Automatic focusing device using a light sensor of center-split t

Details Automatic focusing device using a light sensor of center-split t Automatic focusing device using a light sensor of center-split t

1987-10-14

1989-08-15

Westin, Edward P.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

250204, 354403, 358227, G02B 704, G03B 310

Patent

active

048577170

ABSTRACT:
An automatic focusing device for use in a video camera comprises a first and a second light-receiving element, a first and a second integration circuit integrating output signals of the first and second light-receiving elements respectively and each having a function of proportional current integration and a function of fixed current integration, a first and a second comparator comparing integration output voltages of the first and second integration circuits with the same threshold voltage respectively, a microcomputer producing a focusing signal by detecting the period of time from a time when one of the integration output voltages of the first and second integration circuits reaches the level of the threshold voltage to a time when the other integration output voltage reaches the level of the threshold voltage, and a detection circuit detecting that one of the integration output voltages of the first and second integration circuits reaches the level of the threshold voltage on the basis of the comparator output signals, thereby changing over the operation mode of the integration circuits from the proportional current integration mode to the fixed current integration mode.

REFERENCES:
patent: 4755662 (1988-07-01), Fujiwra et al.

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