Vignetting (or light falloff...) with Omega B8

[Dusty Negative]

Question: Is it normal that your enlarger does not render a perfect exposure from corner to corner?

Like many of you, I am a completely self-taught analog photographer and darkroom aficionado. I have only ever had one enlarger - it's an Omega B8. It has three condenser lenses - two are in the "main" condenser canister (I'm sure that's not what it's called, but it's the best I can do) while the third, smaller lens sits just under the lamp housing.

This enlarger has always exhibited vignetting or light falloff at the corners. Sometimes, for reasons I cannot yet understand, it is more prominent than at other times.

To try and rectify this, I have fiddled with the top condenser lens (take it out; leave it in; flip it upside down) and I have fiddled with the "canister" (loosening the screws and moving it around). The best combination I've ever found (top lens flat-side up, and canister all the way forward) renders a balanced illumination with about 1/10 stop falloff at each of the four corners. I've never been able to have perfectly equal light throughout the projected area (with the negative holder in). [I am using a light meter to take measurements].

Now, here where the story gets stranger. Even given the 1/10 falloff mentioned above, there's usually one corner that, when enlarging a print, renders close to pure white. This tends to happen in portrait orientation with 6x7 negatives.

I'm thinking there may be more than one thing going wrong here to cause this problem. With the even 1/10 falloff at each of the four corners, I don't think it makes sense to have one or two end up stops brighter at one or two of the corners. That must be something else, but I can't figure out what.

Anyone care to chime in with some thoughts? I've wondered if it could be the negative holder/carrier, but a visual inspection doesn't show anything obviously wrong, although I suppose it might be something I might not catch with my bare eye. The carrier doesn't look damaged.

Help. It's driving me crazy.

 

[Dusty Negative]

 

[ic-racer]

which lens?
which lamp?

Yes, I think as you suspected, may have two things wrong. Condenser not centered over negative and lens not centered over negative.

 

[ic-racer]

To center negative, I point the laser straight up to center of lens (if forms a concentric diffraction pattern). I draw a large X centered below that exact point. Center the easel on that. Now you can fiddle with the negative carrier to get in right in the center of the lens circle.

Then fiddle with the condenser to move it around to center that.

That enlarger should do up to 6x9 when set up correctly.

 

[Dusty Negative]

which lens?
which lamp?

Yes, I think as you suspected, may have two things wrong. Condenser not centered over negative and lens not centered over negative.

By "lens" I assume you mean enlarging lens? It's a Rodenstock Omegaron 90mm, mounted on the 2-inch cone.

Lamp? GE 75watt

Now - "Condenser not centered over negative and lens not centered over negative." OK - please walk me through this. As I mentioned above, the main condenser is in fact not centered over the negative. Reason is that I've only been able to balance the falloff by putting it in its current position. If not, the falloff is unbalanced - for example, 4/10 falloff on one end, 1/10 on the other. But - are you saying that even though I'm balancing falloff I'm creating a secondary problem? I'm not entirely sure how to align the condenser, negative, and enlarging lens. I've never tried pulling the enlarging lens forward (retracting) but I can certainly try that.

 

[Dusty Negative]

To center negative, I point the laser straight up to center of lens (if forms a concentric diffraction pattern). I draw a large X centered below that exact point. Center the easel on that. Now you can fiddle with the negative carrier to get in right in the center of the lens circle.

Then fiddle with the condenser to move it around to center that.

That enlarger should do up to 6x9 when set up correctly.

OH, my. Lasers. OK - looks like I have some studying to do.

 

[Dusty Negative]

To center negative, I point the laser straight up to center of lens (if forms a concentric diffraction pattern). I draw a large X centered below that exact point. Center the easel on that. Now you can fiddle with the negative carrier to get in right in the center of the lens circle.

Then fiddle with the condenser to move it around to center that.

That enlarger should do up to 6x9 when set up correctly.

Is there a "aligning condensers, negatives, and enlarging lenses" for Dummies you can recommend?

 

[Matthew Tapson]

I actually logged on to ask a very similar question about my Omega D5, although when printing 35mm negs I get falloff along one or two edges (and not on every print) and not in the corners like you. I thought it might be alignment though grain seems to be equally sharp across the image so yesterday I aligned the neg carrier, lens and baseboard to within 0.1 degree of each other left to right and front to back using a digital spirit level. I'll do some more printing soon to check whether this has improved the falloff issue.

The opposite corners on your image is strange though. Is the paper flat enough?

I also wondered about using a 50mm on the D5 as I have to use it with the bellows absolutely compacted, maybe an 80mm would be better for 35mm on the D5 unit? Maybe a 105mm on your enlarger would resolve falloff issues?

