PURPOSE: To constitute the lens system for copying which has a small number of lens elements and has aberrations compensated excellently by providing ≥3 groups symmetrically or quasi-symmetrically about a diaphragm, and moving only the inside group for power variation.

CONSTITUTION: This lens system consists of ≥3 groups arranged symmetrically or quasi-symmetrically about the diaphragm, and when the power is varied by varying the conjugation length, the outside group is fixed and the inside group is moved in one body in the optical-axis direction. When the inside group form a positive lens system, the inside group is moved away from the conjugation point and when the inside group constitutes a negative lens system, the inside group is moved toward the conjugation point.