Focus detecting optical system and camera provided with the same

A camera comprising:

• a focus detecting optical system;
• a finder optical system;
• a photographic lens;
• path splitting means splitting an optical path from the photographic lens to direct the optical path toward an image sensor or a film and toward the finder optical system;
• and
• a reflecting means conducting the optical path of the photographic lens to the focus detecting optical system,
• the focus detecting optical system detecting a focus position of a photographing optical system from a positional relationship between at least one pair of secondary object images, wherein the focus detecting optical system comprises:
• a condenser lens placed in the proximity of a preset imaging plane equivalent to an imaging plane of a photographic lens;
• a pair of aperture stops dividing a pupil of the photographic lens placed on an exit side of the condenser lens into two areas;
• and
• a pair of re-imaging lenses for forming two secondary object images corresponding to the aperture stops, and satisfies the following conditions:
• 0.45<|mg|<0.750.75<|R1/R2|<1.25R3/R4|≦0.02
• where mg is an imaging magnification of the focus detecting optical system, R1 is a radius of curvature of an entrance surface of the condenser lens, R2 is a radius of curvature of an exit surface of the condenser lens, R3 is a radius of curvature of an entrance surface of each of the re-imaging lenses, and R4 is a radius of curvature of an exit surface of each of the re-imaging lenses.

A camera comprising:

• an image sensor provided with a light-receiving surface receiving light from a photographing optical system;
• and
• a focus detecting optical system detecting a focus position of the photographing optical system from a positional relationship between at least one pair of secondary image objects with light from the photographing optical system,
• wherein a diameter of an image circle of the camera is substantially a half of the diameter of the image circle of a 135 format camera.