Can I use the St-E2 to trigger a studio flash unit and avoid having to attach a wire to my cameras PC socket?
A15: Yes, but with a little modification. The basic problem is that while the near IR output of the ST-E2 is quite sufficient to trigger the optical sensors on most studio flash heads, the studio flash systems mistake the initial transmission of control data that the ST-E2 sends out to the Slaves as the signal to fire. So when the camera body sends the fire all Slaves command out via the ST-E2, and releases the shutter, the studio slaves have already fired but not yet recycled enough to fire again. The result is an underexposed or black frame. The solution lies in something as simple as a small piece of paper. By inserting a piece of paper in the hotshoe as you slide the ST-E2 in place, you can cover the four side contacts, while leaving the center contact exposed. This has the effect of turning whatever is mounted on the hotshoe into a non-ETTL device. Indeed, it is the center contact that would be used to fire the studio strobes if your camera lacked a PC socket, and a hotshoe to PC
