Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1984-04-05
1985-10-15
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
250204, 250237R, 354406, G01J 120
Patent
active
045476632
ABSTRACT:
A focus detecting apparatus is disclosed which includes a focusing optical system for forming an object image on a predetermined focal plane and photoelectric devices disposed before and behind the focal plane at substantially equal distances from the plane. The photoelectric devices detect the focus states of the object images formed thereon respectively. The focus state of the object image on the focal plane is detected depending on whether or not the focus states on the photoelectric devices are equal to each other. According to the invention such a focus detecting apparatus further includes a mask for gradually decreasing the quantity of light incident upon the photoelectric devices in the direction away from the center of the incident beam. Under the action of such a mask, the focus states of object images before and behind the predetermined focal plane at substantially equal distances from the focal plane are made approximately equal to each other.
REFERENCES:
patent: 3975631 (1976-08-01), Takeda
patent: 4247763 (1981-01-01), Stauffer
patent: 4350443 (1982-09-01), Williamson
patent: 4352545 (1982-10-01), Uno et al.
Hosoe Kazuya
Kawabata Takashi
Kinoshita Takao
Kitagishi Nozomu
Sakai Shinji
Canon Kabushiki Kaisha
Nelms David C.
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