Catadioptric optical system and image pickup apparatus having the same

A catadioptric optical system comprising:

• a first imaging optical system that includes a catadioptric part configured to collect a light beam from an object to form an intermediate image of the object;
• and
• a second imaging optical system that includes a refractive part configured to image the intermediate image on an image plane,
• wherein the first imaging optical system includes a first optical element having a light transmission part around an optical axis and a reflection part including a surface as a reflection surface provided at an outer circumference side relative to the light transmission part and disposed at the object side, a second optical element having a light transmission part around the optical axis and a reflection part including a surface as a reflection surface provided at an outer circumference side relative to the light transmission part and disposed at the image side, and a negative lens in an optical path between the first optical element and the second optical element, the first optical element and the second optical element being disposed so that the reflection part of the first optical element and the reflection part of the second optical element face each other,
• wherein the light beam from the object emits to a side of the second imaging optical system via the light transmission part of the first optical element, the negative lens, the reflection part of the second optical element, the negative lens, the reflection part of the first optical element, the negative lens, and the light transmission part of the second optical element, in order, and
• wherein the following expressions are met:
• 0.1<|φn/φ1|<0.3
• 0.3<R1n/R2n<0.8
• where φn is a power of the negative lens, R1n and R2n are radii of curvature of lens surfaces of the negative lens at an object side and an image side, respectively, and φ1 is a power of the first imaging optical system.