| 摘要 |
PURPOSE:To prevent unnecessary copying effectively by performing the averaged light measuring of the quantity of light transmitted through a microfilm, and then stopping automatic exposure adjusting operation which uses a minimum detecting circuit when the background part of an image is below a prescribed rate. CONSTITUTION:A control circuit 36 discriminates the rate of the background area of an original firstly by using the detection output of a discriminating sensor 35 for background area. This sensor 35 inputs a peripheral out-of-focus light image by a lens 24 because it is arranged closely to a half-mirror 25 and when its photodetection area is relatively large, the averaged light measuring of the light image passed through an aperture card 19 is carried out. A microfilm where a document, etc., is recorded has a >=90% black part as a background, and a film of a print pattern or photograph has a <=90% black part. For this purpose, the detection output of said sensor 35 is compared with a reference voltage to discriminate the rate of the background part and when the rate is decided to be <=90%, an automatic copying stop lamp 37A is turned on, stopping copying operation automatically. |
