Patent ID: 8894219

Claim:
An optical projection system for enlarging an image formed on an image forming element to project the enlarged image on a projection surface, the optical projection system, comprising: a coaxial optical system including a plurality of lens groups that share an optical axis, and a mirror having power, the coaxial optical system and the mirror being arranged in this order in an optical path from the image forming element to the projection surface, wherein the plurality of the lens groups includes a plurality of focus groups configured to independently move in an optical axis direction for adjusting a focus, one of the focus groups is a first focus group having a negative refractive power, and among the rest of the focus groups, focus groups having a positive refractive power are configured to move in a direction identical to the first focus group and the optical axis direction, and focus groups having a negative refractive power are configured to move in a direction opposite to the first focus group and the optical axis direction.