| 摘要 |
PURPOSE:To reduce the cost by simplifying the circuit by performing the analog arithmetic of a measured value and an exposure determination factor to be combined with it which are both obtained as analog values and then by converting the output of the analog arithmetic into a digital value. CONSTITUTION:The value of subject's brightness measured by photodiode PD is digitized by AD converter 32 and set in comparator 33 as a reference digital value. Then, when a pulse signal value generated through the rotation of pulse motor 19 becomes equal to the reference digital value or reaches a constant ratio, the current supply to magnet 29 is stopped and lock lever 25 engages with an sperture lock gear to stop the rotation. Then, gear train 21 linking to gear 28, sector-formed gear 18, aperture driving lever 15, and aperture lever 23 also stops and the diaphragm in photographic lens 22 is held constant. Therefore, the number of pulses that pulse motor 19 generates and the extent of aperture operation of diaphragm lever 23 are preset, so that control over a photographic diaphragm value can be exercised. |
