CA1098352A

CA1098352A - Magnifying optical system

Info

Publication number: CA1098352A
Application number: CA295,266A
Authority: CA
Inventors: Robin J. Freeman
Original assignee: VISION ENGINEERING Ltd
Current assignee: VISION ENGINEERING Ltd
Priority date: 1977-01-20
Filing date: 1978-01-19
Publication date: 1981-03-31
Also published as: CH619791A5; DE2801262A1; SE7714278L; JPS5393024A; SE425579B; FR2378293B3; FR2378293A1; DE2801262C2; GB1586701A

Abstract

ABSTRACT OF THE DISCLOSURE

In an optical apparatus, particularly magnifying apparatus such as microscopes or screen projectors, a magnified image of an object is produced on a focal plane, in which focal plane is rotated a planar device on two parallel surfaces of which device are provided respective arrays of parallel grooves such that the cross-section through each surface and transverse to the groove length is in the form of a plurality of arcs, The grooves in one surface are arranged transversely to the grooves in the other surface. A field lens system is arranged to receive light from the said device. The effect is to provide an enlarged pupil both when the device is at rest and when it is rotating.

Description

10~8352 This invention relates to improvements in optical apparatus, particularly magnifying apparatus such as microscopes and screen projectors.
It is known that the exit pupil of a normal microscope has a limited diameter so that a viewer's eye must be in a closely defined position.
If the head is moved transversely the image is lost and if the head is moved towards and away from that position the field size is affected.
In the prior art the problem has been overcome by scanning the conventional exit pupil in space by means of moving elements placed at the image focal plane of the instrument to provide an enlarged pupil. In all prior art arrangements, when the moving elements are stationary, no pupil enlargement occurs, and in this condition if the viewer's eye is coincident with this stationary pupil a full field will be observed.
In our prior Canadian Patent No. 894,336 issued February 29, 1972 we described an optical system incorporating at the image focal plane of the optical device a movable multilenticular element, that is, a planar element comprising a multiplicity of tiny circular lenses. This differs from the other prior art devices in that with the multilenticular elemer.t in a static condition an enlagred exit pupil is maintained, but an incomplete field is viewed by the observer. Rotation of said element results in the viewing of a complete field and the retention of the enlarged pupil. There are always a multiplicity of lenticules in the field of view.
However, when the lenticules are circular, it has been found that there may be some degradation at the centre of the image, caused by flat areas on the eiement between the lenticules. This can be particularly disadvan~
tageous in a stereoscopic instrument.
The present invention relates to an improved optical apparatus.
According to one aspect the invention is an optical system for viewing an object comprising optical means arranged to provide in a focal plane a magnified image of an object; a generally planar device arranged in said focal 3~ plane, there being on two generally parallel surfaces of the device respective arrays of grooves such that the cross section through each surface and trans-verse to the groove length is in the form of a plurality cf arcs, the grooves 10~8;~52 in one surface being arranged transversely to the grooves in the other surface; means to rotate the device with said surfaces in or near to the focal plane; and a field lens system arranged between said planar device and the exit pupil to receive light from said device.
The grooves on each surface are preferably parallel to each other, but other arrangements are possible. For instance, the grooves on one surface may be concentric circles and those on the other surface may be radial.
The field lens system is arranged so that in the absence of the grooved device the system would produce an exit pupil such that, if the eye of a viewer were coincident with said exit pupil, a full field would be seen.
The effect of the grooved device is to provide an enlarged pupil both when the device is at rest and when it is rotating.
Usually the grooved device will comprise two flat discs, each grooved on one surface and with the grooved surfaces in contact and in said focal plane. However, the discs may alternatively be slightly curved so as to compensate for field curvature due to other parts of the optical system.
The grooves may be such that each grooved surface comprises a plurality of half cylindrical protrusions or depressions; alternatively there may be alternate protrusions and depressions when the arcuate cross section may be of sinusoidal form. In any arrangement there are effectively no flat areas on the grooved surface. The system may be such that both discs are transparent or one disc may be transparent and the other may have a reflective surface.
Usually the discs will be arranged so that the grooves in one surface are perpendicular to the grooves in the other surface.

