Optical system and imaging device

An optical system comprising:

• a main mirror having a shape of a portion of a convex paraboloid which includes an opening in a center and is rotationally symmetric;
• a second-reflection mirror which further reflects light'reflected by said main mirror, said second-reflection mirror having a shape of a portion of a concave paraboloid which is rotationally symmetric;
• at least one lens which forms an image of the light reflected by said second-reflection mirror;
• a lens barrel holding said at least one lens;
• and
• at least one sub mirror each having a shape of a convex paraboloid which is rotationally symmetric,
• wherein a position of a front principal point of said at least one lens coincides with a focal position of said second-reflection mirror,
• an optical axis of said at least one lens is tilted with respect to a rotational axis of each of the convex paraboloid and the concave paraboloid, and
• said at least one sub mirror is positioned such that the light reflected by said at least one sub mirror is further reflected by said second-reflection mirror and is formed into an image through said at least one lens.