Microscope

Abstract: In an optical microscope, particularly an optical microscope having optics which include divergent beams of light being transmitted to the eyepieces, a facility for display or teaching is provided by replacing a conventional eyepiece with an eyepiece (21) which includes a light tube (22 a ) and respective inlet and outlet lenses (26) and (27), said light tube (22 a ) accommodating a beam splitter such as a semi-silvered mirror (29) to deflect a portion (30) of light passing through tube (22 a ) laterally towards a camera (32).

Description: This invention relates to optical microscopes. Many kinds of binocular ophthalmic microscope/slit lamps exist which have parallel eyepieces. The geometry of the optical system in such microscopes, and their physical construction lends itself easily to the addition of a teaching arm or video recording/display system. In order to incorporate such a system it is only necessary to interpose a beam-splitter, incorporating a 45° partially-reflective mirror in the light path between the objective and the eyepiece lenses. Diverted light is fed to a camera, such as a video camera, and can be recorded on film or displayed on a screen or diverted to a teaching tube as required. This latter facility is very useful for teaching and other purposes when two or more persons wish to view the image from the microscope. There is, however, a certain class of microscope wherein such an easier modification is simply not possible. This type of microscope is the microscope which has convergent eyepieces. In such a microscope the eyepieces are disposed at a mutually-inclined angle of about 9°. This is the angle at which the eyes normally are disposed when working at a desk or performing comparable functions. This is the most comfortable angle for the eye and such microscopes are notoriously easy to use, being much less likely to cause eye strain than parallel-eyepiece microscopes. Many such microscopes are in use because of their benefit, but unfortunately they suffer from the drawback that their optical system has a geometry which does not lend itself to the interposition of a beam-slitter within the microscope body as does the geometry of a parallel eyepiece microscope. Accordingly, convergent eyepiece microscopes have not, heretofore, been amenable to the addition of a display facility. One particularly very common form of convergent eyepiece microscopeis manufactured by Haag Streit and is known as their "900" microscope. This lack of a display facility on such convergent eyepiece microscopes is a disadvantage. Many are in use and it would be of great advantage to provide such a facility for existing microscopes. Further, as will be apparent from Figures 1 and 2, the previously known method of modifying the microscope requires that the microscope has a body constructed to be seperable. This is not always the case, further this prior method requires that the microscope and its installation be such as to allow a significant increase in the overall length of the microscope. This is not always possible when the microscope is part of a larger arrangement. The moving of the eye pieces can make the apparatus much more difficult to use. Further, parts which need to be added to the microscope to provide the beam-splitting facility tend to be quite large, relatively complicated and expensive. It is relatively easy to include a teaching facility including an extra eyepiece together with a video camera or recorder microscopes which have parallel eyepieces. The reason for this is that the light passing to the eyepieces travels generally along parallel paths. Thus, increasing these path lengths by including a beam splitter (shown in Figure 2 of the aforesaid application) does not significantly effect the optics of the system. Further, parallel eyepiece microscopes have relatively simple optics, light from the objective lens passing through an intermediate lens and then directly to the eyepieces. Particular problems arise in relation to binocular microscopes which have divergent eyepieces. The desirability of such microscopes has been previously described in the aforesaid application and it should be emphasized here that in such a microscope there is, essentially, a "binocular" effect in that the light to each eyepiece passes via a prism disposed in an individual casing which connects each eyepiece to the main body of the microscope. This physical mode of construction is a serious bar to the inclusion of a beam splitter/camera facility. In addition, the light travelling to the eyepieces in such a microscope is generally converging. Thus, if the individual housing, or the main housings, were split to include a beam splitter, it would be possible to divert light outwardly of the microscope to a second eyepiece, or to a camera, but it would be extremely difficult for the existing eyepiece to focus on the virtual image which is formed between the eyepiece and the remaining optics. Changing the light path length by introduction of a separate beam splitter portion would require considerable modification of the optics, as well as considerable physical modification of the arrangement. Many hundreds of such instruments are in use, and (as most users would confirm) the modification of such a microscope to include a teaching/camera facility would be a significant advance. The basic idea of using an eyepiece which includes a beam splitter to direct a portion of light towards a camera and/or a second, observers, eyepiece can be understood quite easily from the foregoing. In putting this proposal into practice certain problems have arisen. Firstly, by introducing extra length in the eyepiece to accommodate the beam splitter and side tube, it proved to be impossible to have the eyepiece lenses focussed on the virtual image formed within the eyepiece. This tended to mean that the exit pupil of the light from the ocular lens was spaced considerably (perhaps 15 to 20 mm) away from the said lens. This made the device extremely difficult to