| 摘要 |
PURPOSE:To prevent a lowering of a condensing characteristic due to dew condensation by providing a venting open groove for allowing the air of a facing part to communicate with the open air. CONSTITUTION:A condensing lens 3 is mounted to a housing so that the facing part 3c thereof fronts on the opening of the housing and the photodetector provided in the housing is arranged to the condensing point of the lens 3 and venting open grooves 10a, 10b for allowing the air in the facing part 3c to communicate with the open air are provided to the surface opposed to the housing of the lens 3. Since the convection of the air in the facing part 3c and the open air is achieved through said venting open grooves 10a, 10b, the temp. difference between the outer surface of the lens 3 and the facing part 3c is reduced and a lowering of a condensing characteristic due to dew condensation can be prevented. Since the open grooves 10a, 10b are opened laterally on the housing side, the venting opening parts are inconspicuous and appearance is not damaged. |
