Patent ID: 8254039

Claim:
A variable magnification optical system comprising: a reflective optical element having a positive magnification power and configured to be movable relative to an object plane; and a refractive optical system configured to form an intermediate image between the object plane and the reflective optical element, the refractive optical system including plural refractive optical elements, wherein a substantially constant magnification of the intermediate image to the object plane is maintained before and after the magnification change applied to an image projected onto a screen by moving at least one of the plural refractive optical elements: increasing a distance between the screen and the reflective optical element increases a magnification applied to the image projected onto the screen, and a change in distance between the screen and the reflective optical element, to effect a change in magnification applied to an image projected onto the screen, is substantially the same as a corresponding change in distance between the reflective optical element and the object plane.