Patent ID: 8717684

Claim:
An image pickup optical system, comprising: an aperture stop; and a negative meniscus lens located on an object side of the aperture stop so that a concave surface of the meniscus lens faces to an image side, wherein: the concave surface of the meniscus lens is an aspherical surface; an anti-reflection structure formed only on the aspherical surface, the anti-reflection structure including multiple structural parts made of an inorganic material and finer than a used wavelength; and the aspherical surface has a point that satisfies the following expression: |(1 /Rm− 1/ Rs )/ Rm|> 5.0×10 −5 (mm −2 ), where Rm denotes a radius of curvature in a meridional direction corresponding to a radial direction of the aspherical lens at the point, and Rs denotes a radius of curvature in a sagittal direction corresponding to a concentric direction of the aspherical lens at the point.