| 摘要 |
PURPOSE:To make corrections excellently by approximating the transmissivity of a thin-film part to a value corresponding to illuminance at a maximum field angle. CONSTITUTION:A translucent thin film is formed on one surface side to part of an effective radius containing the optical axis and at least 80% of the thin film part containing the optical axis has uniform transmissivity T. In this case, 0.4<=T<=0.7 and a blank material outside the thin-film part or a filter of a parallel plane plate made of an antireflection film is arranged at the object plane side or image plane side of the optical axis of a lens system. Consequently, corrections are made excellently. Further, the half field angle of a lens within a practical use range which need to be improved is 20-35 deg. and center illuminance decreases too much when T<0.4, so that corrections are not made excellently. The center illuminance does not decrease when T>0.7, so corrections are not made excellently either.
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