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US 5,253,112 AGranted
Rear conversion lens
AssigneeNikon Corporation
InventorsKenzaburo Suzuki, Yoshinari Hamanishi
Life of this patent
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AssigneeNikon Corporation
InventorsKenzaburo Suzuki, Yoshinari Hamanishi
Estimating the term…
The rear conversion lens of the present invention is compact and maintains an excellent imaging performance even when it is mounted on a telephoto objective lens the enlargement magnification of whose focal length is relatively high, e.g. about double and whose F-number is of the order of 2-2.8, and moreover does not intercept a light beam even in the fully open state of the aperture. The rear conversion lens of the present invention is an RCL adapted to be mounted on the image side of an objective lens and having negative refractive power for enlarging the combined focal length of itself and the objective lens, and has, in succession from the objective lens side, a first lens unit of positive or negative refractive power, a second lens unit of negative refractive power and a third lens unit of positive refractive power, the first lens unit having a positive lens most adjacent to the object side, and when the air gap between the first lens unit and the second lens unit is D.sub.1 and the air gap between the second lens unit and the third lens unit is D.sub.2 and the on-axis lens thickness from the first surface to the last surface of the RCL is .SIGMA.d and the focal length of the entire RCL system is f.sub.R, the RCL satisfies the following conditions: 0.13<D.sub.1 /.SIGMA.d<0.25 0.005<.vertline.D.sub.2 /f.sub.R .vertline.<0.05
A rear conversion lens adapted to be mounted on the image side of an objective lens and having negative refractive power for enlarging the combined focal length of itself and said objective lens, said rear conversion lens including, in succession from said objective lens side, a first lens unit having a positive lens component most adjacent to the object side and having positive or negative refractive power as a whole, a second lens unit having negative refractive power, and a third lens unit having positive refractive power, said rear conversion lens, when the air gap between said first lens unit and said second lens unit is D.sub.1 and the air gap between said second lens unit and said third lens unit is D.sub.2, being designed to satisfy the following conditions:
Dependencies are inferred from the claim text.