I changed enlarger lens and...

Jorge Oliveira · Nov 19, 2003

Hello,

I use an old Opemus III enlarger (6x6) for 35mm work (the condensers are not adjustable).
My main lenses are 50/2.8 (Nikkor and Computar), but the head does not rises enought to allow for cropping in 24x30 cm format.

So, I went after a 40/4 (in 'the' auction site) and, while the lens is quite decent and gave me the extra size I was looking for, there's an unusual problem when I mount it: an faint halo out of the image area.

Any clues on what is causing it or how to correct it?

Thanks,

Jorge O

Robert · Nov 20, 2003

Is the halo all around? Or to one side? My guess is light is leaking from some place. Not sure why the change of lens would cause it. Is the lensmount a little smaller?

MikeK · Nov 20, 2003

I think the problem is with the fixed condenser. I have the same problem when printing 35mm negatives on my 4x5 D2 with the 4x5 condensors in place. I somewhat solved the problem by placing a sheet of diffused glass on the negative stage. It went away completely when I installed a cold light head.

- Mike

ann · Nov 20, 2003

I would agree with the condensor not being correct. I.E. with a Besler 23 C a circle of light will occur when the condensor stage and lens size donot match.

Robert · Nov 20, 2003

That doesn't make any sense to me. My Omega can't change condensors and is perfectly happy making 35mm prints when setup for 6x6. My Beseler doesn't complain either when I forget to change things. At least I don't think so.

Wouldn't a 35mm negative used with a 6x6 setup really be no different then cropping a 6x6 negative?

Jorge Oliveira · Nov 20, 2003

Thanks, guys

- The lens mount is the same - just unscrew one and screw the other. They have almost the same flange to neg distance.
That was one of the reasons I've purchased the Nikkor and not a Componon that was in Ebay at the same time, the Componon needed a shorter distance that the enlarger would not allow (and the Nikkor ended cheaper .

- It may quite well be the condensers. There's no way out of it, since as I've posted, the condenser assembly does not have any adjustment. But I can try the diffuser (there's one and I'm not using it)

Jorge O

Jorge Oliveira · Nov 20, 2003

Robert

Do you change the lens when enlarging 35mm?

The interesting point is that with the 50mm there's no halo, only with the 40mm (that is a wide angle lens for 35mm).

Jorge O

ann · Nov 20, 2003

i will try a 40 mm in one of our Omega enlargers this weekend when I go into the lab and get back to you. I know the beseler's will create a halo when not in the correct positon, but am not sure about the Omega, as we usually change the condenser position when changing lens, or the others have a cold light head which covers up to 4x5 negatives.

dr bob · Nov 20, 2003

I have a separate condenser assembly for 35mm on my Omega II. It really only inceases the light intensity and coverage - slightly. I was wondering if the Nikon lens could be producing some internal reflections which might be producing your halo? How far out side the image area is this halo? If it is far enough, why worry about it?

Truly, dr bob.

P.S. I also have a Nikon 50mm lens from another enlarger which I can try to see if it reproduces your observations if you wish - I'll have to spend a small effort to locate and mount it, but will be glad to try....

Robert · Nov 20, 2003

I norrmally change lenses.

Lets think about this. What do the condensors do? They focus the light onto the negative. With the enlarger setup for 6x6 the light is focused to 6x6. Most of that should just be hitting the negative carrier with 35mm.

The only thing I can suggest is put the lens cap on the lens and turn the enlarger on. Do you still see the image? If you do then you've got some sort of leak.

I don't have a 40mm to test here but I just tried 35mm with the enlarger set for 6x6. Nothing I could see.

clogz · Nov 20, 2003

Hello Jorge,
You might try adjusting the distance between the light bulb and the condenser.

All the best

Jorge Oliveira · Nov 20, 2003

Thanks, everyone.
I will try to assemble the bathlab tomorrow (or during the weekend) and do some tests.
Will post any findings.

Jorge O

glbeas · Nov 20, 2003

I would check out the lens thoroughly. What you describe makes me think of some serious internal reflections in the lens. Do you notice any change in the contrast of the print image from this lens to the old one?
Then again this may be from light reflected from the inner surfaces of the bellows and making its way through the lens to the easel. In that case I'd think you have a heck of a lens.

MikeK · Nov 20, 2003

The condenser focuses the light to the center of the enlarging lens. So for a 6x6 condensor you are using either a 75mm or 80mm lens. When you switch lenses for a smaller format the condenser will still focus the light for the longer lens. This will be exaggerated with a 40mm (wide angle lens) as the focus point will be ~40mm beyond the lens. This is going to show up as a weird light source outside the image area. It will not be as exaggerated with a 50mm lens.

Did you notice you had to rack the lens a whole lot closer to the negative stage to focus the negative?

