| 摘要 |
<p>PURPOSE:To shorten exposure of a short second time, and also to obtain a fine- grained exposure step by switching forcibly the turning direction of a step- motor at an exposure time point corresponding to the brightness of an object to be photographed, and subdividing a part between the steps. CONSTITUTION:A photographed object brightness measuring circuit 1 compresses logarithmically a current signal proportional to the brightness detected by a photodetector 1a and outputs a brightness signal. Also, a step-motor driving pulse generating circuit 5 is constituted of a reference clock generator 5a, a pulse train generator 5b for generating a two phase pulse for driving a step- motor 51 by frequency-dividing a clock signal from said generator. In a process in which the motor 51 turns continuously in the forward direction and opens a sector, an exposure quantity controlling circuit 2 executes an apex operation of film sensitivity and photographed object brightness by a differential amplifier 2a, and when the time corresponding to a difference of both of them elapses, an inversion signal is outputted from a timer 2d. As a result, a step-motor driving circuit 6 is inverted, the motor 51 is rotated backward forcibly and closes an optical path, and an optimum exposure to the photographed object brightness is ended.</p> |
