| 摘要 |
PURPOSE:To improve the focusing accuracy by arranging pyramid prisms on the optical axes of an objective lens and a focusing lens, respectivley. CONSTITUTION:There are arranged on the optical axis 3 of an objective lens 1 and on the optical ascis 4 of a focusing lens 2 in parallel with the former, respectively, both a pyramid prism 5, which has its apex angle larger than two times of the complementrary angle of the critical angle for total reflection so that it is free from the total reflection, and a prism 8 which has a pyramid recess. The lights incident upon the lenses 1 and 2 are focused through the prisms 5 and 8, irises 6 and 9 and focusing lenses 11 and 12 upon light receiving elements 7 and 10. The outputs of the two elements 7 and 10 are fed to a differential amplifier 13 so that a luminous display device 14 is operated, when the difference inbetween becomes zero, to display the focused condition. Thus, sufficient quantities of lights can be fed to the elements 7 and 10 so that the desired objects can be attained. |
