| 摘要 |
PROBLEM TO BE SOLVED: To provide a fresnel lens capable of improving use efficiency of obliquely incident light beam to a first surface from the outside, and reducing stray light.SOLUTION: The fresnel lens is characterized in that on a non-lens surface 22, for a flat surface E including a symmetry line M and a focal point F, a first generatrix 22aclose to the focal point F is on a straight line T passing through a cross point of a boundary line 23c and the flat surface E, and the focal point F, with two points as a boundary, obtained by back-projecting, onto the boundary line 23c, two intersection points R and S formed by dropping a perpendicular line V onto a projection line L from a midpoint Q on the symmetry line M of the projection line L formed by the boundary line 23c of an orbicular zone 23 with respect to a reference plane G parallel with an image surface I and in contact with a first surface 10. The non-lens surface 22 satisfies the condition of -arcsin(1/n)≤&thetas;≤&pgr;/2-2arcsin(1/n) regarding a second generatrix 22afarther from the focal point F, where n is refraction index of a lens material and &thetas;[rad] is angle of inclination opposing to a focal point F side with respect to a normal line H of a point D closest to the cross point of the boundary line 23c and the flat surface E among points on the first surface 10 in the flat surface E. |
