| 摘要 |
PROBLEM TO BE SOLVED: To reduce returned light (back reflection) of transmission light and to reduce the stray light of an optical system by providing a light absorbing member absorbing light at the central part of the reflection surface of a secondary mirror. SOLUTION: A black mask 12 is provided coaxially at the central part of a convex surface 11a being the reflection surface of a secondary mirror 11 and partially absorbs light L' passing through a group of collimator lenses. The shape of the mask 12 is a mountain type obtained by turning a parabola around a symmetry axis. That is, in this optical antenna, because the mask 12 is provided coaxially at the central part of the convex surface 11a being the reflection surface of the mirror 11, it has a function absorbing a part of the light L' passing through the group of collimator lenses in a very small area in the neighborhood of the center of the mirror 11. Then, it is possible to suppress returned light quantity by reducing reflectance in the surface 11a of the mirror 11 patially. Consequently, returned light (back reflection) is reduced and stray light of an optical system is reduced. |
