| 摘要 |
PURPOSE:To simplify the construction and improve the accuracy by using a drivable refractive optical element and a photoelectric converting element. CONSTITUTION:In the vicinity of the focal plane of an objective lens 16, a transparent focusing plate 18 having a split-type prism 17 at its center, upon which a frame 19 having a gear 19a on its outer circumference is mounted so that it is made rotatable through a pinion 20 by a motor 21. at the back of the plate 18, a CdS photoconductive cell 25 is arranged through a focusing lens 23 and a porous plate 24. Thus, the light having passed through the lens 16 is focused through the prism 17, the lens 23 and plate 24 upon the cell 25 so that the focal point can be detected when the output of the cell 25 bocomes its maximum. |
