A range finder for an automatic camera in which the average total power required for driving the ranging light source is significantly reduced. In accordance with a first aspect of the invention, the intensity of the light emitted by the ranging light source is controlled in accordance with the detected intensity of the reflected light in such a manner that the intensity of light emitted by the light source is reduced to the minimum necessary for carrying out distance calculations. In accordance with a second aspect of the invention, the number of pulses of light emitted from the ranging light source is controlled in accordance with the detected reflected light intensity so that a minimum number of light pulses is emitted consistent with the minimum necessary for carrying out distance calculations.