Optical: systems and elements – Compound lens system – Microscope
Reexamination Certificate
2000-04-21
2001-04-10
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Compound lens system
Microscope
C359S368000
Reexamination Certificate
active
06215589
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an optical system for a stereoscopic surgical microscope for interchanging two parallel light rays with simultaneous image reversion for both rays without parallel offset of the emerging pair of rays with respect to the entering pair of rays, comprising elements reflecting on one side and two elements reflecting in parallel on both sides, all arranged in a plane perpendicular to the incident rays, each of the elements reflecting on both sides reflecting with its front side the incident ray via the elements reflecting on one side to the rear side of the respectively other elements reflecting on both sides.
Prism systems for stereoscopic image erection of this type are known (DE-C 38 26 069). From the viewpoint of application technology, it is desirable to accommodate the optical arrangement in the microscope in a way which saves as much space as possible. To avoid undesired light losses, it is endeavoured to obtain shortest possible optical path lengths within the device. Since surgical microscopes are generally mounted movably to allow them to be oriented freely, but nevertheless have to be fastened stably, the weight of the microscope must be kept down as much as possible.
SUMMARY OF THE INVENTION
The invention is based on the object of providing an optical system for stereoscopic image erection of the type stated at the beginning which makes possible an arrangement which is as space-saving and lightweight as possible for accommodating in a microscope and which keeps the optical path as short as possible.
Accordingly, all the optical elements are configured as flat, lightweight mirrors, comprising a flat, lightweight substrate with a metallic mirror coating of the surface on one or both sides, so that their substrate lies completely outside the optical path. Although the replacement of reflecting prisms by mirrors is known in principle in optics and is also mentioned in passing in the prior art (DE 38 26 069 C2, column 7, lines
52
-
55
), it is not evident how a reduction in the dimensions could be achieved by such a replacement.
On the other hand, the invention teaches a specific shaping of the elements mirror-coated on both sides which, together with the flat form of the mirrors mirror-coated on one side, makes possible a particularly compact arrangement of the optical system. The said shaping is in relation to a plan view along the optical axis (hereafter referred to as “plan view” for short). The optical axis of the mirror system refers in principle to the parallel longitudinal axis of the microscope central to the incident light rays. The incident light is formed by two extended bundles of light rays, which in the plane of the optical arrangement have a diameter of OD; referred to as light rays are the mid rays of the bundles of light.
In the plan view of the mirror system, the edge of the mirrors mirror-coated on both sides is, according to the invention, shaped in the vicinity of the optically neighbouring mirrors mirror-coated on one side such that it is tangentially virtually parallel to the reflecting surface of the latter. The mirrors mirror-coated on both sides are expediently cut such that they are oval, so that their edge is circular in plan view, with a diameter at least equal to OD; the tangent to the edge of the circle at the point of least distance from the optically neighbouring mirror mirror-coated on one side is then in any event parallel to the reflecting surface of the latter. The inventive shaping of the mirrors mirror-coated on both sides allows the mirrors mirror-coated on one side to be brought very close up to the mirrors mirror-coated on both sides, in principle until they touch.
On the other hand, the specific form of reflecting prisms, governed by the position of the substrate in the path of rays, excludes a shaping of the elements reflecting on both sides in the way according to the invention.
The replacement of reflecting prisms by flat mirrors in the present case is accompanied by considerable difficulties, due to the finite thickness SD of the mirror substrate of the elements mirror-coated on both sides. In the arrangement described by the prior art, this leads to a parallel offset of the emerging pair of rays with respect to the entering pair of rays of 1.41 SD; this offset is undesired, since it must be possible in practice to remove the optical system from the path of rays without the rays being offset.
The invention teaches that a correction of the disturbing parallel offset described can be achieved by an altered inclination, in comparison with the prior art, just of the mirrors mirror-coated on both sides, while retaining the orientation of the mirrors mirror-coated on one side. The difficulty here lies in the fact that, by altering the inclination of one of the mirrors mirror-coated on both sides, both emerging rays are always influenced at the same time; in this case, the emerging rays are not only offset with respect to the entering rays in the way intended but are also inclined in a disturbing way. It is therefore surprising that, by altering only two variables, namely the setting angle &lgr;, &lgr;′ of the mirrors mirror-coated on both sides with respect to the plane of the optical axis, four independent variables, namely the inclination and offset of the two emerging partial rays, can be corrected; a person skilled in the art assumes that this is possible only by altering two additional independent variables, for instance by altering the orientation of the mirrors mirror-coated on one side. However, it has surprisingly been found that this is not the case. By suitable choice of a setting angle &lgr;=&lgr;′, which must be greater than the angle disclosed by the prior art of &lgr;=45°, the parallel offset of the emerging pair of rays with respect to the entering pair of rays can finally be corrected. The specific choice of the angle &lgr;>45° depends inter alia on the substrate thickness SD of the mirrors mirror-coated on both sides.
The shaping according to the invention of the mirrors mirror-coated on both sides allows the reflection surfaces of the elements reflecting on one side to be brought up to the mid rays of the incident bundles of light to within the absolute minimum distance of 0.5 OD; OD here describes the diameter of the incident bundles of light in the plane of the optical arrangement. The prism system configured in the prior art, on the other hand, must have a distance of the reflecting surfaces of the elements reflecting on one side from the centre axes of the entering bundles of rays that is increased by least 40% in comparison with the inventive mirror system, of 0.705 OD. With the inventive mirror system, a maximum radial extent of the entire construction of R=1.205 OD+0.705 SD is achieved. Since in practice the mirror thickness SD can be kept small in comparison with the diameter OD of the bundles of light, the inventive arrangement comes close to a maximum radius of R=1.205 OD. This means a reduction in comparison with the prior art of almost 20% (DE-38 26 069 A1,
FIG. 3
; R=1.5 OD). In a corresponding way, the optical path of 2.82 OD of a ray of light in the plane of the optical arrangement can be reduced by 40% in comparison with the prior art (4 OD). On the other hand, the overall height is increased only minimally by the slight additional inclination of the mirrors mirror-coated on both sides, which is likewise accompanied only by a minimum increase in the optical path.
Configuring all the optical elements as mirrors and arranging them in such a way that their substrate lies completely outside the path of rays also has the advantage that the mirror substrate does not have to meet any requirements regarding its optical quality. Moreover, imaging errors inextricably linked with the passage of the light rays through the surface of the prisms are avoided.
It regularly happens in practice that a surgical microscope is to be used without interchanging of the two light rays and without image reversion. F
Alix Yale & Ristas, LLP
Moller-Wedel GmbH
Robinson Mark A.
Spyrou Cassandra
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