JPH05296879

PURPOSE:To improve the precision in measurement of a spatial frequency characteristic of an optical system to be inspected, by measuring transmission wavefront aberrations at an arbitrary position and positions taken by rotations at angles of 90 and 180 degrees around the optical axis of the optical system and by executing operational processings. CONSTITUTION:On the occasion of measurement of MTF (spatial frequency characteristic) of an optical system 2 to be inspected, the transmission wavefront aberration of the optical system 2 is measured by an interferometer part 3 while the optical system 2 is rotated by an rotating mechanism 4. First, aberration WA is obtained at an arbitrary position around the optical axis and aberration WB and aberration WC are obtained at positions taken by rotations at angles of 90 and 180 degrees respectively. The transmission wavefront aberrations thus determined are subjected to computations of WAS=(WA-WB)/2 and WCM=(WA-WV)/2 by an arithmetic part 6 and also these WA, WAS and WCM are subjected to the development of Zernike. As to the coefficient of Zernike developed, a spherical aberration component is extracted from WA, an astigmatic component from WAS and a core part from WCM. The wave-front aberration is computed from the coefficient of Zernike extracted and the MTF is determined thereby and displayed in a display part 7.