I have an old DII. I am working from memory here, so I hope I get it right. For a 50mm lens, you need a 3 1/2" condenser with a flat lens board. For 75mm - 80mm lens, a 4 1/2" condenser with the flat board. For 90 - 105mm lens, a 5" condenser with a flat board. For a 135mm -160mm lens, the 6 1/2" condenser with the 2 3/4"cone for 135mm lens and the 4 1/2" cone for the 150mm lens. The 4 1/2" and 5 1/2" condenser sets were replaced with a 4 13/16"(?) condenser. I just replaced my head with a variable condenser unit which allows me to just move the supplementary condenser for different focal length lens and only need the 6 1/2' condenser but still need the cones for the longer lenses. I do have a spare 3 1/2" condenser set not being used.