| 摘要 |
A copying machine has an optical mechanism which varies a back focal length of a lens. A control circuit generates a control signal so that the optical mechanism changes the back focusing length of the lens so the lens is first focused on an upper surface of a microfilm and then on a lower surface of the microfilm. An optical sensor generates separate light quantity signals for each focusing position of the lens and these signals are held and compared in a circuit which then determines which surface of the microfilm bears a picture. The optical mechanism then appropriately adjusts the back focal length of lens.
|