lQ-"8352 In the aeeompanying drawings, Figure 1 illustrates a eonventional eyepieee lens, and the invention will be deseribed by way of example with referenee to:-Figure 2, whieh shows in seetion parts of two rotatable grooveddises, Figure 3, whieh shows sehematieally the optieal effeet of one part of one of the dises of Figure 2;
Figures 4 and 5~ which show sehematieally refleeting and trans-mitting microseopes aeeording to the invention;
Figure 6, whieh shows an optieal beam splitting arrangement; and Figures 7 and 8, whieh show sehematieally reflecting and trans-mitting stereoscopic mieroseopes aceording to the invention.
In Figure 1, an eyepieee lens system 10 reeeives light from the limiting aperture 12 of an objeetive 13, and provides at a focus 14 a eon-ventional exit pupil whieh, in a high magnifieation system sueh as a mieroseope, is about 2 mi]limetres or less in diameter. The eye of an observer using the eyepieee direetly must be positioned so that the pupil of the eye eoineides with the exit pupil at 14.
Figure 2 shows parts of two eireular plane discs, 16, 18, rotatable about a eommon axis 20. The surfaee of disc 16 is grooved so as to have alternate protrusions 22 and depressions 24 of substantially part-cylindrical form and sueh that a seetion through the surface is a eontin-uous, approximately sinusoidal curve as shown, typically of a pitch of less than 1 millimetre. The disc 18 has identical grooves which are arranged parallel to the plane of the Figure, that is, perpendieular to the grooves in disc 16. The grooved surfaces are in contact.
Figure 3 illustrates one part-cylindrical protrusion 22 in disc 16. Reference 14 indicates the position of the conventional exit pupil provided by the eyepiece lens system 10 in Figure l; the eyepiece lens ~0'3835Z

