| 摘要 |
PURPOSE:To maintain lens performance and to obtain a lens system having high temperature resistance, by fixing a plastic lens with low temperature resistance in a lens frame without altering its shape, and correcting variation in refractive index with temperature. CONSTITUTION:The 1st lens 35 uses a normal glass lens and the 2nd lens 30 uses a plastic lens. The 1st lens 35 abuts on a 1st-lens barrel joining part 33 by being fittied in a 1st-lens fitting part 34, and is then fixed to the lens frame 31 by screwing a presser ring 32 into the lens frame 31 while threadably engaging a screw part 21 cut in the outer circumferential surface of the 1st-lens presser ring 32 with the 1st-lens frame screw part 28 cut in the inner circumferential surface of the lens frame 31. When the whole of the optical system is exposed to a high-temperature (or low-temperature) atmosphere after the optical system is assembled in a holder at room temperature, the 2nd plastic lens 30 varies in refractive index and a lens body 38 varies in radius of curvature (shape change) to cause the focus movement of the optical system. |
