Uneven Illumination Beseler 23cII

[rootberry]

So, I've got this old beseler 23 with an aristo cold light head in it. Everything seems to be working well, except the annoying fact that the illumination is way wonky. I've been a contact printer for ten years, and haven't been enlarging for very long at all, so all of this is pretty mind boggling. Burning in the edges/corners of a negative seems pretty straight forward, but I am getting a triangular shaped falloff that starts pretty far into the negative. What I am asking here is, how to minimize this and diagnose where the problem is coming from.

I'm using a schneider 80mm lens, enlarging 6x6 and I have the light source as close to the negative as possible. Would a change in lens make a difference, and if so what are good options. This is a really old enlarger, so chucking it is also an option.

Maybe you are supposed to lose ~2 stops of light from the center to the edge of the image?

Cheers and thanks for reading my ramble!

 

[chriscrawfordphoto]

There's probably something wrong with the light. Cold lights have a flourescent tube coiled up in them, behind the white diffuser. Old flourescents sometimes only light up on part of the tube...it probably needs a new bulb.

 

[rootberry]

I have checked the bulb, and it lights up the length of the tube, but maybe dimmer in some places. I will have to check that!

 

[George Collier]

Contact Aristo here: customerservice@voltarc.com and describe the problem. You'll probably have to send it to them.
I had fall-off on both sides of my original 4x5 lamp after 20 years of use, and it needed to be replaced. It should be very uniform, one of the advantages of the cold light (you can't see the defects visually).
Also, be sure the proper diffusion plate is between the lamp and the negs. (Mine looks like a piece of white milky plexiglass)