Used Ikelite 6146.02 Canon G1X Mark II Underwater Waterproof Camera HousingTrue Canon TTL Exposure: TTL or "Through The Lens" flash metering means the strobe interprets information from the camera to control flash duration and properly expose an image. TTL may be accomplished directly through electrical signals from the camera, or indirectly through watching the behavior of the camera's built in flash. Circuitry built into this housing allows the camera to communicate directly with compatible underwater strobes (see Strobe