Patent ID: 6995918

Claim:
A projection optical system for projecting an image of an object onto an image plane, said projection optical system comprising: a first imaging optical system for forming an image of the object, said first imaging optical system including a first mirror for reflecting and collecting abaxial light from the object; a second imaging optical system for re-imaging the image upon the image plane; a second mirror for reflecting the abaxial light from said first mirror to the image plane side, whereby the abaxial light is caused to pass outside of an effective diameter of said first mirror; and a field optical system including three lenses each having a positive refractive power, wherein the abaxial light passed through the outside of the effective diameter of said first mirror is refracted by said three lenses toward a direction nearing an optical axis of said three lenses, wherein, in a meridional plane, the abaxial light passes through only one side of said three lenses with respect to the optical axis, wherein light that has passed through said three lenses is directed to said second imaging optical system, and wherein said first and second imaging optical systems are disposed along a common optical axis.