GB561503A - Improvements in optical systems using plastic lenses - Google Patents

Abstract

561,503. Lenses. COMBINED OPTICAL INDUSTRIES, Ltd., JOHNSON, J., and JEFFREE, J. H. Aug. 11, 1942, No. 11231. [Class 97 (i)] Aberrations of lenses comprising elements made from organic plastic materials and arising from temperature changes of the system as a whole, are offset against one another by the selection and arrangements of the materials for the elements or for their mountings, or both ; the selection may also produce correction for chromatic aberration. Fig. 1 shows elements 1, 2, 3 wherein the element 1 is of crown glass, element 2 of methacrylate ester polymer, and element 3 of polystyrene. Other triplets are described comprising elements of single or mixed plastic materials only. Fig. 6 shows a collective system in which a glass element 17 and an element 18 of methyl-methacrylate polymer are mounted in a tube, 19 of methylmethacrylate polymer, the expansion of which offsets effects of temperature changes in the lens elements ; the tube may extend to the back focal plane, and combinations comprising one element only, and two plastic elements, in such a mounting tube are described. Fig. 7 shows a differential mounting for plastic elements 20, 21, 24, comprising an outer ebonite tube 23 and metal inner tubes 22, 25. Spacing rings of differently expansible materials may be used between lens elements and examples are described. Fig. 11 shows a wide angle anastigmat comprising biconvex methyl methacrylate polymer elements 39, 40 in a tube 41 of the same material fixed in a mount 42, and plano-concave polystyrene elements 43, 44 each mounted in the tube 42 by differentially expansible members 45, 46. Other examples are described.