| 摘要 |
PURPOSE:To sufficiently exhibit the effect of a low-pass filter not only to an axial luminous flux but off-axis luminous flux as well by varying the arrangement pitch of a composite prism so as to meet the size of the pass section at which the luminous flux passes the composite prism. CONSTITUTION:The optical low-pass filter 13 is disposed in the position shown by a broken line A. The off-axis luminous flux 2 which is fine in the part apart by a specified distance from the optical axis in addition to the axial luminous flux 1 near the optical axis pass this filter 13. The filter 13 is, thereupon, formed with the plural large prisms near the center where the axial luminous flux passes to roughen the prism pitch and is formed with the plural small prisms 8 in the part near the end where the off-axis luminous flux 2 passes to fine the prism pitch. Namely, the pass section of the axial luminous flux 1 passing near the center of the filter 13 is large and therefore, the sufficient low-pass effect can be exhibited even if the pitch of the composite prism 15 is coarse, but the pass section is small in the part where the off-axis luminous flux 2 passes and, therefore the pitch of the prism 15 is fined in such a manner that at least one boundary line or vertex of the composite prism 15 enters the pass section of the off-axis luminous flux 2.
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