Uneven illumination Omega D5XL

[Pieter]

Not really directly about LF, but I posted this on Photrio and I'm want to see what this forum might turn up.

Upon making some 11x14 prints of a scene that has a pretty flat sky, I discovered that one side--one corner especially--is darker (that is the print is lighter) by 1/2 stop or more. This is in comparison to an 8x10 print I made earlier in the week.

Let me explain a couple of things. The original is 2-1/4 square and the 8x10 was made with a 135mm lens, as I like having ample room to dodge & burn between the head and easel. The 11x14 was made with a 90mm lens. Condensor and bellows were adjusted appropriately for each lens. I thought it might be an issue with the lens, so I tried a 105 that I have. Same problem. I then reverted to the original 135 and the hot area no longer showed up on the print, it printed like the 8x10.

Another twist, and I suspect the culprit, is I use a small, halogen bulb instead of the oem one. It gives me a crisper print, sort of part-way to a point light source. I think it might not be perfectly centered in the lamp housing, but I wonder if there is a relatively easy method to check it and line it up.

Thanks in advance for your help and advice.

[Eric Woodbury]

Print without a negative to see if you can make an even tone grey across the field.

[Mark Sampson]

Condenser head or Super-Chromega color head? The color head's diffusion box (if so, which size?) should eliminate most unevenness.
If the variable condenser head, the condensers have to be in the right position for the lens in use.
If the old condenser set, with separate elements, the right condensers must be used.
If you're using a condenser head without the proper (diffuse/opal) enlarger lamp, a #212 or #213, then all bets are off. The condensers were not made for a 'bare filament' lamp.
Omega did make a point-source lamp house that will fit your machine, not common, but they are out there.