| 摘要 |
PURPOSE:To increase NA(numerical aperture) and to compensate an off-axis aberration sufficiently by decreasing for increasing positive or negative refracting power according to the distance of an aspherical surface from an optical axis when the refracting power of a paraxial curvature at the peak of the aspherical surface is positive or negative. CONSTITUTION:One of a lens element which is arranged most closely to an object side and lens elements which are arranged behind said lens element and include a cemented lens is provided with the aspherical surface. Namely, when the refracting power of the paraxial curvature surface at the peak of the aspherical surface, the aspherical surfaces is so shaped as to decrease in the positive refracting power according to the distance of the aspherical surface from the optical axis and when the refracting power of the paraxial curvature surface is negative, the aspherical surface is so shaped as to decrease the negative refracting power. In a front group, this aspherical surface is provided. Consequently, the NA is made large and on-axis to off-axis aberrations are compensated excellently although the constitution is simple. |