use, as the user's eye was exposed to considerable amounts of stray light from the sides. Such a feature also made it very unusual to use, because it was completely different from most optical apparatus wherein the eyepiece has to be disposed virtually against or touching the eye surround. A second problem was that the light coming from the beam splitter, being, as has been said, divergent, could not be satisfactorily focused on the CCD chip. This was because the distance between the beam splitter and the chip could not be made sufficiently long to ensure that the light came into focus at a reasonable distance. The apparatus still worked, but only about one third of the image available fell onto the chip. This resulted in reduced intensity of light on the chip and also reduced the field of view on the chip camera by a two thirds. A further problem in carrying the idea into effect was that the light reaching the camera, having been deflected by the beam splitter was a mirror of the view seen by the observer. This meant that the electronic image generated by the camera needed to be reversed before being viewed by a third party, or in a video in order that the sense of movement could be the same in each case. Whilst left to right reversal of a video picture is theoretically simple and straightforward, in connection with the (desirably) simple electronics to be used in a compact system, the use of electronic reversal leads to added expense. Further, as the basic data coming from the camera needs to be reversed, the provision of the reversing facilities does tend to introduce unacceptable costs, and unacceptable distortion (in the sense of loss of quality) of the eventual image. As a further disadvantage, the provision of a beam splitter in only one eyepiece, makes the light received by that eye of the observer which looks into that eyepiece of lower intensity than the light coming from the other eyepiece. This leads to a severe loss of stereoscopic vision between the eyes. This is an effect which seems to occur in the brain, and although not completely understood at present, seems to result from the brain's inability to recognize that the two eyes are seeing the same subject when one eye is receiving light of a different intensity from the same image. The effect seems to be similar to the Paulfich effect which has been observed in comparable apparatus. It is an object of the present invention, therefore, to provide a divergent optic microscope wherein the above described disadvantages are obviated or minimised. According to a first aspect of the invention there is provided a microscope eyepiece (21,35) including a distal lens, (26, 43) an ocular lens (27, 38), a light tube (22a, 36) surrounding the light path from the distal lens (26, 43) to the ocular lens (27, 38), characterised in a beam splitter (29, 41) positioned in the light path between the distal lens (26, 43) and the ocular lens (27, 38) to divert a portion (30) of the light passing through the tube (22a, 36) laterally of the tube (22a, 36), and in a camera (32, 46) mounted to receive said diverted light (30). The camera is preferably supported by the eyepiece structure. The eyepiece can be incorporated in a chamber carried by the tube. The chamber carrying the camera can be a short tube branching from the eyepiece tube. Preferably the camera is in the form of a transducer able to receive said light beam and convert it into electrical signals representative of the light in the beam, said signals being capable of display by a cathode ray television screen or comparable display to give a picture comparable to the view seen by an observer looking into the exit lens of the eyepiece. The beam-splitter can be a partially reflective mirror extending across the eyepiece tube. The camera can be a microchip camera. The camera can include on a microchip a plurality of charge couple devices. The camera is preferably so small as to be capable of easy support by the eyepiece without significant deformation thereof. The camera preferably has an area less than 25mm by 25mm, and desirably less than 10mm by 10mm. A camera having a receving screen of charge coupled devices measuring some 6mm by 6mm has been found satisfactory. Such a device is extremely light and small and can be incorporated in a microscope eyepiece with little difficulty. The output signal from the camera can be led to a television screen for observation or to a video recorder for future reference. The eyepiece can be incorporated in a microscope and the invention includes a microscope fitted with an eyepiece aforesaid. Preferably the microscope is a convergent eyepiece microscope. Normally a microscope will require only one eyepiece of the invention. However, if desired it could be provided with two eyepieces of the invention which would be capable of displaying two images. By appropriate display it is possible that a three-dimensional view could be displayed to several persons. For example, each camera could feed a single screen and observers could be provided with apparatus compelling their one eyes to observe one screen only and their eyes to observe the other screen only. A divergent lens can be provided at the end of the eye piece remote from the ocular lens to move the virtual image formed within the eyepiece to a position nearer to the ocular lens. A convex lens can be provided in the light path between the beam splitter and the camera. A pair of eyepieces for a divergent optic microscope, can comprise one eyepiece as aforesaid, and the other eyepiece of the set including a neutral density filter arranged and adapted to reduce the intensity of light passing directly through the second eyepiece. A second reflector can be provided between the beam splitter and the camera. This ensures that both the pupil of the observer facing the eyepiece of the invention, and the camera receive the same picture and there is no need for electronic inversion of the image displayed on the screen. Preferably, in the set of eyepieces the second eyepiece