A simple imaging range sensor is described, based on the measurement of focal error, as described by A. Pentland (1982 and 1987). The current implementation can produce range over a 1 m/sup 3/ workspace with a measured standard error of 2.5% (4.5 significant bits of data). The system is implemented using relatively inexpensive commercial image-processing equipment. Experience shows that this ranging technique can be both economical and practical for tasks which require quick and reliable but coarse estimates of range. Examples of such tasks are initial target acquisition or obtaining the initial coarse estimate of stereo disparity in a coarse-to-fine stereo algorithm. >