| 摘要 |
PURPOSE:To obtain a bright index image with high contrast, by utilizing a polarizing prism, thereby eliminating substantially almost all the decrease in amount of light from an index, and eliminating almost all the flares. CONSTITUTION:A back surface mirror 15 is constituted as a 1/4 wavelength plate, whose one surface is a reflecting surface. Therefore, linearly polarized light, which is inputted to the back surface mirror 15, is reflected as linearly polarized light, which is crossed at a right angle with said linearly polarized light. The light is reflected by a polarizing prism 14 after passing through a total reflection prism 6 and directed to the center of a sphere of a decentering measuring surface of a lens to be checked 9 through an image forming lens 8. The decentering measuring surface of the lens to be checked 9 is located at a position of auto-collimation. Therefore, the linearly polarized light, which is reflected by the decentering measuring surface goes in the reverse direction. The light is reflected by the polarization prism 14, reflected by the back surface mirror 15 through the total reflection prism 6, and then inputted to the polarization prism 14 through the total reflection prism 6 again. Since the polarizing direction is rotated by 90 degrees, the light is transmitted. The linearly polarized light transmitted through the polarization prism 14 is reflected by an index plate 13. Since the light passes the 1/4 wavelength plate twice, the polarizing direction is rotated by 90 degrees. |
