Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1986-02-14
1987-08-18
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
250204, 354402, G03B 310
Patent
active
046879153
ABSTRACT:
In automatic focusing devices of the type which detect a defocus degree and a focusing direction and according to the results of detection, automatically shift a lens to an in-focus position, an accurate defocus degree cannot be obtained when the lens position is far away from an in-focus point. In such a case, focus detection must be carried out by driving the lens in the focusing direction solely according to information on the focusing direction, which, because of a weak signal from the detection output necessitates a slow lens driving speed and accordingly takes a long time for shifting the lens position to an in-focus point. Another problem with conventional devices is the possibility of overshoot which happens while bringing the lens to the in-focus point by driving it to a defocus degree. Then, after such anovershoot, the lens is again driven to the defocus degree in the reverse direction. This results in a second hunting which tends to occur before the in-focus position is attained. An automatic focusing device according to the invention solves these problems by driving the lens in the focusing direction, detected when the lens is in a position away from an in-focus point and by inhibiting the detecting action while the lens is driven. Furthermore, when overshoot once happens, the detected defocus degree is decreased and the decreased defocus degree is transmitted to a lens drive circuit driving the lens to a decreased degree in the next lens driving process to preclude the possibility of hunting.
REFERENCES:
patent: 4091275 (1978-05-01), Wilwerding
patent: 4333007 (1982-06-01), Langlais et al.
patent: 4473743 (1984-09-01), Ishikawa
Kawabata Takashi
Sakai Shinji
Canon Kabushiki Kaisha
Westin Edward P.
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