Relay finder optical system of an single-lens reflex camera
View Patent ↗A relay finder optical system, of a single-lens reflex camera, includes a condenser lens group, a prism, and a relay lens group, in this order from a primary imaging plane. An image, which is formed on the primary imaging plane, and is upside down and inverted from left to right, is re-formed on a secondary imaging plane for viewing by a photographer. The relay lens group includes a positive front lens group, a negative intermediate lens group, and a positive rear lens group, in this order from the object. The most photographers-eye side lens element of the positive rear lens group comprises a positive lens element having a convex surface facing toward the image, and satisfies the following conditions: 1<SF (1) −6< f/fM <−3 (2) SF: the shaping factor of the most photographers-eye side positive lens element (SF=(r 1+ r 2 )/(r 1− r 2 )); r 1 : the radius of curvature of the object-side surface of the most photographers-eye side positive lens element; r 2 : the radius of curvature of the photographers eye-side surface of the most photographers-eye side positive lens element; f: the focal length of the relay finder optical system; and fM: the focal 25 length of the negative intermediate lens group.
1. A relay finder optical system, of a single-lens reflex camera, comprises a condenser lens group, a prism, and a relay lens group, in this order from a primary imaging plane which is optically equivalent to an imaging plane of the single-lens reflex camera,
wherein an image, which is formed on said primary imaging plane, and which is upside down and inverted from left to right, is re-formed on a secondary imaging plane for viewing by a photographer;
wherein said relay lens group comprises a positive front lens group, a negative intermediate lens group, and a positive rear lens group, in this order from an object; and
wherein the most photographer's-eye side lens element of said positive rear lens group comprises a positive lens element having a convex surface facing toward the eyes of a photographer, and satisfies the following conditions:
1<SF
−6< f/fM <−3
wherein
SF designates the shaping factor of the most photographer's-eye side positive lens element of said positive rear lens group (SF=(r 1 +r 2 )/(r 1 −r 2 ));
r 1 designates the radius of curvature of the object-side surface of the most photographer's-eye side positive lens element of said positive rear lens group;
r 2 designates the radius of curvature of the photographer's eye-side surface of the most photographer's-eye side positive lens element of said positive rear lens group;
f designates the focal length of said relay finder optical system; and
fM designates the focal length of said negative intermediate lens group.
2. The relay finder optical system of a single-lens reflex camera according to claim 1 , wherein said positive rear lens group comprises three separate positive lens elements.
3. The relay finder optical system of a single-lens reflex camera according to claim 1 , wherein said negative intermediate lens group comprises a negative biconcave single lens element.
4. The relay finder optical system of a single-lens reflex camera according to claim 1 , wherein said positive front lens group comprises a positive single lens element.
5. The relay finder optical system of a single-lens reflex camera according to claim 1 , further satisfying the following condition:
−0.35<m<−0.25
wherein m designates the lateral magnification of said relay finder optical system.