Ikelite Underwater TTL Housing for Nikon D810The True TTL Advantage: Other housings simply waterproof your camera. An Ikelite TTL housing improves your photos. TTL or "Through The Lens" flash metering means the camera controls flash duration to properly expose an image. Our built in proprietary circuitry tells your camera that a TTL external flash is attached, allowing the camera to adjust exposure more accurately than with slave TTL strobes. Fiber optic slave flash units require the camera's