US8325267B2 - Image Pickup Apparatus Comprising an Image Pickup Optical System Including an Optical Element Having Optical Incident and Optical Emergent Surfaces and a Fine Textured Structure Having a Mean Pitch Shorter Than a Wavelength of Visible Light, and an Image Pickup Unit Configured to Receive an Image Formed by the Image Pickup Optical System, and Meeting a Specified Diameter Condition | Patent Bear