| 摘要 |
A differential value of a characteristic curve of a focus distance of a zooming lens versus a position of a focus lens is calculated or found from a table in a contrast or phase difference type auto focus mechanism by detecting a high frequency part of an image signal. A follow-up speed of a focus lens is stepped or continuously changed based on the differential value. A focus position of a focus lens can therefore be changed smoothly corresponding to displacement of a focus distance of a zooming lens. A current brightness and a brightness when the evaluative value is peak is compared. If a brightness difference is large, a peak is not recognized and processing is repeated. Also, a gain of an amplifier is reduced corresponding to a linear-, step- or curve characteristic of a focus position of the focus lens versus a focus distance of the zooming lens when a gain of an AGC circuit is relatively high, so that noise is a high frequency part is reduced. If an iris of the apparatus is relatively closed a gain of the AGC or an amplifier is relatively high, noise increases and the reference value therefore increases to judge a peak of an evaluative value certainly. If the iris is relatively opened, a gain of the AGC and the amplifier is relatively low and noise decreases wherein a peak is rapidly detected without the focus lens passing a focus point.
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