| 摘要 |
PURPOSE:To make correction excellently by selecting the area and transmissivity of a transparent film within specific ranges. CONSTITUTION:A transparent film is formed on the 1st or the 2nd curved or plane surface counted from an object or image plane side to part of an effective diameter containing an optical axis, and at least 80% of the area S of the thin film part including the optical axis is formed having uniform transmissivity T; when the area of the effective diameter of the curved or plane surface is denoted as So, 0.4<T<=0.7 and 0.2<=S/So<=0.5 and a normal lens surface is formed outside the thin-film part. Consequently, corrections are made excellently. Further, the half field angle of a lens within a practical use range which needs to be improved is 20-35 deg., the center illuminance decreases too much within this range when T>0.7, and corrections cannot be made excellently. When T>0.7, the center illuminance does not decrease, so corrections can not be made excellently either. When S/So>0.5, a decrease in illuminance extends to the peripheral part and when S/So>0.2, only the center part is corrected and the intermediate part can not be corrected.
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