| 摘要 |
PROBLEM TO BE SOLVED: To provide an image-formation optical system having a large viewing angle, achieving high definition and realizing miniaturization. SOLUTION: In this optical system, luminous flux from an object passes through an aperture, a 1st optical group and a 2nd optical group in order and forms an object image on the surface of an imaging device without forming an intermediate image, and the 1st optical group is equipped with at least one optical surface having positive power and one optical surface having negative power, and the 2nd optical group is equipped with a prism having at least one rotationally asymmetric reflection surface and having positive power. The optical system satisfies conditional expressions -0.1<=Xf/Di<=0.5 and 0.5<=(Xf+Xr)/Di<=1. Provided that a ray passing through the center of the aperture and leading to the center of the imaging device is set as an axial principal ray, and Xf means optical path length obtained until the axial principal ray leads to the optical surface having the positive power of the 1st optical group from the aperture, Xr means optical path length obtained until the axial principal ray leads to the optical surface having the negative power of the 1st optical group from the optical surface having the positive power of the 1st optical group and Di means optical path length obtained until the axial principal ray leads to the 2nd optical group from the aperture.
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