Patent ID: 8730597

Claim:
A holding apparatus configured to hold an optical member, the holding apparatus comprising: a holding member configured to hold the optical member and including a contact surface that contacts with a projection portion of the optical member; and a structure supporting the holding member, wherein the contact surface inclines relative to a plane orthogonal to an optical axis of the optical member, wherein an inclination angle of the contact surface relative to the plane is set so that a relative position of an optical surface of the optical member to the structure is kept constant in a direction parallel to the optical axis when the optical member shrinks or expands, wherein the inclination angle is set based on at least one of a thermal expansion coefficient of the optical member, a shape of the optical member, a thermal expansion coefficient of the holding member, or a shape of the holding member, and wherein a following equation is satisfied: θ 1 =tan −1 {( L 13·α 3 −L 11·α 1 )/( R 1·( Ct 3 ·α 3 −Ct 1 ·α 1 ))}, where α 1 is the thermal expansion coefficient of the optical member, α 3 is the thermal expansion coefficient of the holding member, R 1 is a distance from the optical axis to a contact point, at the contact point the contact surface of the holding member contacting with the projection portion of the optical member, at a temperature in a direction orthogonal to the optical axis, L 11 is a distance from the contact point to the optical surface of the optical member at the temperature in the direction parallel to the optical axis, L 13 is a distance from the contact point a reference surface of the structure, the reference surface formed in a side near the optical member, at the temperature in the direction parallel to the optical axis, Ct 1 is a shape coefficient of the optical member, Ct 3 is a shape coefficient of the holding member, and θ 1 is the inclination angle.