| 摘要 |
PURPOSE:To perform measurement with good accuracy, by changing over an interference system by opening and closing a plurality of the shutters in a beam path when the non-spherical degree of the surface of an object to be measured is large and when the non-spherical degree is small or said surface is flat and spherical. CONSTITUTION:When a lens 58 has a non-spherical surface, only a shutter 58 is closed and a shearing interferometer is constituted. The reflected beam emitted from a laser beam source 1 to irradiate the lens 58 is split into two beams by a splitter 59 through a splitter 53, and the measuring beam and the reference beam respectively pass through mirrors 62, 61 to reach a TV camera 67 through a lens 66. The mirror 62 is minutely vibrated by a means 64 to perform fringe scanning. When the lens 58 has a spherical surface only a shutter 57 is closed and a fringe scanning Twyman-Green interferometer is constituted. The reflected beam split by the splitter 53 is reflected by a mirror 69 to become reference beam and transmitted beam is reflected by the lens 58 to become data beam; both beams reach the TV camera 67. The mirror 69 is minutely displaced by an electrostriction element 70 to perform fringe scanning. By this method, measuring accuracy is enhanced.
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