I only have a view camera but it it sounds as if Mike is interested in using the roll back on press cameras. In that case, if you plan to use the rangefinder, light leaks wouldn't be as much of a problem. If you actually notice a problem, a little electrical tape in the appropriate spots when you clamp the back on, would easily solve it. I'm going to try some felt or camera foam on mine as a simpler, more permanent solution. It would seem that the biggest problem on a press camera would be framing. You would still need to pay attention to advancing the film and cocking the shutter as two separate operations.