is optically identical to the first eyepiece apart from the beam splitter. The camera and the second reflector can be accommodated in a tube lying parallel to the eyepiece and connected thereto by a short lateral tube. The lens between the beam splitter and the mirror can be disposed in the lateral tube. When the divergent lens is provided at the end of the eyepiece remote from the ocular lens to move the virtual image formed within the eyepiece to a position nearer to the ocular lens, and a second reflector and a convex lens is provided to deflect the light from the beam splitter to a film camera, the convex lens can lie between the beam splitter and the reflector and can be selected so that the image formed on the film of the film camera body is of a size compatible with the film size. The invention will be described further, by way of example, with reference to the accompanying drawings wherein; Figure 1 is a schematic view illusting a parallel eyepiece conventional microscope; Figure 2 is a view of the microscope of figure 1 but modified by the addition of a beam splitter and a camera; Figure 3 is a view comparable to that of figure 1 but showing a convergent eyepiece microscope; Figure 4 is an enlarged cross-sectional view illustrating an eyepiece of the microscope of figure 3; Figure 5 shows an eyepiece of the invention; Figure 6 is a schematic cross-sectional view through a preferred eyepiece of the invention; Figure 7 is a comparable view through a companion eyepiece of the invention; and Figure 8 shows a modification of the construction of figure 6. Referring now to figures 1 and 2, it will be seen that a conventional parallel eyepiece microscope (10), has an objective lens system (11), a body (12) and two parallel eyepieces (13) before the observer's eyes (14). When modified in accordance with figure 2 a beam-splitter (15) including one or two 45° semi-silvered mirrors deflects a proportion of the light down a side tube (16) to a conventional television camera (17) which can pass a signal to a monitor and/or video recorder. As these devices are perfectly conventional they have not been illustrated. Second side tube (16a) can lead to a teaching arm (16b). Figure 3 illustrates a microscope (18) which has convergent eye pieces (19). The nature of the body (20) and the complicated geometry of the light path within the body (20) (not shown) makes it impossible to modify the body in the way in which the body (12) of the microscope (10) has been modified in figure 2. Figure 4 shows an eyepiece of this microscope (18), having a tube (22), an inlet lens (26) and an outlet lens (27). This problem can, however, be overcome using the eyepiece (21) of the ivnention as shown in figure 5. The eyepiece (21) consists of a tube (22a) about 22mm in diameter. Like the conventional eyepieces (19) tube (22) is a sliding fit within a socket (23) within walling (24) of the body (20). Tube (22) can be secured by a screw (not shown) or the like. The screw normally secures the conventional eyepiece (19). The tube (22a) includes a distal lens (26) and an outer lens (27) adjacent the observer 28. Lenses 26 and 27 constitute the ocular lens of the microscope. Within the tube 22 a is disposed a 45° partially silvered mirror 29 which forms a beam-splitter. Other beam- splitting devices can be used, but a semi-silvered mirror is cheap, conventional and convenient. Deflected light 30 from the mirror 29 passes into a chamber 31 which is disposed laterally of the tube 22 and which mounts a microchip charge coupled device camera 32. The camera 32 has a sensitive receiving field consisting of large numbers of charge coupled devices formed on a small chip of semi-conductor material, each device being coupled to circuitry within the chip. The camera 32 produces a signal at its outlet (depicted schematically by terminals 33). Signals from terminals 33 can be passed to a monitor, display screen and/or video recorder in conventional manner. It will be appreciated that this improved eyepiece 21 of the invention can be used in place of an existing eyepiece 19, the modification to the actualmicroscope 18 being negligible. The eyepiece is a simple and convenient way of converting a convergent eyepiece microscope to allow for demonstration, teaching and the like. Of course, the invention is not limited to use in a convergent eyepiece microscope and can be used with conventional parallel eyepiece microscopes if desired. Referring now to Fig. 6, it will be seen that a second embodiment of eyepiece 35 of the invention includes a pair of co-axial tube sections 36 and 37. Inner tube 36 is of the same diameter as a conventional eyepiece and can be inserted into a divergent optic microscope in the aperture which is formed to receive a conventional eyepiece. In conventional manner the eyepiece includes an ocular lens 38 and a distal lens 39 which lenses are effective to direct light from a virtual image formed by the primary optics of the microscope into the observer's eye 40. Between the lenses 38 and 39 is disposed a beam splitter which can have any practical form, such as a prism, mirror or the like, but is preferably in the form of a semi-silvered mirror 41. To accommodate the splitter 41 and the lenses 38 and 39, it is necessary that the total length of the tube 36 and 37 exceeds that of a conventional tube usually (depending on the magnification) by some 15 or 20mm. This has the effect that the lens system constituted by lenses 38,39, is spaced further from the usual virtual image position (illustrated at Ia). The lens system 38,39 would, therefore, normally focus the image Ia in the plane 42. It would be possible for the observer to use the microscope in this condition, but he would have to place his pupil in the plane 42. This is an extremely uncomfortable position and is contrary to almost all optical use, wherein the pupil of the eye is placed very close to the ocular. There is the further problem that incident light can enter from the sides and interfere with the observation. In