| 摘要 |
A retainer for holding a rotationally symmetrical optical element, includes a retaining member that holds the optical element via three support parts arranged at approximately 120° intervals, and a joint member that joints the optical element with the retaining member, wherein |(zb-0.6wb)-(zg+1.2)|<=1 is met, where zg is a coordinate of a gravity center of the optical element, zb is a coordinate of a center position of a width of said joint member in the z axis direction by which said joint member contacts the optical element, and wb is the width of said joint member in the z axis direction by which said joint member contacts the optical element.
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