| 摘要 |
PROBLEM TO BE SOLVED: To surely prevent needless light from being made incident on a projection optical system by sticking a polyhedral member having a larger refractive index than that of a prism to the outer surface part of the side wall of the prism. SOLUTION: A needless light discharging member 5 for discharging needless light is stuck to the outer surface part of the side wall 22b of the prism 22. The member 5 is formed of material having the larger refractive index than the prism 22 and stuck so that its base 5a may be brought into contact with the outer surface of the side wall 22b, and formed of a pyramidal member where a surface 5c is set as a base. Since the refractive index of the member 5 is larger than that of the prism 22, the needless light reaching the side wall 22b is made incident on the member 5 from the base 5a without being totally reflected on a boundary surface. The secondary reflected light made incident on the base 5a is totally reflected by the member 5 and the reflected light is transmitted from an upper surface 5b or a side surface 5c as it is and discharged to the outside.
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