Optical examination apparatus particularly useful as a Fizeau interferometer and schlieren device

Claim 1

Optical examination apparatus for determining properties of an object, comprising: a point source of light producing a diverging beam of direct light; a first optical system located such that, when it includes the object to be examined and receives the beam of direct light, it retraces the light in the form of a converging beam of reflected light from the examined object back towards the point source of light; means for intercepting the converging beam of reflected light; a viewing device; a second optical system located to receive said intercepted beam of reflected light, to collimate it, and to direct the collimated beam to said viewing device; said first optical system including a partial transmittance reference plate, whereby a contour map of the object topography is obtained from the interference between the direct light beam and the reflected light beam; said second optical system including a schlieren filter at the focal point of the reflected beam to cut down the Fourier transform of the image, whereby a schlieren image is produced at said viewing device; and means for selectively locating said partial transmittance reference plate or said schlieren filter in its respective position in said first and second optical systems.