Abstract: A wide-aperture array, used to sonically measure range to a source, is calibrated by providing a beam of optical energy from a first location, rigidly affixed to a first end sensor of a trio of array sensors, through a lens at a second location rigidly affixed to a middle one of the trio of sensors, to an optical sensor of the retinal type at a third location, rigidly affixed to the remaining sensor, at the opposite end of an initially straight line from the first sensor, and then measuring the deviation of the beam at the retinal sensor due to deviation of the sensors from positions on a straight line. The wavefront curvature found for any energy received by the array sensors is corrected by the measured deviation.