An optical rangefinder based on time-of-flight measurement, radiates pulsed light toward an object (70), and receives reflected light from the object, the
receiver operating in a
photon counting mode, so as to generate a pulse for a detected
photon. There is a variable probability of a
photon detection on the
receiver, and a controller (370, 380, 390; 365, 470, 475, 380, 390; 570, 580, 590, 390) controls the
photon detection probability of the
receiver, based on a
light level. By controlling the detection probability according to a
light level, the receiver can have an increased
dynamic range, and without the expense of using optical components. This can apply even while detecting very weak signals since the receiver can still be in a
photon counting mode while the detection probability is controlled. The
light level can be indicated by an output of the receiver itself, or by another
detector external to the receiver.