Precision passive range measurement.

Image feature analysis to determine object distance can provide precision performance if the optical point-spread function is highly sensitive to range. In the method presented here, a specially designed mask imparts a quarter-wave phase shift over part of the input aperture, thereby inducing an interference effect with maximum sensitivity. The resultant image can be compared with a conventional image through deconvolution and least-squares fitting in order to extract a precise range estimate. This method is quantitatively examined through computer modeling and laboratory testing and is broadly applicable to a wide range of optical wave bands.