The SU-4 Wireless Remote TTL Flash Controller enables wireless remote flash with automatic TTL or manual exposure control. It can be attached to any current Nikon Speedlight and many previous models. When in use 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 it terminates the firing of the slave flash by detecting firing stop signal totally eliminating the need for connecting cord.

Operates effectively up to 23 or 25 feet from location of the main flash.