the light fluxes. The rotational component140also houses a pair of relay optical systems (each formed of two separated lenses161), an erection optical system163, and an image rotator144.

According to this construction, as shown inFIG. 15, the angle α, as measured between the azimuthal viewing directions between the first observer148and the second observer149, can be made variable by rotation of the rotation component. Thus, the present construction allows additional rotation of the rotation component147(which often was previously restricted to three positions) of the second observation device146, thereby increasing the freedom of choice in selecting an observation position of the second observer. Furthermore, the second observer can always view stereoscopic microscope observation images with correct image orientation, as long as the second observation device is rotated to positions within a limited range in which the light fluxes which enter the lenses161are not completely eclipsed by the rotation of the rotation component about the positions where a equals ±90 or 180 degrees.

FIGS. 16(a) and16(b) show the second observation device150according to Embodiment 4 of the present invention, withFIG. 16(a) being a top view, andFIG. 16(b) being a side view. The second observation device150is composed of an intermediate optical tube152for housing a pair of relay optical systems151,151(each formed of separated lens components), and an eyepiece optical tube155for housing a pair of image formation optical systems153,153and a pair of eyepiece optical systems154,154. In addition, the intermediate optical tube152connects to the second connector157of the stereoscopic microscope156at one end, and it connects to the eyepiece optical tube155at the other end. The eyepiece optical tube155has the ability to extend and contract in the direction of the exit optical axes158,158of the pair of relay optical systems151,151housed by the intermediate optical tube152. Also, both exit pupil positions159,159of the pair of relay optical systems housed by the intermediate optical tube152are arranged in the middle position within the extending and contracting movement range.

According to this construction, the second observer160can move the position of the eyepiece optical tube155within the movement range along the optical axis of the pair of relay optical systems housed by the intermediate optical tube152, thereby making it possible for microscope observations to be performed with more freedom of position. In addition, since the exit pupil positions159,159of the pair of relay optical systems are arranged near to the middle position of the movement range, the pair of image formation optical systems housed by the eyepiece optical tube receive the light fluxes, which exit the pair of relay optical systems housed by the intermediate optical tube, in a state of substantially no eclipsing. Therefore, the second observer can observe a microscope image with substantially no eclipsing by moving the eyepiece optical tube to any of the many and various positions available.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention. Rather, the scope of the invention shall be defined as set forth in the following claims and their legal equivalents. All such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.