I just had a lesson from the school of hard knocks regarding lens mount sizes. I bought a Bogen 22A enlarger on E-Bay. It uses the standard 39mm thread size lens. It came with a 50mm lens (focal length) already mounted in the enlarger. The first time I tried to make prints with it, I couldn't get the size of the image to fill my 8x10 easel, even with the head at the top of the column. I knew that the Bogen 22A had the capability of making 11x14's, even cropped 11x14's. I called two local camera shops and they gave me possible causes that ranged from condenser elements in backwards to a problem with the bellows. I didn't really buy any of them. I took the lens out and it turned out that I had a 25mm thread size lens mounted in a 39mm thread size adapter and the adapter was mounted in the enlarger. I wondered if the extra space that the adapter added might have been the problem with my image size. So, on a hunch, I got back on E-Bay and found a Voss 50mm lens with the 39mm thread size and bought it. I mounted the lens directly into the enlarger and it works fine. I can now make enlargements as big as the column will allow, larger than 11x14. The adapter was the problem. Stay away from them!!!!