I have installed a Zone VI cold light in my ancient but solid Omega D-2 and found slight vignetting on 4x5 negs. Burning the edges cures the problem but I would rather not. Has anyone else had this a problem and is there a solution such as using a longer lens? I currently have a 135 Rodagon 5.6.
I had the same problem with my B8. Rigged the diffuser and now, no vignetting. I actually put the diffuser/piece of round, snowy plastic, between the negative carrier and the "cone" that rests on the carrier. Light leaks, but works for me for now.
There was a review about 15-20 years ago in Darkroom magazine of the Zone VI coldlite head. I believe that the review was written by Ctein. He noted that the head vignetted with the use of a 135mm lens in printing 4x5 negatives.
Zone VI was started by a gentleman by the name of Fred Picker. He was capable of being quite 'crusty'. outspoken and combative. He was also a skilled photgrapher.
He wrote a letter to Darkroom magazine stating that the fault was entirely due to the 135mm lens being used. He stated that using a 150mm lens would have coImpletely eliminated this problem. He was more than generous in offering the opinion that anyone but an idiot would know that a 135mm focal length enlarging lens is too short to properly cover a 4x5 negative. Please understand that I am paraphrasing based upon a article read long ago. The remarks about a 135mm lens not being able to cover a 4x5 negative is NOT a position I support.
However, since the Mr Picker was certainly in a good position to know his product's capabilities I would strongly recommend that you try a 150mm enlarging lens and see if the problem disappears.