I use a simple and cheap 18-70mm for my studio work, that is happiest at f/9 so that's where I set my lights up for and it gives a useful DoF, unless the ambient is really bright when I go out to f/11 with no real noticable loss in sharpness but by f/16 you can just about see things are not so razor sharp. As Gary said way back in the thread set everything up then turn off your radio trigger and take a shot... if it's black great, if not close the aperture a third of a stop and wind up your lighting by a third of a stop and try again. BTW I set my shutter at 1/160th to be sure not to exceed the radio trigger sync