order to overcome this severe problem, we have found it desirable to include a divergent lens 43 at the inner end of tube 36. This modifies the light coming from the primary optics of the system to produce a virtual image at the position shown at Ib. The position of the image Ib is such that the optical system 38,39 can focus the light on the pupil of the observer's eye 40 whilst disposed close to the ocular 38 in conventional manner. It should be noted here that it is theoretically possible to overcome this defect by altering the characteristics of lens 38 and 39. However, any serious alteration of lens 39 affects the optic path between the virtual image and the camera (to be later described) and is undesirable. Further, it is desired that lenses 38 and 39 be conventional in power and disposition in order that they do not unduly change the nature of the overall optical system far from its original design parameters. The addition of the lens 43 is a cheap, simple and unexpectedly effective way of compensating for the increased length of the eye piece 35 caused by the provision of the beam splitter 41. As mentioned previously, the beam splitter 41 is arranged to divert 50% of the light laterally outwards of the tube 37 into a lateral tube 44. Tube 44 connects with a short camera tube 45 which extends parallel to the tubes 36 and 37. Within the camera tube 45 is arranged a CCD chip camera 46 whose ouput can be taken via leads 47 and circuitry 48 to a television monitor and/or video recorder 49 (all of which are illustrated schematically). Camera tube 45 also includes a 45° mirror 50. This has the affect that the light reaching the camera 46 has been reflected twice and therefore produces an image on the camera which is the same as that seen by the observer. This has significant effects in saving the costs of electronic inversion and in the inevitable loss of quality which electronic inversion can cause in small and compact electronics. As has been previously mentioned above, the power and disposition of the lenses 38 and 39 is effectively set by the overall optics of the system and it is undesirable to alter them too greatly. With the arrangements shown within the tubes 36 and 37 the light reaching camera 46 via the beam splitter and mirror would not be completely focused on the The light path is too short. It would, of course, be possible to make the lateral tube, or the camera tube very long, but this is physically undesirable and would make the whole apparatus ungainly and difficult to use. With the physical dimensions of the various tubes as shown in Fig. 6, only about one third of the light issuing from the beam splitter 41 would impinge upon the camera 46 and therefore only one third of the field of view would be seen by the camera. To obviate this problem without going to the above described lengths of inordinate physical sizes, I have found that it is a remarkably neat and simple solution to provide a convergent lens 51 in the light path between the beam splitter 41 and the camera 46. The lateral tube 44 can provide a very convenient mounting for the lens 51. Fig. 7 illustrates a companion eyepiece 52. When the eyepiece 35 is used as one eyepiece of a divergent binocular optic microscope the eyepiece 52 can conveniently be used as the other eyepiece. Eyepiece 52 has tubes 53 and 54 comparable to tubes 36 and 37 as well as ocular and distal lens 55 and 56 identical to lenses 38 and 39. Between the lenses 55 and 56 is disposed a neutral density filter 55 whose function is to reduce the intensity of light exiting via ocular 55 to be generally the same as that exiting from the ocular 38, thereby compensating for the light diverted by the splitter 41. This ensures that the intensity of the image received by the observer's eyes is generally the same and therefore three dimensional vision is not impaired. The invention is not limited to the precise details of the foregoing and variations can be made thereto. Fig. 8 shows a further modified eyepiece 55 in accordance with a further aspect of the invention. This eyepiece is similar to the eyepiece of Fig. 6 except that instead of lens 51, a comparable lens 56 is provided nearer to the outer tube 37. Further, camera tube 45 is modified to incorporate a T piece 57 which has an annular fitting 58 which is complementary to the annular lens fitting of a conventional 35 mm single lens reflex camera 59. The camera 59 is perfectly conventional and is not described in any detail. The fitting 58 can involve a screwed connection or a bayonet connection. The positioning and strength of the lens 56 are chosen so that an image is formed on the film of the camera body 59 which is of size comparable to the film and which is in focus in the film plane. It will be appreciated that tube 45 and 37 do not have to be parallel. By appropriate selection of the reflector in the place of the mirror 50 (for example a prism) the camera body 59 could be mounted in any convenient position. However, by having the tube 49 parallel to the tube 37 is possible to use virtually the same metal ware as used in the embodiment of Fig. 6, thus saving production costs. It will be seem that the camera is upside down in Fig. 8. This is so that the prism mounting 60 can be accommodated without fouling the tube 36. it is, of course, a simple matter to invert the print after it has been formed. In dotted lines in Fig. 6 is shown an alternative position 51a for the lens 51. For example, although the various lenses have been shown as simple single element lenses, it would be appreciated that one or more thereof can be compound lenses to compensate for lens aberrations. One or more of the lenses can be interchangeable to provide an eyepiece of varying magnification. Alternatively, the powers of the various lenses can be chosen in a particular eyepiece to give a particular magnification. A further separate eyepiece can have different lenses to have a different magnification. Many further modifications are possible within the scope of the invention.

