Patent ID: 8128238

Claim:
A projection optical system comprising: a projection surface configured such that an image conjugate to an object is projected; plural optical elements having a refractive power; and a deflecting element having no refractive power configured to deflect an optical path of a light beam and to pass the light beam having a deflected optical path between the plural optical elements; and wherein a normal line of the projection surface at a center of the projection surface does not pass through the plural optical elements or between the plural optical elements; wherein the plural optical elements comprise a first optical system having a positive refractive power and configured to form an intermediate image conjugate to the object and a second optical system comprising at least one optical element and configured to form an image conjugate to the intermediate image; wherein the deflecting element is provided in an optical path between the second optical system and the projection surface; wherein a light beam from the deflecting element to the projection surface traverses a light beam from the first optical system to the second optical system; and wherein the deflecting element is a detachable element.