>Good question. I don't know a number, but other factors to >consider would include the height and center of gravity of >anything attached to the hotshoe. The stress on the >connection can, and probably will be, much greater when the >camera is turned to shoot in portrait mode and the load then >becomes cantilevered - creating a lot of torque on the >hotshoe.
I understood that it was really going to be a matter of torque rather than weight. But there must be a maximum wieght which, when the camera is in a position to maximize torgue, would be safe. For example a speedlight is going to maximize torque on the hot shoe in certain positions, so I hope if something weighs less than an SB900 speedlight, then it would be safe to mount it on the hot shoe.
Leonard Evens Professor Emeritus, Department of Mathematics, Northwestern University