| 摘要 |
PURPOSE:To cancel 'trend' to wavelength of the difference between the AF in-focus position and a full-aperture in-focus position of a photographic lens by placing the optical axis of a divided optical element in a position more distant from a principal optical axis than the aperture center of a diaphragm. CONSTITUTION:The optical axis of a divided optical element 5 is deviated from the principal optical axis outward more than the aperture center of a diaphragm 4 by a prescribed extent DELTAh5-4. This prescribed extent, namely, the extent DELTAh5-4 of eccentricity is so determined that 1<=delta<2 is satisfied when delta=(gamma4.DELTAh5-4)/(gamma7.DELTAh4) is defined where r4 is the radius of curvature of an auxiliary lens 3 and r7 is the radius of curvature of the divided optical element 5 and DELTAh4 is the extent of eccentricity of the aperture center of the diaphragm 4. The radius of curvature is positive for a convex, and the extent of eccentricity is positive in the direction of going away from the optical axis (principal optical axis) of a condenser lens and the auxiliary lens. Thus, the lateral chromatic aberration in an optical system is eliminated, and further, 'trend' of the chromatic aberration of the photographic lens is canceled. |
