Extrinsic light eliminator for autofocusing circuit

Details Extrinsic light eliminator for autofocusing circuit Extrinsic light eliminator for autofocusing circuit

1992-10-06

1994-02-08

Perkey, W. B.

Radiant energy

Ionic separation or analysis

Static field-type ion path-bending selecting means

2502014, G03B 1336

Patent

active

052852334

ABSTRACT:
An autofocusing circuit includes an extrinsic light eliminator including a light emitter such as an infrared emitting diode for projecting a signal light reflected by an object to be photographed and detected by a photodetector to determine the distance to the object. A chopper integrating circuit to convert the photocurrent from the detector to a corresponding voltage and simultaneously amplifies this voltage. In a preferred embodiment, the operating period of the chopper integrating circuit is set to 0.025 sec. multiplied by an integer in order to assure that any extrinsic light components derived from a commercial power supply is reliably eliminated from the detected photocurrent no matter whether the commercial power supply is of 50 Hz or 60 Hz.

REFERENCES:
patent: 4678323 (1987-07-01), Sato et al.
patent: 5189461 (1993-02-01), Ishiguro
U.S. Patent application Ser. No. 07/834,636, filed Feb. 12, 1992, entitled Range Finder for Passive Type Autofocussing Device.

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