| 摘要 |
PURPOSE:To vary an incident light quantity to each photodetector by a movement of a condensed point of a reflected light corresponding to a distance to a point to be measured, from a lens, by making a light incident to one photodetector and the other detector by a total reflecting surface in a pin-hole mirror, and a pin-hole. CONSTITUTION:A reflected light is focused by a lens 3, and a pin-hole mirror 4 is inclined and installed between a condensing lens 15 and a photodetector 5 installed on an optical axis of the reflected light, and the lens 3. The pin-hole mirror 4 has a total reflecting surface and also has a pin-hole at the optical axis position of the reflected light. When a point to be measured is at a distance D+DELTAD, a condensed point P by the lens 3 of the reflected light is a pin- hole in the pin-hole mirror 4, and accordingly, the reflected light is all made incident to the photodetector 5. Therefore, a normalized output VA/(VA+VB) in the operating part becomes ''1''. When the distance to the point to be measured becomes short, as for the position of the condensed point P, a light which does not pass through the pin-hole in the pin-hole mirror 4 is reflected by the total reflecting surface and made incident to the other photodetector 6. Accordingly, a value of VA/(VA+VB) becomes small. |
