| 摘要 |
PURPOSE:To eliminate a deviation from the best image plane of each color and to prevent the image forming performance of a color separation optical system from deteriorating by varying the thickness of a color separation filter according to wavelength ranges of the respective colors. CONSTITUTION:The distance between a document surface 1 and a lens 2 is S and the distance between the lens and a photosensitive body or image pickup element 4 is S'; and conjugation distance which is the distance between the document and element 4 is L and the distance between a Gaussian image point and the best image plane is D. The color separation filter 3 is increased or decreased in thickness according to focal length, image forming power, and wavelength ranges alpha, beta, gamma, and delta of the respective colors. Simultaneously, the distance S is also varied according to the thickness. Consequently, the conjugation length L of each color coincident with the power and further the best image plane D of each color has no deviation, so the image plane matches with the element surface 4 and the image forming performance of the color separation optical system is prevented from deteriorating.
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