| 摘要 |
A lens 10 is used in a state where a direction of an optical axis 1b passing through a curvature center of a lens surface is different from a direction of a gravitational force, and a position of a center 1a of a light beam effective portion 3 (a position of the optical axis on the lens surface) is displaced (is eccentric) from a position of an outside diameter center 2a of the lens 10 (a center position of a lens outside diameter). Specifically, the center 1a of the light beam effective portion 3 is positioned at an upper side by a distance &bgr; from the outside diameter center 2a of the lens 10.
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