| 摘要 |
PURPOSE:To eliminate the adverse influence of vignetting occuring in the size of the pupil diameter of an objective lens and enable accurate detection to be performed by inserting shield plates from the outside circumferential side of reimaging lenses toward the optical axis of the objective lens. CONSTITUTION:When shield plates 5, 5' are inserted from the outside circumferential side of reimaging lenses 3, 3 toward the optical axis of an objective lens 1, part of the luminous fluxes going to 4a, 4c are vignetted by the shield plate 5 on the photo detecting surfaces 4a, 4c of a photoelectric element 4 and the opening angles of a1', a2' a3 and c1', c2, c3 respectively decrease. Simultaneous the luminous fluxes entering the photo detecting surfaces 4'b, 4'c of the photoelectric element 4' are also vignetted. Hence, if the protruding amounts of the shield plates 5, 5' into the photo detecting optical path are so determined that the luminous fluexes vignetted by the shield plates 5, 5', out of the luminous fluxes entering the photo detecting surfaces 4a, 4c, 4'b, 4'c coincide nearly with the luminous fluxes that the luminous fluxes going to the photo detecting surfaces 4b, 4a' are vignetted by the objective lens 1, then the illuminances on the respective photo detecting surfaces of the photoelectric elements 4, 4' become even and the focus detection may be accomplished accurately. |
