Light falloff w/ 90mm on 6x7 negative

lifein2x3 · May 1, 2007

This is the best light coverage I can get on a 6x7cm frame with a 90mm lens; this particular shot is stopped down to f8, where I do most of my printing. The frame in this photo is an intentionally blown out transparency; I don't have a 6x7 carrier, so I have to use an old 6x9 carrier with a mask.

I'm getting around this by using a 105mm lens for now, but I can't print 16x20 with that focal length (not enough height, I'm using a Dead Link Removed.)

Am I incorrect in thinking a 90mm lens should cover all of a 6x7 frame? Or are my condesner lenses screwy? I've always done 6x6 up to now, so I've never noticed a problem with the 90mm lens and a standard 150 watt tungsten light source, but I'm thinking a diffuse light source might be the way to go.

Any suggestions?

MikeK · May 1, 2007

I am not sure that a 90mm wil cover 6x7; I use a 100mm or 105mm lens. But do you have the condensor set for this format. It looks to me that could be the culprit. Cannot remember but for a smaller format you raise the condensor and for larger formats you lower it. When new this enlarger came with a scale that sat on the right hand side showing the settings for 35mm, 6x7, 6x9 and 4x5.

You might want to try adjusting by hand until you get even coverage

Hope this helps

Mike

lifein2x3 · May 1, 2007

Sorry, I should have been a bit more specific. I did adjust through the entire range of avaliable distance between the light source and the negative plane, and this was the best I could do at 90mm. It doesn't get more even than that.

MikeK · May 1, 2007

Hmm then it must be the lens. You might have to go with a 100mm or 105mm and maybe make a drop table for the head assembly. That way you are lowering the baseboard - more stable way to go than extending the height of the head.

When making giant enlargements I rotate the column of my enlarger and project down to the floor

Sorry I could not be more helpful

Mike

lifein2x3 · May 1, 2007

Oh, you were. I had a feeling the lens wasn't long enough, but needed some second opinions.

I'm half-tempted to rip apart the Rube Goldberg setup I have and add more height between the table and the base of the enlarger frame, or see about a table that can drop out for more distance.

The thought of swinging the head 90º to project on the wall gives me headaches, but may be the only way to go. I'd just need to figure out how to attach a 16x20 Speed Ezel to the wall. :-\

Allen Friday · May 1, 2007

My main travel camera is a Mamiya 7II and I have been printing 6x7 negatives for the past 10 years or so on a Zone VI enlarger with a cold light. I use a 4/80 Schneider/Kreuznach lens. It has plenty of coverage. I would think that a 90 would have more, not less.

I suspect that your problem has to do with something other than the lens.

Travis Nunn · May 1, 2007

Since I've had my RB67, I've used a 80mm Nikon lens and a 80mm Rodenstock lens in conjunction with 3 different enlargers (Beseler, Saunders and Omega) for my 6x7 negs. Plenty of coverage with everyone.

lifein2x3 · May 2, 2007

If the problem isn't the lens, could it be the light source? I have a feeling the condenser lenses aren't the original lenses. One is slightly blue heat-resistant glass, the other is a bit thicker and is neutral in color.

Would switching to a diffuser light source be a possible solution, and if so, what should I look for?

Roger Hicks · May 2, 2007

lifein2x3 said:
Am I incorrect in thinking a 90mm lens should cover all of a 6x7 frame?

I've never encountered a 90 that won't cover 6x7 -- we print 6x9 wth a 90 Computar -- but there's no reason why a 90 HAS to cover, and if it's not a condenser problem, I can't see much else it can be. Can you borrow another lens anywhere to compare it?

Cheers,

R.

RoBBo · May 2, 2007

As far as enlarging lenses go, for the most part, their focal length will tend to have a lot more to do with their coverage power than you'd see in other uses, where a 90mm can have wildly different coverage depending on it's source.
However, just because it's 'more uniform' doesn't mean it's totally uniform, and a lenses coverage power depends much on the lens design and not on the focal length.
It might not just be that it's 'a 90mm' just that it's THAT 90mm.
My 80mm Nikkor covers 6x7 on both my 23CII and my 45M with no problem.
For the most part it's pretty safe to assume a 90mm SHOULD cover 6x7, but, different manufacturers, different lens designs...and you end up in the situation you have now.
An 80mm Nikkor can be had on ebay for not all that much, and while there's plenty of other lenses of the same approximate length that will allow the coverage you're looking for without sacrificing your enlargement possibilities, I think the Nikkor does that best (Pretty sure the Rodenstocks with the same coverage are 90mm?)

One question I'm surprised no one has asked yet, is what lens are you using on there? You said it's a 90mm but that's really not enough information to determine if it has the coverage you want.
Find out what the problem is before you go spending money trying to fix it, if the problem is in your lens and you buy a cold head, it'll still be in your lens.

Nick Zentena · May 2, 2007

What 90mm lens do you have? I doubt it's the issue but you never know. Like others I use an 80mm Nikon just fine.

It might be the light source setup. I doubt the condensors have been changed. On my Beseler the things are a matched unit.

At what setup is the light best? You tried them all?

My guess is the enlarger isn't setup right some how. Not the lens.

ricksplace · May 2, 2007

I get good coverage with a 80/4 Componon and with a 75/4.5 Ektar on both a 23C and a 45MX, so long as the condensers are set for the LENS used, not the film size. (eg. set the condenser for 80mm/6X6 even if you are using a 6X7 neg).

Steve Smith · May 2, 2007

RoBBo said:
It might not just be that it's 'a 90mm' just that it's THAT 90mm.

I agree with this. When I bought an RB67, I also bought a 105mm enlarging lens as I had been using a Componon 80mm for everything up to 6x6.

