| 摘要 |
A focussing condition detector effects a photoelectric conversion of a focussing condition on the imaging plane of a focussing lens. An output from the conversion is subject to an arithmetic operation which derives an evaluation value according to a given formula. The evaluation value is compared against a decision level in order to produce a decision output which indicates whether the focussing condition achieved by the focussing lens is in an in-focus or an out-of-focus condition. A decision level is offset from a threshold value between two regions each representing the in-focus and the out-of-focus condition, respectively, in both directions. When an evaluation value moves from the region representing the in-focus condition into the other region representing the out-of-focus condition, one of the decision levels which is offset in one direction from the threshold value is used. When the evaluation value moves in the opposite direction, the other decision level is used.By thus incorporating hysteresis in the decision level used in the comparison process, a small, but rapid change in the decision output is prevented even in the presence of extraneous fluctuations.
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