Optical system for copying having temperature compensating lens

Abstract

Abstract PURPOSE: To prevent the degradation in image quality owing to a change in temp. by compensating the rate of change in the focal length of the 1st positive lens with with a change in temp. of a positive lens-negative lens type perfectly symmetrical lens by the rates of change in the focal length with a change in the temp. of the 2nd negative lens. CONSTITUTION: From object side, the 1st positive lens, the 2nd negative lens, the 3rd negtaive lens and the 4th positive lens are successively disposed, wherein the 1st and 4th as well as the 2nd and 3rd lenses are the same, thereby forming a transmission type perfectly symmetrical imaging lens system. From the object side, the 1st plsitive lens, the 2nd negative lens and a reflecting mirror are successively disposed, thereby constituting a reflection type perfectly symmetrical imaging lens system. In such perfectly symmetrical lens system, the rates of the change in the focal length occuring in the adjacent positive lens and negative lens are offset each other between both lenses, whereby the rate of the change in the focal length in the entire lens system is kept at a small value. COPYRIGHT: (C)1982,JPO&Japio

Inventors

• 👤 Michihiro Tokuhara

Bibliographic Details