| 摘要 |
PURPOSE:To facilitate focusing by converting an optical image of a variable density picture to a picture signal and obtaining the difference between its maximum and minimum values and providing a display means whose display state is changed in accordance with this difference. CONSTITUTION:The picture on a microfilm 1 illuminated by a lamp 2 is projected not only to a screen 8 through a fixed mirror 6 and a half mirror 7 but also partially to a photoelectric transducer 15 which is placed to have the same optical path length as the screen 8. The photoelectric transducer 15 scans the image, and the maximum value and the minimum value of the picture read signal are detected by a maximum value peak holding circuit 18 and a minimum value peak holding circuit 19, and the difference is obtained by a difference circuit 20 and is converted to digital information by an A/D converter 21 and is decoded by a decoder 22 and is displayed on a display device 23. An LED array is used as the display device, and LEDs are lit successively toward the right according as the difference between the maximum value and the minimum value of the picture signal is increased.
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