Uneven print exposure

[rrusso]

I replaced the 50mm lens with an 80mm on my Beseler 23CII Dichro, using the same lens board (I only have one).

On all of the prints I've made, there is an underexposed section across the edges. It's not an even vignette, but a "strip" on the prints, top and bottom, but not the sides. At first I thought it was the negs, but they are fine.

I think I may know what's wrong, but it's too late to test my possible fix tonight, so I figured I'd throw it out to you guys to see if you think I may be on the right track. Or maybe this problem has come up before...

So... my dichro head has a 6x9 mixing chamber, the "6" measurement running top to bottom, and the "9" measurement running side to side, as you stand facing enlarger. The "6" area happens to be where the underexposed sections are. The lens board has two bolts, one on each side, which appear to act as stand-offs. The board is removed by pushing in and then tilting down - there is a pressure spring at the back. The two bolts appear to be the only means of adjustment, and I'm thinking they are used to move the lens either closer to or farther away from the light. So, maybe the lens is too far away, causing fall-off...

 

[MattKing]

It doesn't sound like the centre of the light path corresponds with the centre of the lens.

 

[Sirius Glass]

Start by checking the enlarger alignment.

 

[btaylor]

My 23C is in storage so I can't check it, but my 45 mxt is up and running-- on the 45 there is a bellows adjustment above the negative stage for different sized negatives, if it's in the wrong position it can cause what I think you are describing. Download a PDF of the manual and check instructions for adjusting to different sized negatives.