This is obviously academic if you have an 80mm lens that you can use and gives you sufficient enlargement, but your 50mm lens might be at fault. Were you trying this at full aperture?
Originally Posted by shmalec
Also academic, but isn't the point of the condensers to evenly illuminate the negative? Even a blank negative should add a fair amount of diffusion to the optical path. I would think that would more or less interfere with any optimization of the condensers to match them to the lens-to-negative distance and projecting lens focal length.