| 摘要 |
A disclosed projection optical system projects images on a surface to be projected on. The projection optical system includes a first optical system including at least one refraction optical system and having positive power as a whole, a folding mirror, and a second optical system including at least one reflection surface having power and having positive power as a whole. Further the folding mirror folds a light path from the first optical system to the second optical system, and in a plane including an optical axis of the first optical system and a normal line of the surface to be projected on, the following conditional expressions (1) through (3) are satisfied (1) 0.43@d1, (2) 0.43@d2, and (3) 0.7@d2/d1@2.0.
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