| 摘要 |
PURPOSE:To maintain the mean input electric power at a certain value even if duty ratios are different between a period of a first light intensity and a period of a second light intensity, by controlling the mean electric power inputted to the light source during these periods at a predetermined value. CONSTITUTION:A data of an appropriate amount of exposure light set in a digital switch 22 is read by a CPU30. The CPU30 supplies a target value data D2 to a comparator 62. The CPU30 emits a data D0 to a D/A converter 49 where it is D/A converted to increase the electric power supplied to a mercury discharge lamp 1. The CPU30 also emits a clear signal SL so as to open a shutter 3 by driving it with 25. A counter 61 of a photometry circuit 21 is cleared by outputting the signal CL. A light receiving signal Si from an element 9 is converted by 60 to a pulse signal S2 which is counted by 61. When D1=D2, a stop signal SP is sent to the CPU30 so as to close the shutter 3 by driving it with 25, while the content of D0 of the CPU is returned to the rated input power from the increased power. According to this constitution, the light intensity of a lamp can be held at a certain level and the lamp is prevented from being excessively inputted, and from being deteriorated in its life and from breakage. |
