I'm not familiar with the Beseler 23C series myself. My earlier comment about condensers was based on a quick Google that turned up a Craigs' List ad for one that was a condenser. It sounds like yours probably doesn't use the condensers, but you should check your manual (if you've got one) or take the advice of somebody who's more familiar with this model.
Originally Posted by Lawrence Chai
Again, check the manual, if you've got one. I see a lot of comments about ~150W bulbs for many popular enlargers, so it could be your 85W bulb is too dim. (My own enlarger takes three 35W bulbs, but it's a weird one.)
The lens is new and free of fungus as is the bulb (new) which is an 85W halogen type.
That might help -- but as you say, you've got rather long exposure times to start with, so unless/until you improve the brightness out of the enlarger, stopping down may be an awkward solution.
In terms of vignetting, does it happen with wide open apertures? Would I avoid this problem stepping down a few f stops?
I'd expect that would depend on whether the problem is primarily with the diffusion (or condenser) light source or with the lens. You could certainly try it; that might be a useful diagnostic test. Be aware that you'll need to raise the head higher to get an equivalent-sized print when you switch to a longer lens. Since you're talking about an 11x14 print, this will mean a pretty high head height -- perhaps higher than the enlarger supports. Most enlargers let you tilt the head for wall projection or reverse the head to project on the floor for situations like this.
I have a 105mm that I use for my 6x6 enlargement. Would using this lens change things?
There are so many variables from my own equipment and materials that I can't give you a definitive answer. Certainly I wouldn't get many 30-second exposures at f/2.8 to make an 11x14 with my equipment and materials. 30 seconds at f/5.6, perhaps, but not at f/2.8.
Paper used Ilford MG FB glossy. Does 30 seconds sound too long for an adequate exposure for a 11x14 enlargement at 2.8?