| 摘要 |
PURPOSE:To attain reduction and enlargement almost to unmagnification while holding an object plane and an image plane constant by moving the whole system to the object plane and image plane while varying the gap between the 1st lens group having positive focal length and the 2nd lens group symmetrical with it. CONSTITUTION:The 1st lens group G1 includes two positive lenses L1 and L2 and one negative lens L3 from the object side and the 2nd lens group G2 includes one negative lens L4 and two positive lenses L5 and L6 from the object side symmetrically with the 1st lens group G1; and both groups G1 and G2 are positioned halfway between the object plane and image plane at the time of unmagnification and the system has symmetrical arrangement on the whole. Further, inequalities I -III hold. Consequently, reduction and enlargement are performed about to unmagnification while the object plane and image plane are held constant, so that the variable power optical system which maintains stable image forming performance is realized. |
