| 摘要 |
PROBLEM TO BE SOLVED: To provide a projection lens of a coaxial system suitable to, specially, a projection type display device etc., such as a liquid crystal projector by using a diffraction optical element which has high diffraction efficiency in the whole use wavelength range (light in visible region) and can reduce incidence angle dependency of light incident on the diffraction optical element. SOLUTION: The projection lens of the coaxial system can be realized by introducing a stack type diffraction optical element at a position where the absolute value of the height from the optical axis of a pupil paraxial light beam passing through each lens is large and the center of a circle or ellipse forming the diffraction optical element is shifted from the optical axis of an introduced lens substrate according to a distribution of light beams incident on a surface of the diffraction optical element. COPYRIGHT: (C)2005,JPO&NCIPI
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