Patent ID: 6124985
Filing Date: 2000-09-26
Classification: G02B

Abstract:
A zoom magnifier consisting of a positive first lens group, a negative second lens group and a positive third lens group, in this order from the eye side,wherein zooming is performed by moving said second lens group in the optical axis direction;wherein said third lens group has at least one aspherical lens element in which at least one aspheric surface is provided on either surface, and said aspheric surface satisfies the following:(a) if a paraxial spherical surface is convex, a power of said aspherical surface weakens in a peripheral area of said aspherical surface compared with said paraxial spherical surface; and(b) if a paraxial spherical surface is concave, a power of said aspherical surface strengthens in a peripheral area of said aspherical surface compared with said paraxial spherical surface;wherein the magnifier is an observation optical system; andwherein said zoom magnifier satisfies the following conditions:30 mm<f.sub.I-0.35<f.sub.II /f.sub.I <-0.2 and0.3<L/f.sub.I <0.6whereinf.sub.I designates the focal length of said first lens group;f.sub.II designates the focal length of said second lens group; andL designates the distance between said first lens group and said second lens group at the lowest magnification.