Optical system for a focal point detecting device

Details Optical system for a focal point detecting device Optical system for a focal point detecting device

1988-11-17

1990-07-03

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

250204, G01J 120

Patent

active

049393570

ABSTRACT:
A condenser lens disposed behind a film equivalent plane, a pair of light splitting elements disposed behind the condenser lens, and a focal point detecting apparatus. The radius of curvature of a front surface of the condenser lens at the film equivalent plane side is larger than that of a rear surface of the condenser. A path length L from the film equivalent plane to the rear surface of the condenser lens is set in a range of 3.2 mm>L>3.6 mm on the assumption that the path length L is not substantially expanded by a refractive material. The pair of light splitting elements are disposed in symmetricy with respect to a meridian plane of the condenser lens. The focal point detecting apparatus is adapted to detect a focal point by finding a relative positional displacement of an objective image which is reimaged by the pair of light splitting elements. Due to the foregoing construction, in an optical system of a focal point detecting device of the present invention, even if a spherical lens, which is easy to manufacture, is used for a condenser lens, instead of an aspherical lens which is difficult to manufacture, the zone of focus can be made long enough so that the effect of dust on the condenser can be minimized. In addition, aberration distortion can be corrected thoroughly.

REFERENCES:
patent: 4580042 (1986-04-01), Tokutomi et al.
patent: 4716431 (1987-12-01), Shindo
patent: 4794416 (1988-12-01), Mukai et al.

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