| 摘要 |
PURPOSE:To obviate the change of light power even if the focal length of a plastic lens changes with ambient temp. by providing a diffusion plate which receives the light from a light receiving element with the rear surface and transmits light to the plastic lens from the front surface as a uniform surface light source. CONSTITUTION:The diffusion plate 3 is installed between the lens 1 and the light emitting element 2. Said light receives the light generated like a spot from the element 2 on the rear surface and transmits the light to the lens 1 from the front surface as the uniform surface light source. The diffusion plate 3 is formed of, for example, ground glass, white plastic plate or bubble lens plate of which the front surface is worked to a special shape so as to uniformly diffuse light. Since the light from the element 2 which is point light emission is emitted as panel light by the diffusion plate 3, change of the opening angle betaby the deviation in the focal position of the lens is extremely small even if the focal position of the lens deviates to F1 or F3. The plastic lens is, therefore, so constructed that the light power outputted therefrom does not change in spite of a change of the focal length thereof by the ambient temp. The ray type sensor having high measurement accuracy is thus obtd.
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