Thanks for the post Brian.
I picked up a D2 a year ago (my first enlarger) with no manual and the two condensors it came with were both stacked together. So I've used it that way ever since. Works great with my 105mm on a flat board and my 135 on a cone. however my 50mm lens vignettes.
I'll have to try one of the condensors all by it's lonesome and see what happens..
I rarely print my 35mm negs bigger than 5x7 so it's rarely been an issue to just use my 105.
LOL Fools rush in where angels fear to tread.