- Mike

Thilo Schmid · Nov 21, 2003

Jorge, your condensor must match two parameters: the focal length of the lens and the magnification ratio. Although there is always only one "ideal" combination, practice has some tolerances. If your combination is out of these bounds, you will get an uneven illumination. Your halo is a simple light fall-off. You need a condensor suitable for a 40mm lens.

Ole · Nov 21, 2003

I have the same (?) halo on my Opemus 6 with colour head, using both 50mm and 80mm Anaret-S lenses. Since I use a colour head, the condensors are not to blame.

But that halo has never given me any problems...

Jorge Oliveira · Nov 21, 2003

I did not do any test yet, but since you guys are very cooperative:

dr bob
Thanks for the offer. If my tests do not show anything, I will take it;

glbeas
Looking at the lens it looks fine, and enlargements (did not do a side to side compare) are fine;

Mike
No, technically I did not have to. That's one of the reasons I've bought the Nikkor - it has the same flange to negative distance of the 50mm (but the glass protudes more in the back, so it's really closer to the neg).

And thanks also for all other posts.

Jorge O

Jorge Oliveira · Nov 21, 2003

Ok, guys

I've put on my Sherlock cap, lit the pipe and :?:

- The light comes out through the lens - not a leak somewhere else.
- The 'halo' is only visible when the red filter is in place; it's actually light coming out of the lens at such a wide angle that it overpass the red filter assembly (much larger light circle than the working area);
- It gets stronger the smaller the printing is, and disappears (or I simply can't see it) at large enlargements, with any of my 3 lens;
- At the smallest enlargement possible (head fully down), the Computar 50/2.8 is the worst, the Nikkor 40/4 is second and the Nikkor 50/2.8 is the best, halo wise.

I've tried using only one condenser lens in both possible positions, but then the light circle was too small.

Solutions:

- I will use the 40/4 only for enlargements larger than the 50/2.8 are capable of (that was the original intention, BTW).
- I will paint mate black the lens mounting ring (I had to order a custom one since the original part would not accept a lens when mounted inverted, and 'tomorrow I will paint it', you know...). ops:

Thanks again,

Jorge O

Ed Sukach · Nov 21, 2003

Jorge Oliveira said:
- I will paint mate black the lens mounting ring (I had to order a custom one since the original part would not accept a lens when mounted inverted, and 'tomorrow I will paint it', you know...).

??? "Inverted"?? Are you saying that you are using this lens with the front element towards the film - and not the enlarging paper?

Jorge Oliveira · Nov 22, 2003

Ed

No, not the lens.
The mounting plate is not flat - it has a recess, to be used like this ---___--- for the

75/80mm lens and you invert it like this __----__ for shorter lens, otherwise it won't focus.

But the lens would not fit (inside the recess) when I tried to screw the lens on, so I had to order a new custom machined mounting plate.

My sorely missed Durst had similar mounting plates, but since they were wider, there was no problem using them.

Jorge O

Jorge Oliveira · Nov 23, 2003

Just to let you know that I've painted the mounting plate (it's more like a ring) matt black.

Not much of a change, but there was a minor improvement (the 'halo' seems dimmer).

So, looks like a case of the condensers not been optimized for 40/50mm lenses (and this is true, since it's a 6x6 enlarger).

Jorge O

V. 'ESCU · Jan 6, 2004

Opemus uses both concave and convex mounted lens boards. In the case of a 50mm or smaller focal length, you screw the lens to the concave side of the board. But if the lens is too large, it will screw only partially (if it does at all) into the board, allowing the light to escape around the thread. It happened to me with a Minolta lens, which is a large model. This doesnt happen with the 75-90mm lenses, as you screw them to the convex side of the lens board, and in this case the lens size doesnt matter.

Jorge Oliveira · Jan 6, 2004

It's not my case.

The original lens board wouldn't even allow mounting the EL-Nikkors (defective part).
I had to order a custom machined lens board, and the lens screws fully in this one.

Thanks,

Jorge O

cesarb · Jan 6, 2004

Salve Jorge,

As I have always played with Durst enlargers, from 6x6cm to 5x7', soon I learned that one can't fool around with optical geometry (as an engineer, I suppose you know what I mean). With Durst bigger enlargers one needs to check both condensors, their distance from lens, bulb size and position on XYZ space, magnification and, if one really wants to be precise, the filament position inside de bulb. Once it's all set, light distribution is so even as it can be.
Regarding to Opemus III, I could suggest you try both ways: 60mm lens and 1- turning the head for floor projection or 2- using a wood block 10/15cm high under the column, so to allow 30x40cm projection on the board.
BTW, as I'm also brazilian, feel free to e-mail if you want. Certo?

Cesar Barreto

Jorge Oliveira · Jan 6, 2004

Ola, Cesar

The Opemus III is in phase of replacemet by an Opemus 6 I found in Germany's Ebay and that a friendly soul over there is reshipping it for me (German sellers usually do not ship out of Germany).

Abraços,

Jorge O

I changed enlarger lens and...

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