Ikelite 6871.06 Underwater Camera Housing for Canon Digital EOS 6D CameraTTL Flash Exposure: Connection with a TTL sync cord is the most reliable and efficient way to fire an external underwater strobe. The camera's built in flash does not need to fire, providing the extended battery life and zero lag time between exposures. Our proprietary circuitry allows direct communication between the camera and current Ikelite DS Substrobes* for the most accurate through the lens (TTL) metering control of an off camera flash.