GB603569A - Improvements in or relating to lens mountings - Google Patents

Abstract

603,569. Lens mounts. INTERNATIONAL POLAROID CORPORATION. May 31, 1944, No. 10492. Convention date, July 14, 1943. [Class 97 (i)] To minimise thermal effects a lens is mounted in a sleeve secured in a housing which engages the opposite end portions of the sleeve, the housing having a coefficient of thermal expansion less than that of the lens. As shown in Fig. 7, the sleeve 44, of synthetic resin, supports lenses 10, 12, also of resin by pins 46 engaging slots in the lens, and is supported in a housing 50 of metal or phenolic resin, which carries a fixed bevel flange 52 engaging a correspondingly bevelled end of the sleeve. The sleeve is pressed against flange 52 by a bevelled ring 54, held by a locking ring 56. The sleeve is so supported as to have a clearance between it and the housing and the bevelled ends of the sleeve are slotted to prevent breakage when expansion takes place. The pin mounting of the lenses permits their expansion relative to the sleeve and the bevels ensure that the lenses remain centred as temperature changes. In a modification the bevels are omitted. The lenses are preferably of the same material as the sleeve and may comprise polycyclohexyl methacrylate, polystyrene or the polymerizable transparent acrylic and methacrylic esters, cyclohexyl methacrylate, methyl methacrylate, alpha phenyl ethyl methacrylate, phenyl methacrylate, benzyl methacrylate, orthomethyl styrene, ortho-chloro styrene, tetrahydro-furfuryl methacrylate and menthyl methacrylate. Lenses of glass may also be used. The lenses may be bonded directly to the sleeve as shown, for example, in Fig. 3, where a bond 28 is formed by pouring synthetic resin through apertures 30 in the sleeve 18a. Alternatively, internal ridges may be formed as the sleeve to which the lens is formed by suitable solvent or the edge of the lens may be cemented directly to the inside of the tube. Example of suitable cements are given. In the modification shown in Fig. 9, a rim 70 of synthetic resin is provided to mount the smaller lens 66 within the resin sleeve 68 which is supported within a housing 80, of a material having a coefficient of expansion differing from that of the sleeve, by fingers 68c carried by reduced ends 68b of the sleeve, the latter being held against a flange 82 by a resilient ring 86 of cork or rubber fixed by a ring 84. These mountings prevent distortion of the lenses with changes of temperature and the sleeve also provides thermal insulation.