| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-performance inexpensive image-formation optical system which is miniaturized and thinned by folding an optical path by using a reflection surface having power. SOLUTION: In the optical system provided with plural reflection surfaces having the power; the reflection surface 12 having negative power is arranged closest to an object side and the reflection surface 22 having positive power is arranged closer to an image side than the surface 12 out of the reflection surfaces by setting order that a light beam from the object crosses as the order of the reflection surfaces. The optical system is provided with at least one reflection surface 13 between the reflection surface 12 having the negative power and the reflection surface 22 having the positive power, and an axial principal ray 1 made incident on at least one reflection surface 13 satisfies 45 deg.<|θ|.θis an angle formed by the ray 1 with a normal in the eccentric direction of the reflection surface at a point where the ray 1 crosses with at least one reflection surface 13.
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