| 摘要 |
PURPOSE:To correct position of a scanning head to scanning light spot on an original picture drum by detecting deviation from focused position of a pickup lens simply. CONSTITUTION:A light projecting lens 7 and a light receiving lens 8 are provided on both sides of a pickup lens 3 provided in the scanning head 2, and an image of a minute light spot 10 is formed on the film surface of the original picture 1 by a source of light spot 9. On the other hand, a light sensor 11 having sectional areas 11a, 11b is provided in the rear of the light receiving lens, and an image of above-mentioned light spot 10 is formed in somewhat blurred state. When the distance between the head 2 and original picture 1 is in focussed position of the lens 3, light detecting output from sectional areas 11a, 11b is the same and no output is made from a differential amplifier 16. However, if the focal point is deviated by change of thickness etc. of the original picture 1, difference is caused in output of sectional areas 11a, 11b, and accordingly, a correction signal is generated from the differential amplifier 16. When the correction signal is outputted, the head 2 is driven to focused position by a servo motor 6.
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