| 摘要 |
PURPOSE:To attain a focus adjustment with high accuracy and high reliability without troubling manual operation by applying the detection of focus position at least twice by the sensor output so as to decide the focus. CONSTITUTION:A part of a projected light is sent to a focus detector 30 by a half mirror 9. The detector 30 is provided with a beam splitter, the incident light is divided into two kinds of optical lengths, a photodetector S1 is provided to a short optical length and a photodetector S2 is provided to a longer optical path. At the time of driving a step motor, the lens 7 is moved vertically by the action of an eccentric cam. The output signal of the detectors S1, S2 when the lens 7 is moved is a disturbed data having plural peaks due to noise. When maximum values K1, K2 of the output contrast have a maximum value due to noise, the obtained focus is deviated from the true focal position A by (l). By applying the focus detection at least twice, the resulting mean value is obtained, high accuracy is obtained and the reliability is improved to match the focus.
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