| 摘要 |
PURPOSE: To provide a Fresnel lens which decreases stray light, prevents the loss of light and can make the entire part bright. CONSTITUTION: In the Fresnel lens having plano-convex positive power, of which light incident face is formed as plane 1, and of which prism lens part 2 having a lens face 4 and non-lens part 5 is formed on the light exiting face, the angle of inclination of the non-lens face 5 of the prism lens part 2 is set within a range of the angle formed by the direction of the incident main rays on the inside of the lens and the direction of the main rays emitted outside the lens. Then, the margins of the angleθ1 formed by the incident rays on the inside of the lens with the non-lens faces 5 and the angleθ2 formed by the rays emitted outside the lens are generated and, therefore, even if the rays from the points slightly deviated from the optical axis arrive at the non-lens faces 5, the rays are emitted nearly along the optical axis and the stray light by the non-lens faces 5 is decreased. The loss of the light is thereby prevented and the entire part is made bright.
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