| 摘要 |
1,154,785. Optical objectives. INTERNATIONAL BUSINESS MACHINES CORP. Oct. 5, 1967 [Dec. 8, 1966], No.45431/67. Heading G2J. An objective for use at a plurality of different conjugate object and image distances for different magnification ratios, e.g. for micro-filming in which a reduction of 50X, 40X, 30X, 20X, 17X and 15X is required, comprises a group of lens elements I - VIII and means for changing the effective shape of one lens element V so that a substantial effect is produced only on the coma of the system to permit correction of coma for each of the different conjugate object and image distances. As shown, Fig. 28, the lens V is relatively thin and close to the diaphragm 12 so that its astigmatic contribution is mainly a function of the lens power and almost independent of its shape. Also the spherical aberration changes slowly as a function of bending whereas the coma contribution changes rapidly with bending. Therefore by having a series of lens elements V on a turret 14, each element being of a different shape but all being of similar power, the appropriate one may be introduced into the system for a given magnification, or reduction. To correct for astigmatism the distance S 2 between elements II and III is varied such as by a lead screw 18, the other air spaces remaining constant. Optical data are given for the example shown. |
