My Omega D6XL condenser head has three lenses in the condenser. Two very large and heavy convex one side facing eachother and one convex facing down on top of the top lens that is on an adjustable bracket. The adjustment settings are for the focal length of the enlarging lens. There are settings for 50, 80, 105 and 150. It seems to work equally well at 16mm through 4x5.
Frank