Okay...the midget reflector comes in two styles--a 60 degree smooth bowl, and a 45 degree bowl that has a dimple in the center. When I used these, I used Sylvania Press 25's With what today would be called 200 speed film I shot from 10 feet at f32. These are very powerful bulbs. You can buy them on e-bay for about a dollar apiece, if you look a little. The screw base bulbs mostly have very high guide numbers, because films were slower in the 1930's and they are more expensive.