Lens system having selectively shiftable focal length

Details Lens system having selectively shiftable focal length Lens system having selectively shiftable focal length

1976-06-03

1980-12-23

Clark, Conrad J.

350184, G02B 1504, G02B 1518

Patent

active

042406978

ABSTRACT:
A zoom lens system is constructed of a focusing member, variator, compensator and an image-forming lens arranged on a common optical axis in this order with respect to incident light to function as a master lens. The image-forming lens is divided into an intrinsic exchangeable front part and a fixed rear part so that when the front part is substituted by an attachment lens. The range of variation of the equivalent focal length of the master lens can be shifted toward longer focal lengths without causing any change in the back focal distance as it is so required because of the fixed rear part of the image-forming lens with the constant back of photographic lens. The attachment lens is constructed from at least two lens groups axially spaced from each other, each of which is provided with a rearwardly concave negative meniscus-shaped air space to prevent the reduction of high grade imagery of the master lens which would be otherwise resulted by the above-identified substitution.

REFERENCES:
patent: 3512872 (1970-05-01), Lynch et al.
patent: 3751136 (1973-08-01), Kirchhoff
patent: 4015895 (1977-04-01), Hirose

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