| 摘要 |
PURPOSE:To decrease generation of aberrations with respect to axial and offaxial condensing points by satisfying sinusoidal conditions as well as the time of designing the annular zonal boundary radii of respective Fresnel zones. CONSTITUTION:The 1st and 2nd Fresnel zones 31, 32 co-possessing the optical axis on both faces on the spot light source side and condensing point side of a parallel flat plate 3a and are so designed that the annular zonal boundary radii r1,k and r2,k (k=1,2,3...) of the 1st and 2nd Fresnel zones 31, 32 satisfy the following two conditions: The luminous flux emitted from the spot light source placed at a prescribed distance from the plate 3a on the optical axis is condensed without aberrations to the condensing point on the optical axis. The luminous flux emitted from the spot light source off the optical axis deviated in the direction perpendicular to the optical axis from the spot light source on the optical axis is condensed without aberrations to the condensing point off the optical axis deviated in the direction perpendicular to the optical axis from the condensing point on the optical axis. Even the object point deviated from the optical axis of the Fresnel zones is thereby condensed to the image point with substantially no aberrations. |