Here's an example of my falloff problem - more pronounced on the left but present on the right edge as well.

 

[Matthew Tapson]

Is there a "aligning condensers, negatives, and enlarging lenses" for Dummies you can recommend?

The Naked Photographer on Youtube has a few videos on aligning the bigger omegas, might give you some tips: https://www.youtube.com/results?search_query=aligning+the+omega

On my D5, I can adjust the orientation of the surface the negative carrier sits on and make small adjustments to the orientation of the lens mounting system. I used the baseboard as the reference and with a digital spirit level like these ones and reading this sticky on alignment it seems there is a tolerance of about 0.5 degrees at the negative stage in terms of alignment with the lens.

 

[Klaus Mähring]

It helps to use a longer lens, e.g. a 105mm in your case.

 

[Ian C]

Here is the owner’s manual for the Omega B8. The correct condenser layout is given on page 7 for each format and required focal length of lens on pages 7, 8, and 9.

On the top of page 8 the table headed “Recommended Lenses, Lens Mounts and Condensers for Omega B8,” we read that for 3 ½” lenses (90 mm) use the double condensers only (don’t use the smaller supplementary condenser shown at the top of the diagram) when enlarging 6 x 7 cm or 6 x 9 cm negatives.

Note that two different upper supplementarily condensers, 5/8” and 13/16” thicknesses are listed. The only usable configurations are shown in the diagram with either the 5/8” or 13/16” supplementary condenser in the upper position, or without a supplementary condenser as noted in the table and accompanying comments on page 9.



The 90 mm f/4.5 Omegaron is likely the older version of the 90 mm f/4.5 Rodenstock Roganar S (4-element 3-group Tessar design). That should be adequate for 6 x 7 cm enlarging. You’d need a longer lens, say, 105 mm for 6 x 9 cm enlarging.

http://www.prograf.ru/rodenstock/enlarging_en.html

 

[Klaus Mähring]

Here you have a quick illustration why sometimes a longer lens solves the problem of fall off.
The red lines show the angle of a wider lens, and in the case illustrated here the edges are beyond the light source.

 

[MattKing]

I also wondered about using a 50mm on the D5 as I have to use it with the bellows absolutely compacted, maybe an 80mm would be better for 35mm on the D5 unit?

With my D6, I solved this issue with a 60mm lens.
But this does highlight one point - check that the bellows isn't intruding into the light path.

 

[Dusty Negative]

OK - Goodness, so many helpful answers; it will take me a bit to consume all of them properly. Obviously, trying without the supplementary condenser as @Ian C mentioned is the easiest and quickest change. If that doesn't do it, then perhaps I'll try a 105mm as @Klaus Mähring mentioned. Otherwise, time to buy a laser and work on the alignment, and thank you to @Matthew Tapson for the link.

 

[Dusty Negative]

Oh, Lord have mercy. @Ian C - it was the supplementary condenser. I would have laid money down that I had removed it previously to no effect, but I enlarged the exact same print just now and the falloff is gone. I am going to try and salvage the remnants of my pride by saying the resolution must have been due to removing the supplementary condenser AND the work I did yesterday in aligning the main condenser. Yes, yes. That's it. It was both the alignment and the supplementary condenser.

Thank you very much for helping clear up the mystery.

Executive Summary: RTFM!

 

[MattKing]

Oh, Lord have mercy. @Ian C - it was the supplementary condenser. I would have laid money down that I had removed it previously to no effect, but I enlarged the exact same print just now and the falloff is gone. I am going to try and salvage the remnants of my pride by saying the resolution must have been due to removing the supplementary condenser AND the work I did yesterday in aligning the main condenser. Yes, yes. That's it. It was both the alignment and the supplementary condenser.

Thank you very much for helping clear up the mystery.

Executive Summary: RTFM!

So Photrio did its usual good work
Indirectly - very indirectly, we (actually @Ian C ) solved your problem.
And you received some handy additional advice as well.
Glad it worked out.

 

[Dusty Negative]

So Photrio did its usual good work
Indirectly - very indirectly, we (actually @Ian C ) solved your problem.
And you received some handy additional advice as well.
Glad it worked out.

Yes! *And* I avoided having to buy a "LASER" and learn physics & engineering just to get a corner-to-corner print!

(I'll tackle that when I retire)

 

[Matthew Tapson]

With my D6, I solved this issue with a 60mm lens.
But this does highlight one point - check that the bellows isn't intruding into the light path.

Thanks Matt, I'll try enlarging with my 80mm next time