Structure for mounting an optical element

A structure for mounting on a base plate an optical element having a cylindrical portion and an optical axis, comprising:

• a holder member, having a flat bottom surface and an opening, formed by a cylindrical inner surface, through which the cylindrical portion of the optical element penetrates, said holder member rotatably holding the cylindrical portion of the optical element;
• and
• a support member, adjustably securable to said holder member, having an inclined upper surface and a bottom surface, the flat bottom surface of said holder member contacting the inclined upper surface of said support member in a face-to-face manner, said support member capable of being secured to the base plate, the optical element being mounted on the base plate at an optimum position by aligning the optical axis of the optical element in a predetermined direction while adjusting the position of said support member under said freely rotatable holder member until the inclined upper surface of said support member is in face-to-face contact with the flat bottom surface of said holder member and the bottom surface of said support member is in face-to-face contact with the base plate, and then securing said support member to said holder member and the base plate, substantially all of the cylindrical inner surface of said holder member remaining in contact with the cylindrical portion of the optical element while adjusting the position of said support member.