Claims: A microscope eyepiece (21,35) including a distal lens, (26, 43) an ocular lens (27, 38), a light tube (22a, 36) surrounding the light path from the distal lens (26, 43) to the ocular lens (27, 38), characterised in a beam splitter (29, 41) positioned in the light path between the distal lens (26, 43) and the ocular lens (27, 38) to divert a portion (30) of the light passing through the tube (22a, 36) laterally of the tube (22a, 36), and in a camera (32, 46) mounted to receive said diverted light (30). An eyepiece as claimed in claim 1 characterised in that the camera is supported by the eyepiece structure (31, 45). An eyepiece as set forth in claim 1 or 2 characterised in that the camera (32) is carried in a chamber branching from said light tube (22a). An eyepiece as claimed in claim 2 or 3 characterised in that said camera (32) is in the form of a transducer able to receive said light beam (30) and convert it into electrical signals representative of the light in the beam, said signals being capable of display by a cathode ray television screen (49). An eyepiece as claimed in any of claims 1 to 4, characterised in that said beam splitter (29,41) is a partially reflective mirror extending across said light tube (22a, 36). An eyepiece as claimed in any of claims 1 to 5, wherein said camera (32, 46) is a microchip camera including a plurality of charge-coupled devices. An eyepiece as claimed in claim 6, wherein said camera (32, 46) has a receiving screen of charge-coupled devices measuring less than 10mm by 10mm, preferably 6mm by 6mm. An eyepiece as claimed in any of claims 1 to 7, characterised in that a divergent distal lens (43) is provided to move the virtual image (Ia) formed within the eyepiece to a position (Ib) nearer to the ocular lens (38). An eyepiece as claimed in any of claims 1 to 8, characterised in that a convex lens (51, 51a, 56) is provided in the light path between the beam splitter (41) and the camera (46, 60). A pair of eyepieces for a microscope, one of the eyepieces being as claimed in any preceding claim, and characterised in that the other eyepiece (52) of the pair includes a neutral density filter (57) arranged and adapted to reduce the intensity of light passing directly through said other, eyepiece (52) and exiting from the ocular lens (55) of said other eyepiece (52). An eyepiece as claimed in any of claims 1 to 9 characterised in that a second reflector (50) is provided between the beam splitter (41) and the camera (46, 59). A pair of eyepieces as claimed in claim 10 characterised in that said second eyepiece (52) is optically identical to the first eyepiece (21, 35). An eyepiece as claimed in claim 11 characterised in that the camera (46) and said second reflector (50) are accommodated in a tube (45) lying parallel to the eyepiece (35) and connected thereto by a lateral tube (44). An eyepiece as claimed in claim 13 in connection with claim 9 characterised in that said convex lens (51) is positioned between said beam splitter (41) and said second reflector (50) and is disposed in said lateral tube (44). An eyepiece as claimed in claim 9, characterised in that the camera is a film camera (59) and the convex lens (56) is selected so that the image formed on the film of the film camera is of a size compatible with the film size. An optical microscope having two eyepieces each having an optical axis, the optical axes of the two eyepieces being disposed at an angle relative to each other, characterised in that one of said eyepieces is as claimed in any of claims 1 to 9, 11 or 13 to 15. An optical microscope having two eyepieces each having an optical axis, the optical axis of the two eyepieces being disposed at an angle relative by each other, characterised in that the eyepieces constitute a pair as claimed in claim 10 or 12.

Inventors: GUTRIDGE JOHN, GUTRIDGE, JOHN
Applicants: GUTRIDGE JOHN, GUTRIDGE, JOHN
Application year: 1990
Main classification: G02B21
IPC codes: G02B21