TTL or "Through-The-Lens" flash metering means the camera controls flash duration to properly expose an image. Unlike fiber optic systems, which attempt to copy the behavior of the camera's built-in flash, this unique housing for the Canon EOS 100D Rebel SL1 provides direct, electrical transmission of this TTL signal to the any current model Ikelite DS strobe.
Since the camera is talking directly to the strobe, the camera's built-in flash does not need to fire. This dramatically increases battery life and virtually eliminates the recycle lag, allowing the camera to be triggered in more rapid succession than with optical-based systems. When shooting a fast moving object, this make the difference between going home with the shot or just talking about it. Additionally, in-line communication between the strobe and the camera completely eliminates signal interference and false triggering caused by light rays bouncing off the water's surface or your buddy's flash going off.The Ikelite-style electrical bulkhead is widely recognized as the most reliable waterproof strobe sync connection available