The G-III features a 40 mm f/1.7 with six elements in four groups. Rangefinder focusing with Automatic shutter option and manual settings. The light meter requires a battery installed at the bottom of the unit in order to function. The integrated lightmeter provides shutter priority and manual modes. The sensor is located on the forward part of the lens, which allows use of filters without manual compensation of exposure. The Canonet can use standard flashes, or the Canonlite D which was custom-designed for the Canonet.