| 摘要 |
A fly eye lens has cells in an optical functional portion, and first, second, and third positioning portions on an outer edge. The first and second positioning portions are located in a region of a plane normal to the optical axis of the lens, divided by a first reference line extending through a center of thermal expansion and located in the plane. The first and second positioning portions have side surfaces located on the first reference line. The third positioning portion has a side surface located on a second reference line intersecting the first reference line, extending through the center of thermal expansion, and located in the plane. Even when the fly eye lens thermally expands, the position of the center of thermal expansion does not change in an optical system, and desired optical performance can be continuously achieved.
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