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US 4,784,480 AGranted
Focusing-in-part lens system
AssigneeCanon Kabushiki Kaisha
InventorsHideo Yokota, Yasuyuki Yamada
Life of this patent
Estimating the term…
Abstract
An objective lens comprising a front lens group of positive power followed by a diaphragm, and a rear lens group of positive power axially movable for focusing and comprised of a plurality of members with the strongest diverging surface of concave curvature being arranged toward the front of the lens.
Claims4
A focusing-in-part lens system comprising:
- frontmost lens means having a positive refractive power and maintained stationary during changing of the object distance, a fixed diaphragm arranged on the image side of said frontmost lens means, and rear lens means arranged on the image side of said diaphragm, said rear lens means including an axially movable lens group for changing of the object distance consisting of a plurality of lenses and having a positive refractive power with the strongest diverging surface in this group with its concave curvature toward the front;
- said lens system satisfying the condition of
- 1.2<FA/F<2.2
- wherein F represents the focal length of the whole system, FA represents the focal length of the lens means closer to the object than said movable lens group of the rear lens means.
1 more element
Dependencies are inferred from the claim text.