The ELD is the only camera fully compatible because of the contacts on the back of the body. The 503ex and the 503cw are compatible if you have the special synch/release cords made by Kodak, works very good. For other applications such as view camera or flexbody you will need the special synch/release made only by the Kapture Group. This is only for the Proback Plus. The one called Proback will work only on the camera it was designed to fit. The synch/release is no longer a stock item since the back is discontinued, but they may be able to make one up for you. As it happens I have a spare that I will sell if you are interested.