Patent
1988-11-21
1991-04-09
Henry, Jon W.
350469, G02B 934, G02B 2300, G02B 2324
Patent
active
050059602
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a relay lens system comprising two rod-type lens elements and two further optical elements in symmetrical arrangement relative to the center plane of the object plane and the image plane, as defined in the introductory clause of patent claim 1.
Such relay lens systems, which are also termed image transfer systems, are used specifically in endoscopes and also for other types of periscopes such as technoscopes, cystoscopes, or the like. For this reason, the term "endoscope" will be used in the following as a "generic term" without any restriction of the general applicability of the invention.
The use of rod-type lens elements has been proposed for the first time by Prof. Hopkins (GB Patent No. 954 629): according to Prof. Hopkins' fundamental idea, each relay lens system--i.e. any lens system which transfers the image produced by the endoscope objective to the following relay lens system or the eyepiece--is composed of two bi-convex rod-type lenses or at least two additional meniscus lenses. The combination of rod-type bi-convex lenses with meniscus lenses contributes, on the one hand, to a high image brightness, while it is suited, on the other hand, to compensate sufficiently the optical aberrations which are troublesome in relay lens systems, i.e. astigmatism and curvature of field, as has been recognized by Prof. Hopkins.
Based on Prof. Hopkins' works, a number of modified relay lens systems has been described in patent literature thereafter, wherein rod-type lens elements are employed as well. The published German patent application No. DE-AS 25 54 952, the German patent No. 26 19 393, the published German patent application No. DE-OS 35 34 210, and the published German patent application No. DE-OS 35 35 028 should be mentioned here only by way of example.
Compared against Prof. Hopkins' fundamental idea, the relay lens or image transfer systems described in the foregoing patent documents are of a relatively complex design, aiming at an improved compensation of the aberrations in imaging.
The published German patent application No. DE-AS 25 54 952 proposes, for instance, the use of bonded elements as relay lenses, with insertion of optical flats between the field lenses and the relay lenses. This arrangement not only increases the number of required optical elements but also renders the mechanical structure of the endoscope more expensive as all the optical elements are separated from each other by air gaps.
The German patent No. 26 19 393 describes the use of a total of four rod-type lenses, partly consisting of bonded elements, and a fluid lens in each relay lens system. More detailed comments upon the high costs of production of such a structure may be dispended with here.
The published German patent application No. DE-OS 35 34 210 describes as well the use of "thick" meniscus lenses in addition to the bi-convex rod-type lenses, wherein either the rod-type lenses or the thick meniscus lenses are designed as bonded elements.
According to the most recent idea proposed in the above-referenced documents, i.e. DE-OS No. 35 35 028, each relay lens group comprises even five lens elements part of which is additionally designed as bonded elements.
None of these more recent publications, however, mentions a reasonable relationship between the achieved improvements of both the imaging quality and the image brightness, and the increased production costs.
Moreover, quite a number of publications discuss measures to increase the cross-sectional area available for the path of rays and thus the image brightness with a given diameter of the endoscope or periscope, respectively. The common fundamental idea which can be taken from these publications consists in rendering spacers between all lenses superfluous in order to make the cross-sectional area occupied by the spacers available as well for the beam of rays.
The published German patent application No. DE-AS 23 05 473 therefore includes the idea of designing the relay lens system(s) of the en
REFERENCES:
patent: 4693568 (1987-09-01), Takahashi
Henry Jon W.
Med Inventio AG
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