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The SU-4 Wireless Remote TTL Flash Controller enables wireless remote flash with automatic TTL or manual exposure control and can be attached to any current Nikon Speedlight and many previous models. The SU-4 detects the firing of the master flash (including built-in Speedlight) and sends a firing start signal to the slave unit, then terminates the firing of the slave flash by detecting firing stop signal. This eliminates the need for a connecting cord. This unit operates effectively up to 23 or 25 feet from the location of the main flash.
