| 摘要 |
PURPOSE:To eliminate the influence due to stain of an optical system, by detecting the light just before incidence to the surface of a photosensitive drum to compensate a reference voltage in an exposure control circuit where a clamp illuminance measured value is compared with the reference voltage to perform dimming. CONSTITUTION:An original on an original placing glass plate 2 is illuminated with an exposure lamp 1, and the reflected light is transmitted to a photosensitive drum 7 through optical systems 4, 5, and 6 to expose the image. The illuminance of the lamp 1 is measured by an optical sensor 8, and feedback to the lamp power source is performed in accordance with the difference between the measured value and the reference voltage, and the adjustment is performed by a dimming circuit 10A so that the illuminance is made constant. When optical systems 4, 5, and 6 are dirty, the light incident to the photosensitive drum 7 is weaker through the illuminance of the lamp is the reference value; and therefore, the intensity of the light is measured by an optical sensor 9, which is freely moved out from and into the optical path, just before the photosensitive drum 7, and said reference voltage is changed to increase the illuminance of the lamp in accordance with the stain. |
