VARIABLE POWER TYPE OBSERVATION OPTICAL SYSTEM AND VARIABLE POWER TYPE EYEPIECE LENS SYSTEM

摘要

PROBLEM TO BE SOLVED: To obtain a variable power type eyepiece lens system which is short in an overall length, is small in the change rate of the overall length accompanying variable power, is well corrected in various aberrations, is simple in constitution and is lower in a cost by providing the optical system with a first lens group of positive power and biconvex and biconcave second and third lens groups of an aspherical face on one face, executing variable power by moving the second and third lens groups in directions opposite to each other and having specific conditions satisfied. SOLUTION: This optical system has the first lens group G1 of positive power which is the combined lens of a negative lens 11 and a positive lens 12, the second lens group G2 of a biconvex single lens 13 made of plastic in which the one face is the aspherical face and the third lens group G3 of a biconcave single lens 14. The variable power that the second lens group G2 moves near to the first lens group G1 and that the third lens group G3 parts from the first lens group G1 is executed to satisfy the equation; 1.5<ΔLD/M<3.0 and the equation; 1.8