system forms a real image at the plane of the disc 16. The protrusion 22 acts as a cylindrical lens and provides at the position indicated by reference 34 an image of the conventional exit pupil at 14; light from the image at 34 is visible at an enlarged pupil 26, spread in the plane of the drawing along a line, as indicated by the doube-headed arrows, and of width comparable with the diameter of the conventional exit pupil at 14.
An observer's eye 28 at any position along the line pupil 26 can receive a narrow pencil of rays, such as the pencil of rays 30, of length in the plane of the drawing determined by the aperture of the eye. The area of the 10 cylindrical surface on which this image is focused is referenced 32.
If the eye moves along the line pupil 26, different pencils of rays from different parts of the cylindrical surface and therefore from different parts of the image on that surface will be received, but at no eye position will it be possible to view the whole area of the image received by the cylindrical lens 22. A similar result is obtained if the eye is stationary and the lens 22 is moved parallel to the line pupil 2 6.
If a field lens having the property defined above is introduced between the position 34 and the observer's eye 28, and if the lens 22 is one of a multiplicity of cylindrical lenses on the surface of the disc 16, 20 then a view at any position along the line pupil 26 would be able to see a small part of the image focused on the surface of each cylindrical lens.
However, the pupil 26 is still enlarged only in the plane of the drawing so that, even with a multiplicity of cylindrical lenses, it is still essentially a line pupil If, however, two orthogonal sets of cylindrical lenses are provided, as shown in Figure 2, the pupil will be enlarged in two orthogonal directions and the overall enlarged pupil will be of rectangular form. ~his howe~ er, as previously explained, will still provide an incomplete field, bccause the area on each cylindrical lens from which an image is recei~ed by the eye is still less than the whole lens area.
If the discs 16, 18 in Figure 2 are rotated about the axis 20 in the same direction and at the same speed, the areas of image visible to the eye through elemental areas of the discs move continuously so that in a full rotation of the disc, substantially the ull field area is visible for some proportion of the scan. If the discs are rotated fast enough, persis-tence of vision results in an effectively full field of view being received at theenlarged pupil, which is now circular due to the rotation.
In Figure 2, both of the discs 16, 18 are transparent and an optical system containing two such discs will be referred to as a trans-mission system. It is also possible to have one disc transparent, the other having a reflective layer on either the grooved or the plane surface;
the optical systems incorporating such pairs of discs will then be of the reflection type as shown in Figure 4.
In Figure 4, light from a magnifying optical system 36 passes along an optical axis 38 through a transparent grooved disc 42 and is reflected by a second grooved disc 44 which is silvered on the front, grooved surface; the light passes again through disc 42 and a field lens system 48 to an observer 50. The discs can be rotated by an axle 46. The optical system is arranged so that a real image is focused on the plane of contact of the discs.
The observer 50 sees an enlarged image, which by persistence of vision provides a complete field view. The image can be viewed from a variety of head positions relative to the apparatus, because the exit pupil is enlarged - for example it can be of the order of s ~ inches in diameter.
Figure 5 shows a preferred embodiment of a microscope in accord-ance with the invention. Light from an object 52 passes through an objective lens system 54 to a projection eyepiece lens 56, is reflected by fixed plane mirror 58 to fixed plane mirror 60, and passes through a pair of rotatable grooved discs 62, 64 and a field lens system 66 to an observer 68. The system is arranged so that a real image of the object is focused on the plane of contact of the pair of discs 62, 64.
The discs 62, 64 are mounted on a rotatable cylindrical drum 70 carried by a rotatable hollow shaft 74 driven by a motor (not shown). The drum has a plurality of slots 72 in its surface to allow passage of light between the mirrors 58 and 60. The mirror 60 is supported by a fixed supporting stem 78 which passes through the rotatable hollow shaft 74.
The Figure 5 embodiment produces a single enlarged exit pupil which can cover both eyes. It is also possible to provide two enlarged exit pupils, at an average interpupilary spacing, by replacing the lenses 54 and 56, that is, apparatus below the line A-A in Figure 5, by a beam-splitter arrangement as shown in Figure 6. Light from the object 52 then passes through an objecti~-e lens system 80 to a conventional beam-splitter complex 82 which provides two partial beams 84, 86 reflected by respective plane mirrors 88, 90 to two eyepiece projection systems 92, 94. A beam from each system 92, 94 then passes into the remainder of the apparatus as shown in Figure 5, and through the discs 62, 64 to an o'bserver. The provision of two enlarged exit pupils can result in higher image brilliance without substantial loss of freedom of head movement.
It is also possible to provide a stereoscopic image at an enlarged pupil. In figure ~, light from an object 96 passes through conventional stereoscopic objective lens system 98 to a mirror complex 100 which provides correct right-and-left handedness in the final image. Light then passes through a pair of projection lens systems 102 which focus images of the object g6 on the plane of contact of a pair of transparent grooved discs 104, 106 and provides two enlarged exit pupils 108, 110 at average interpupilary spacing, after passage through a single field lens system 1~2.
A modification of the reflecting system shown in ~i,gure 4 is lQ"83S2 shown in Figure 8; the modification allows the production of an enlarged exit pupil of sufficient size to produce a biocular image. Identical parts are given identical reference numerals. Light from an object 114 passes through an objective lens system 116 and a projection lens system 118 to a plane mirror 120 which reflects light through a primary field lens system 122 to the two grooved discs 42, 44. Light is reflected by disc 44 back through the lens 122 and through a secondary field lens system 48 to the observer 50.
It is necessary to use the additional system 122 to increase the power of the field lens system so it can fulfil its normal requirements, i.e.
provide a full field of view in the absence of the grooved discs. Light is preferably incident as near as possible orthogonally to the disc surfaces to reduce distortion, and the geometrical constraints of this embodiment are such that the field lens 48 cannot be placed sufficiently close to the discs to be of short enough focal length to fulfil the field lens system requirements.Thus the additional lens system 122 is provided; its power is effectively doubled because light passes through it twice.
The apparatus in Figure 8 below the line B-B may be replaced by the arrangement shown in Figure 6, if two enlarged exit pupils are required.
In another modification, by replacing apparatus below the line by the items ~8, 100 and 102 of Figure 7, two stereoscopic enlarged pupils can be provided.
It is to be understood that application of the invention is not limited to microscopes; enlarged pupils can also be provided in other forms of optical instruments. Possible modifications to apparatus according to the invention include the provision of slightly curved discs instead of plane discs, which could be arranged to counteract field curvature effects.
Further, it is not essential that the focal plane coincides precisely with the plane of contact of the two grooved discs although this is always the preferred condition.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An optical system for viewing an object comprising optical means arranged to provide in a focal plane a magnified image of an object; a generally planar device arranged in said focal plane, there being on two generally parallel surfaces of the device respective arrays of grooves such that the cross section through each surface and transverse to the groove length is in the form of a plurality of arcs, the grooves in one surface being arranged transversely to the grooves in the other surface; means to rotate the device with said surfaces in or near to the focal plane; and a field lens system arranged between said planar device and the exit pupil to receive light from said device.

2. An optical system according to Claim 1, in which for each surface the grooves on the surface are parallel to each other.

3. An optical system according to Claim 1, in which the planar device comprises two plane discs each grooved on one surface.

4. An optical system according to any one of Claims 1, 2, or 3 in which the grooves are of such shape that each grooved surface comprises a plurality of alternate part-cylindrical depressions or protrusions.

5. An optical system according to any one of claims 1, 2 or 3 wherein the grooves are of such shape that each grooved surface comprises a plurality of alternate part-cylindrical depressions or protrusions and said section through each surface forms a sinusoidal curve.

6. An optical system according to any one of claims 1, 2 or 3 in which the device comprises two transparent circular discs in contact.

7. An optical system according to any one of claims 1, 2 or 3 in which the device comprises two circular discs in contact, one disc being transparent and the other disc having one reflecting surface.