A target distance to a system target located at variable distances from an imaging system is determined by illuminating a calibration target at a calibration distance with a collimated light beam during a calibration mode of operation, by illuminating the system target at the variable target distance with the collimated light beam during an imaging mode of operation, by configuring the collimated light beam with a beam spot of a generally constant size during both modes of operation, by capturing return light of a calibration image size from the calibration target during the calibration mode, by capturing return light of a target image size from the system target during the imaging mode, and by determining the variable target distance based on the calibration distance, the calibration image size, and the target image size.