I do the same as winger does above... I use the 105 rodenstock rodagon (older version)... it's a 39mm opening... I have no trouble switching with a nikon 50mm 2.8. I use it with 6x7... I print onto 11x14 as well... All that lensboard does is ensure that the part of the lens that sticks into the enlarger head doesn't hit the insides (negative) above it. as you move the focuser closer to it. Although you already probably figured that out.