| 摘要 |
PURPOSE:To perform changeover and selection of narrow and wide visual fields through simple operation by making only the secondary mirror part of an afocal optical system changeable to the inside and outside of the visual field of a focal optical system. CONSTITUTION:The secondary mirror 42 of an afocal optical system is made rotatable 90 deg. about the rotating axis 45 orthogonal to optical axis in nearly the intermediate position of a reflecting mirror 421 and a correcting lens 422. Then, the infrared rays from the target enters at a visual field T and is reflected by a concave primary mirror 41, after which it is reflected and condensed to parallel luminous fluxes by the secondary mirror 42. The parallel fluxes then enter the lens 1 having a standard visual field S of a focal optical system and is forcused to a specified position F by the movement and adjusting of the lens 1 to the optical axis direction. When the secondary mirror 42 is turned to the positions 421', 422' of the reflecting mirror 421 and correcting lens 422, the infrared rays directly enter the lens 1 through the opposing clearance of both positions 421', 422' and observation of the standard visual field S becomes feasible. |
