| 摘要 |
PROBLEM TO BE SOLVED: To provide a highly accurate Fresnel optical element having a long focal distance, capable of observing an observation image with high definition, and an optical system using the same. SOLUTION: Fresnel optical element has a plurality of slopes which transmit and refract or reflect light and of which the variation of the slope angles of the adjacent slopes is fixed. The plurality of slopes are formed by simulating a rotationally symmetric aspheric surface given by the following formula: Z=(Y<SP>2</SP>/R)/[1+ä1-(1+k)Y<SP>2</SP>/R<SP>2</SP>}<SP>1/2</SP>]+aY<SP>4</SP>+bY<SP>6</SP>+cY<SP>8</SP>+dY<SP>10</SP>+..., and -1<k<0, provided that in the Y-Z plane having the Z-axis of the three-axis right-handed rectangular coordinate system as the center axis, R is a paraxial curvature radius; k is a cone constant (conic constant); and a, b, c, and d are each the forth, the sixth, the eighth, and the tenth order aspherical coefficient. The variation of the slope angles is fixed by changing the Fresnel pitch, thereby reducing discontinuity of the image. COPYRIGHT: (C)2011,JPO&INPIT
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