| 摘要 |
PURPOSE:To perform extremely accurate control by arranging an electromagnet where a half shift in the period from a magnet to a magnetic body is obtained, and powering down the electromagnet before a diaphragm position attains to a calculated aperture value. CONSTITUTION:The magnet 4 and electromagnet 5 are positioned relatively with a half shift in the array period of comb teeth of a pulse plate 2, and the magnet 4 and electromagnet 5 balance each other in attractive force. A magneto-resistance element 1 outputs a pseudo since wave voltage corresponding to the number of comb teeth passing over the element surface from an output circuit 35, and pulses are counted by a pulse conter 55; and a specific number of pulses generated by a pulse generator 58 are added, and the sum is inputted to comparators 56 and 60 while the counted value of a photometric arithmetic circuit 57 which corresponds to an aperture value is inputted to the comparator 60. When both values become equal to each other, the comparator 60 outputs a signal to power off the electromagnet 5, and the attraction balance between the magnet 4 and electromagnet 5 is lost to reduce the speed of the pulse plate 2. When the counted value of the digital comparator 56 becomes equal to the aperture value inputted from a circuit 57, an electromagnet 32 is powered off. |