Although the 105mm is fine, I ran out of room when doing a large print due to a low ceiling so I went back to the 80mm lens which worked fine.

Steve.

lifein2x3 · May 2, 2007

RoBBo said:
It might not just be that it's 'a 90mm' just that it's THAT 90mm. My 80mm Nikkor covers 6x7 on both my 23CII and my 45M with no problem.
...
One question I'm surprised no one has asked yet, is what lens are you using on there? You said it's a 90mm but that's really not enough information to determine if it has the coverage you want.
Find out what the problem is before you go spending money trying to fix it, if the problem is in your lens and you buy a cold head, it'll still be in your lens.

The lens is a Wollensak Raptar 90mm f4.5. I talked to the guy I got both the enlarger, lens, carrier and Mamiya RB67 from, and he said he didn't have problems with that setup before, so I'm assuming I've done something, maybe I need to re-arrange the condenser lenses. I did take it apart when I moved into my current apartment last summer.

There's a solution there, I just need to find it.

Ryuji · May 2, 2007

Like ricksplace said above, the condenser and the light source position are adjusted for the lens. The condenser should focus the light source at the place (entrance pupil to be exact) of the lens in its normal enlarging position. Set up the enlarger so that you get the image focused on the easel. Take the negative and the lens off. Do you see the light source focusing around the position of the lens? If not, you should adjust the condenser and/or the light source position.

Like Roger said, I've never seen a 80mm that doesn't cover 6x7. I use Componon 80/4 and 105/4 (or was it 5.6) at one stop down from wide open, but the lens covers a lot. I think the problem is the light source and condenser configuration.

PHOTOTONE · May 3, 2007

Something that wasn't mentioned yet, but with the condenser head, are you using a true "opal" type of bulb in the head? A household light bulb will not give even illumination, no matter what. A Wollensak Raptar is not a top notch enlarger lens, it too may just not have enough coverage, but a 90mm lens in general should cover 6x7 just fine with a condenser head.

Roger Hicks · May 3, 2007

One further thought is that as far as I can see, the corners of the paper are illuminated, so the lens ain't the problem: it has to be the light source, hence the dark ring. I can't believe I didn't think of this before.

Cheers,

R.

Nick Zentena · May 3, 2007

I think the light source allows the light bulb to be moved up/down for adjustment. Could that be it?

lifein2x3 · May 3, 2007

Nick, I've covered the entire range of movement, this is the best it could do.

Roger, I was thinking that myself, since the dark band seems to take the same shape as the bulb; I was wondering if the condeser lenses might have gotten mixed up when I moved (I also moved a 23 CII, and packed the lenses in the same box.) I doubt it's the bulb, I have the same 150 watt enlarger bulb that's been in there since I've had the enlarger.

juan · May 3, 2007

I was going to suggest reversing the condenser lenses. I have a Berkeley Omega in which one lens has to go on top and the other on the bottom - they don't work properly reversed, although I can't remember what problem reversal causes.

Also are they oriented the correct way - the curved surfaces should probably face in on both.
juan

PHOTOTONE · May 3, 2007

I have had several 45 series condensor enlargers, and now I still use a 45 series, but with a diffusion color head. The condenser assembly holds two condensers in a large cast circular cylinder. Both flat sides of the glass condenser lenses should be facing out, with the curved sides facing in towards each other. I believe the condensers are identical. When you photographed the light pattern as an example of coverage did you have your lens focused on the negative plane (the space where the negative would go)?

The inside of the lamphouse should all be painted flat black, is yours? I think also the inside of the cast cylinder that the condensers are held in is also flat black.

PHOTOTONE · May 3, 2007

Also, in the condenser cylinder is a spacer that spaces the condenser lenses apart so they do not touch.

Ryuji · May 3, 2007

Are your condensers marked with any info? If you moved around the light source and couldn't get better than this, I think the most logical problem is the mismatch of the lens and the condenser. I also noted that you can get a decent image with 105mm with the same negative format.

I am a Durst user and my main gear is Laborator 138S. I use it with anywhere from 50mm to 210mm lens, and every time I change the lens I have to change the condensers. 80mm lens is pretty tricky. Some other lenses are fine with wrong condensers but not 80mm for some reason. Each condenser element is marked with focal length or model number, at least in the case of Laborator 138 series and Laborator 1200, and the instruction manual has a table of lens focal length and condenser focal length that are matched.

lifein2x3 · May 6, 2007

I've run the light and condenser through the entire range of available adjustments. There are no marked pre-sets, I've always run an empty negative carrier for the format I need to get the coverage right.

The photos I posted are the best coverage I've been able to get. The entire negative area is covered by the light, the problem is that dark ring; the light isn't even.

The condenser is set up exactly the way it should be, the two lenses are separated by the large collar and are both facing inward (flat edges facing out). The only thing I'm missing is the piece of heat resistant glass, it broke not long after I got the enlarger. I do have the smaller collar that separated it from the top condenser lens in place just to keep everything together.

The light bulb I'm using is a GE PH-1212, 150 watt bulb. This is the same bulb that came with the enlarger, and I'm assuming it's an "opal" type. It's heavily frosted and the printing is on the side of the bulb, not the top.

Also, using a Schneider Componon 105mm lens with the same negative gives me perfectly even illumination across the entire frame. It could just be that the Wollensak 90mm lens is for crap and I need to look into a drop table for the enlarger instead of the table I've got it mounted on now.

Ryuji · May 7, 2007

How many kinds of condenser lenses were made for your enlarger? Usually, multiformat enlargers have several sets of condensers that need to be switched when switching the lens' focal length.

Light falloff w/ 90mm on 6x7 negative

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