Focal-length measurement by multiple-beam shearing interferometry

The application of multiple-beam shearing interferometry to lens focal-leng th measurement is described. A coated shearing plate interferometer was use d in transmission to produce sharp multiple-beam fringes that rotate as the collimation of the incoming wave front from the lens under test changes. T he test lens was used to collimate light from a point source that was trans lated longitudinally, and the focal length was determined from the rate of rotation of the fringes as the source moved. This method is simple, accurat e, and lends itself to automatic determination of focal length. (C) 1999 Op tical Society of America. OCIS codes: 120.0120, 120.3180, 120.4610, 220.114 0, 220.3630, 220.4840.