US Patent 7605860 Image pickup optical system

Provided is an image pickup optical system capable of performing focusing in a wide region without a large increase in tilt angle in the case where an image of an object is picked up from a low angle. The image pickup optical system includes a first optical system and a second optical system, for enlarging an image formed by the first optical system and forming the enlarged image. A principal plane of the first optical system is tilted relative to an image plane of the second optical system.