| 摘要 |
PURPOSE:To prevent the nonuniformity of exposure due to a variable power ratio from being generated by correcting the distribution of an emitted light quantity, by providing a storage means which stores a correction value to uniformize illuminance distribution on an image forming plane, and controlling a supplying power quantity to plural electrodes based on a stored content. CONSTITUTION:In a case where luminance due to the reflection of the emitted light of a discharge tube 1 on an original plane is uniform, illuminance in the neighborhood of a screen, especially the illuminance of an end part in a longitudinal direction is lowered. Therefore, either an input power value to respective coil shaped electrode 2 of the discharge tube or its duty factor, or the combination of both values is controlled by a control means 5 according to an inputted correction value stored in a memory 10, and thereby, the lowering of the illuminance of both end parts in the longitudinal direction is prevented from occurring. Also, the magnification of an original image is changed, and a several kinds of stored contents is stored in the memory so that the inputted correction value fitted to the magnification of an optical system can be called out when the angle of the image is changed, then, the illuminance distribution is corrected to almost uniform one corresponding to the change of the magnification.
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