| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to obtain an excellent image with less reduction in diffractive efficiency even in off-axis, by making the distance from a point on an optical axis of a diffractive optical surface of a pupil center satisfy a specified condition. SOLUTION: In the optical system having a diffreactive optical element, the diffractive optical surface is formed on a spherical surface of radius of curvature r1, and the distance (t) from the point on the optical axis of the diffractive optical surface to the pupil P center satisfy the relation: 0.8<=r1/t<=1.2. At this time, the matter that the radius of curvature r1 of the spherical surface forming the diffractive optical surface coincides nearly with the pupil P center is preferred. Further, the matter that the diffractive optical surface is provided with plural ring zone-surfaces around the optical axis, and boundary surfaces of respective ring zone-surfaces are vertical to the spherical surface is preferred. Further, the matter that the diffractive optical surface is a binary optical surface having a stepwise section is preferred. In such an optical system, since main light is made incident from a direction nearly vertical to the diffractive optical surface, the diffractive efficiency isn't deteriorated, and the excellent image with less flare is obtained. |
