There really is an app for everything for the iPhone. If you are the sort that likes to take pictures you can get apps that will work for checking the light levels in the room so you can get the perfect exposure. The problem is if you use a big camera that needs two hands to operate is that you can’t hold the camera and the iPhone at once.
A guy named Nigel has solved that problem with a creation he made using hobby plastic, glue, and a sharp knife. He cut the plastic so it would slide into the hotshoe mount on top of his DSLR. He then glued the parts together and made a holder that he can put his iPhone into.
The holder keeps the iPhone on top of the camera a like a giant flash. By combining this mount with the iTunes Pocket Light Meter app, he can aim the camera where he wants to shoot and look at the iPhone to see the light in the room. This is a cool little project if you’re into photography for sure.