ZOOM LENS SYSTEM FOR PROJECTING MICROFILM WITH SMALL DISTORTION ABERRATION

摘要

PURPOSE:To obtain a zoom lens system compact and with small distortion aberration by constituting lens system of three groups and eight pieces and satisfying specific conditions between intervals between each lens group at the time of variable power. CONSTITUTION:The optical system is constituted of the first lens group I having negative refracting power, the second lens group II having positive refracting power and the third lens group III having negative refracting power in order from the enlargement side. Also, when DS12, DL12 and DS23, DL23 denote an interval between the first group I and the second group II, and an interval between the second group II and the third group III of zoom positions of the shortest focal distance end and the longest focal distance end, respectively, the expression is satisfied. In this regard, a diaphragm S is placed in the vicinity of the second lens group, and at the time of zooming, the first lens group is fixed. In such a way, by a symmetrical lens system, the fluctuation of distortion aberration is reduced, and also the overall length can be shortened.