Patent ID: 7336421

Claim:
An optical system comprising: an aperture diaphragm; and plural light-transmitting members, including a plurality of lens elements, wherein: at least one said light-transmitting member has an optical surface which is non-convex with respect to said aperture diaphragm; an anti-reflection coating is provided on said optical surface; said anti-reflection coating has a plurality of layers, including an upper layer formed by a sol-gel method, and at least one layer formed by vacuum deposition and located between said upper layer and said optical surface; and the following formula is satisfied: 0 ≦f/rs< 10.0 wherein “f” is a focal length, and “rs” is a radius of curvature for the optical surface with said anti-reflection coating, “rs” having a positive value (rs>0) if the optical surface is concave with respect to said aperture diaphragm.