ZOOM LENS SYSTEM FOR PROJECTING MICROFILM WITH SMALL DISTORTION ABERRATION

摘要

PURPOSE:To obtain a lens system compact and with small distortion aberration by constituting the lens system of lenses of three groups and seven pieces, and positioning the center of curvature of the lens face of a first and a third lens groups at the side of a second lens group from each lens face apex. CONSTITUTION:The lens 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, a position of the center of curvature of the lens face of the first and the third lens groups I, III is positioned at the side of the second lens group from each lens face apex. In case of variable power, the variable power to a zoom position of the longest focal distance end and the shortest focal distance end is executed by fixing the first lens group I and increasing monotonously the interval of the second and the third lens groups. Therefore, by forming a symmetrical lens system, the fluctuation of distortion aberration is reduced, and also, by fixing the first lens group I, the overall length can be shortened.