Abstract: Two light beams capable of interference with each other are applied to an area sensor while they are inclined to each other. The area sensor reads a pattern of interference fringes formed by the two light beams. The read interference fringe pattern is subjected to a Fourier transform, and then an inclination-related component is removed therefrom. Thereafter, an inverse Fourier transform is effected. The shape of the wavefront of light to be measured is determined on the basis of a phase difference between the two light beams which is known from the result of the inverse Fourier transform.

Abstract: A device for optically measuring an aspheric surface includes a fringe-scanning shearing interferometer for applying a wavefront of illuminating light to the aspheric surface and optically measuring the aspheric surface based on light reflected by the aspheric surface along a measurement optical path. A plurality of ring filters having respective different light-transmitting areas are successively positionable, one at a time, in the illuminating light and outside of the measurement optical path for applying divided portions of the wavefront of illuminating light successively to the aspheric surface. The radius of curvature of the wavefront of illuminating light applied to the aspheric surface is measured.

Abstract: A method of measuring the origin and amount of a shear between a basic light beam and a reference light beam in a shearing interferometric system. To detect the shear origin, shutters are disposed respectively in the optical paths of the basic and reference light beams. The basic and reference light beams are guided through a condenser lens toward a four-segment light detector. First, the optical path of the reference light beam is closed to allow only the basic light beam to fall on the four-segment light detector. By adjusting the position of the light detector, the position of the basic light beam is identified. Then, the optical path of the basic light beam is closed to allow only the reference light beam to reach the light detector. While output signals from the light detector are being monitored, a shearing member is displaced to shift the reference light beam to detect the shear origin in which the reference and basic light beams are overlapped.

Abstract: A focusing method for interferometer wherein a light flux passing through a converter lens for converting the shape of wave fronts is caused to be incident on a tested surface and a testing light beam reflected by the tested surface is caused to be incident on a light receiving element capable of measuring the distribution of intensity of the light at least one-dimensionally. The tested surface is moved in the direction of its center axis until it reaches a position in which the vertex of the tested surface coincides with the focus of the converter lens and the output of the light receiving element shows a peak value, and the tested surface is further moved, from the position referred to hereinabove which serves as a reference position, in the direction of its center axis.