Back to the 40 WA Schneider. It will vignette on a condenser. So will the 40 focotar. Later models of the V35 had a double diffuser in the mix box bottom to solve the problem.

I have a 45 Schneider APO ( yes 45, not 40) and it does not vignette, it just goes soft in the corners on a condenser. I thought it was a junk lens until I tried it on a diffusion machine one day. The corners popped right in. Still don`t understand it and I have tried it on multilple condensers known to work properly and other diffusions with the same results.