| 摘要 |
PURPOSE:To obtain an image of high contrast and less false signal by constituting an optical low pass filter of first and second periodic structures and providing a part where a transfer function (MTF) lower than the cut-off space frequency is higher than a prescribed value in one or two or more directions and making the area, where the MTF higher than the cut-off space frequency is lower, twice or more as wide as the cut-off space frequency. CONSTITUTION:The optical low pass filter consists of at least first and second periodic structures 1 and 2. The part where the MTF lower than a cut-off space frequency fc is higher than a prescribed value, for example, the value indicated by a line (a) in the figure is provided, and the area where the MTF higher then the cut-off space frequency fc is lower, desirably, <=0.3 is made twice or more as wide as the cut-off space frequency fc. Thus, the image of high contrast and less false signal is obtained.
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