| 摘要 |
PURPOSE:To produce interference fringes in arbitraty directions with good accuracy and improve the accuracy of reading by splitting the luminous flux from an object to be detected to two luminous fluxes, and generating diffracted light from one of these luminous fluxes. CONSTITUTION:An optical system 4 forms a focus on a semitransparent plate 7, but since a diffraction grating 8 is placed betweeen an optical system 4 to be detected and a semitransparent plate 7, a number of focuses of different degrees are formed on the plate 7. A focus 0 of zero order and a focus 10 of 1st order form the focus of the wave surface having the aberration on the plate 7, and are so adjusted that a pinhole 12 is located roughly at the center of the focus 10, In this case, the points 9 and 12 where two wave surfaces W1 and W2 are produced are apart in position, and therefore, aberrations are measured in the form of the distortion from the reference interference fringe, and the accuracy is improved. |
