The Triggertrap Mobile app is no slouch, and if you really want to dip your toes in the world of high speed photography, you will want to avoid your camera’s shutter lag. How? Easy: Trigger your flash directly.
The Triggertrap Flash Adapter lets you do just that. The Triggertrap Flash Adapter connects your flash to your iPhone, iPad, iPod Touch or Android device so you can trigger it with the Triggertrap Mobile app.
Video explaining how it works and why is better then connecting the cable directly to your DSLR: