Beseler 23C uneven illumination

[VinceInMT]

I've been chasing this problem for a while and am stuck so I am coming to the group mind for some direction. My 23C is in very good condition. I am getting an uneven illumination that shows in prints as a lighter area in the side of the print that is toward the front of the baseboard when it is exposed. I have checked the alignment. I have removed the filter tray. I do have a heat absorbing glass above where the tray was. I am using a Schneider 80/5.6 Companon that appears clear. I have new bulb. I am using the correct condenser setting for 6x6. The condenser lenses look clean. The drawer for the red filter is fully retracted.

I stopped lens way down and did a test with no negative in the carrier. This is a scan of an 8x10 print.:

The lighter area on the left was aligned with the front of the baseboard. Next I made this print, straight, no manipulation, from a 6x6 negative.

I turned the negative around in the enlarger and printed it again.

Note how the lightness has move to the other side. This side, the right, was aligned with the front of the baseboard.

For reference, here is a scan of the negative:

I changed the lens to a Schneider Componar 50/4.5, moved the condenser to the 35mm position, and switched to 35mm negative. Here is a scan of an 8x10 print.

Again, the left side of the print was aligned with the front of the baseboard and show a little lighter. I flipped the negative around and made another print.

Again, the lighter area moved to the other side of the print, the side toward the front of the baseboard.

So, what is going on here? I'd had a problem a while back where the internal coating of the Eiko bulb flaked off inside the bulb and that definitely gave me an uneven illumination. I replaced it with another Eiko bulb. Things were better but it was still uneven. Before these tests shown here I replaced the Eiko with an Osram bulb. I am running out of ideas. What do you think?

Thanks.

 

[xkaes]

It's been a while since I used a 23C, but what bulb type is it -- 211, 212, etc. ????

Are you sure the alignment of the lens stage and negative stage and condenser stage are OK?

Perhaps one of the condenser elements has moved slightly. It should have small tabs holding them in place.

 

[Kino]

Just throwing a few things out here...

Has the negative carrier been filed and does it have a shiny side on the aperture?

When you reorient the negative, do you keep the carrier in the same position or rotate it?

Does your lens board have the illumination rod hole? Has it been covered with a red gel that might have faded to allow light through?

Have you inspected the bellows to see if something is loose and hanging down into the light path?

 

[eli griggs]

Clean your condenser, and if it was in a smoker's darkroom,;clean it again and then do ALL the lenses.

I was a heavy smoker for 14 years and way back, in a friend's darkroom which I freelanced printed in, I started having similar issues with prints on the condenser head of a 4"x5" enlarger, caused by the accumulation of smoke's filth, the lenses too.

Windex, with ammonia, which is very good, removes the tars, etc, with several good cleanings, using soft, old tee shirt material, never paper towels, shop towels, or any paper, period.

Even if your kit has never been near a smoker, do a thorough cleaning of all optics and include the inside of the condenser head and the diffuser.

This focus s the first step to running down whatever your issue is.

 

[ic-racer]

Most enlargers will have uneven illumination. You are on the right track to now know the characteristics of your system by making that print.

First thing, however, is the condenser system is designed, not necessarily to match a lens focal length, but to match a certain distance from the condensers. For example a small print with a short lens might need the same condenser combination as a large print from a long lens; if the lensboard is at the same position in both cases.

So, did you have the head and lens stage at a reasonable enlargement and was the lens focused at the imaginary negative plane? These things will change the illumination pattern. Stopping down was good! No lens wide-open will be even.

 

[ic-racer]

When you indicate you 'checked alignment' you probably made the lensboard and baseboard parallel, yes? But did you make sure the center of the bulb, the condensers, the center of the negative holder and the lens are 'on center' or all lined up. The master printer will check and adjust or file and bend as needed to make this perfect.

 

[ic-racer]

This was my first 8x10 light source, before and after I made a center filter from the print to counterbalance it. Eventually sold that head and got a Durst head. In the 'Pre-LED' era, Durst was the leader in even illumination.

To make the filter, I scanned the print and printed that out on transparency sheet with my inkjet printer. This was a diffusion head, and I put the 'filter' between the diffuser and the negative.

The result is not perfect, but most prints will be improved by being a little dark around the edges, rather than being a little light. So it was a huge improvement.

 

[Sirius Glass]

As posted above, look at alignment issues: the lamp in the center of the optics, optics stacked vertically and in line and not askew, ...

 

[MattKing]

The fact that flipping the negative around causes the lighter area to move is intriguing.

 

[albada]

If possible, try rotating the bulb 180 degrees. If the light area also rotates, then you know what the problem is: uneven light from bulb, or bulb is askew.

In a condenser system, the light shining on the baseboard is actually an image of the surface of the bulb. Thus, the advice above to check the center-alignment of the optics and bulb is wise.

Mark

 

[Sirius Glass]

The board has to be level and the column vertical, check both with a spirit level.

 

[Kino]

OP doesn't state if the negative was removed and flipped in the carrier or if the carrier was rotated to reorient the image.

Simply removing the negative, reorienting it and re-inserting it into the holder in the same position is a very different proposition than if they rotated the negative carrier.

Condenser or stage alignment issues would cause the illumination problem to remain in the same spot if the carrier was not reoriented.

Conversely, I would think that it would require a pretty substantial misalignment of the negative carrier stage to the lamphouse to cause the spot to move if the carrier were rotated between exposures. Something like one edge of the negative carrier being stationed in the optical center of the condenser output.

It almost sounds like an incorrect negative carrier is being used; one that is not centered on the optical path...

 

[ic-racer]

Also, note this from Post Exposure 2nd Edition.

 

[warden]

Also, note this from Post Exposure 2nd Edition.
View attachment 326894

Wow. Time to clean my condenser, which I’ve done maybe once in 10 years.

 

[VinceInMT]

That is for all your suggestions. I’ll give them a try and get back to you.

Oh, and when I turned the negative around, I put the carrier back in the same way.

 

[Pieter12]

Can you check and adjust the light bulb alignment? I had this problem with an Omega D5. Also, although a workaround rather than a fix, you can try using a longer focal length lens than the format calls for. Thus you would just be using the center of the field hand have less fall-off. It limits the smallest enlargement you can make though, don't know if that is problematic.

 

[MattKing]

Oh, and when I turned the negative around, I put the carrier back in the same way.

Is it a glass carrier?

 

[Kino]

Curiouser and curiouser!

 

[VinceInMT]

Is it a glass carrier?

No. The reason I turned the negative around was to see if the lighter area would move to the other side of the print, which it did which points to and enlarger issue rather than a film one.

 

[VinceInMT]

OK, a bit of an update. I did some work on the enlarger. I took the condenser apart and gave the lenses a good cleaning, although they looked pretty good anyway. I was going to take that suggestion and turn the bulb around but it has printing on the other side so I left it, for now, the way it was. However, I did pull the bulb mounting bracket out and filed out the slots that the screws go through to give me more adjustment, allowing the bulb to move forward a bit more. I also played around with the centering of the condenser, adding a small spacer, about 3/16” to the back, bringing it forward a little.

I made another print, see the negative scan above, and did it with no filters:

It’s still a bit lighter on the right. I made another printer, using the split-grade approach and burning the left side in about 1 stop and the right side just a little.

I guess it is what it is. I can’t see what else can be done to even out the light other than printing a filter, which I might try. BTW, I suspect that my filters might be a partial issue as they are decades old. I use 6x6 ones in the filter draw above the condenser and just ordered a new set.

 

[VinceInMT]

To make the filter, I scanned the print and printed that out on transparency sheet with my inkjet printer. This was a diffusion head, and I put the 'filter' between the diffuser and the negative.

The result is not perfect, but most prints will be improved by being a little dark around the edges, rather than being a little light. So it was a huge improvement.

I will try something similar. Thanks.

 

[xkaes]

It's also possible that the light bulb in the condenser head is too high or too low inside the head. I don't know what would cause that, but it's something to check if all else fails.

 

[MattKing]

Try turning the bulb to the other side - writing and all. If you see a change in evenness, you may just need to replace the PH111 bulb.

 

[eli griggs]

At this point, you might try making the enlargement of that negative on someone else's enlarger, to see if it's the negative itself or no.

After that, consider looking for a dicro colour head for the unit, which should do away with the need of gel filters, completely.

Post a Wanted ad here and elsewhere and see what KEH, et al have on offer.

Cheers.

 

[VinceInMT]

At this point, you might try making the enlargement of that negative on someone else's enlarger, to see if it's the negative itself or no.

After that, consider looking for a dicro colour head for the unit, which should do away with the need of gel filters, completely.

Post a Wanted ad here and elsewhere and see what KEH, et al have on offer.

Cheers.

Since I scanned the negative I have a pretty good idea that it’s not the negative. I do, sort of, have access to another enlarger at the local university where I am an alumni. And I did think about a different head but, I’ve had this enlarger since 1976 and it’s worked just fine until this recent problem. What I find puzzling, and intriguing, is that it’s not like this is an electronic or a wear issue as the enlarger is pretty simple so I really want to get to the bottom of it.