50mm Nikon enlarger lenses

Over the weekend, I was printing in my darkroom. But I have a Nikon 50mm 2.8 lens and I discovered this strange problem with another Nikon 50mm f.4 enlarger lens.

Both lenses for no apparent reason doesn't have a flat field of focus. Luckily, I had a Rodenstock 80mm that I used instead. Does anybody have the same experience with Nikon enlarger lenses and what is causing this issue? BTW, I checked to see if my negative has buckled and it has not.

What did you observe in the lens, projected image or print that led to this conclusion? Presumably whatever it was, it was not present in the Rodenstock?

pentaxuser

pentaxuser said:

What did you observe in the lens, projected image or print that led to this conclusion? Presumably whatever it was, it was not present in the Rodenstock?

pentaxuser

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I noticed yesterday that if I focused the grain focuser in the middle of the easel, the upper left corner was out of focus and when I focused on the left corner, the center was out of focus.

I've used an EL-Nikkor f/4 and several EL-Nikkor f/2.8 lenses, and never seen a problem with curved fields. Several problems may show the symptoms of curved fields. Enlarger alignment is one. Temporary causes of mis-alignment can be anything that prevents lens boards or negative carriers from seating properly. If all four corners of the image are tack sharp and the center is not, the problem is not alignment, but either the lens or the film.

Ah, I type too slow. check all the corners, not just one. If three corners are sharp and the other is not, there might be something causing the film to not lay flat in the negative carrier or the carrier is warped.

I'd suspect enlarger alignment before the lens.....

And negative carrier/holder with glass on the top

locutus said:

I'd suspect enlarger alignment before the lens.....

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It's been a while since I aligned my enlarger. I think it's time to do so.

gorbas said:

And negative carrier/holder with glass on the top

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Thanks for the suggestion, but I don't like carriers with glass. Newtons rings are a real pain and it's more layers of glass I have to keep clean.

Thanks for the reply, Mainecoonmaniac. While you haven't quite said it in so many words I think what you said means that with the same grain focuser, the same negative, the same neg carrier. in fact all things being equal except the change to the Rodenstock, all four corners of the projected image with the Rodenstock are in focus but not with the Nikon.

If all conditions are the same except the lens then it does suggest its a problem with the Nikon lens as unlikely as that appears to be.
I have a 50mm Nikon f2.8 and a 80mm f5.6 Rodenstock and while I have never noticed a difference in the prints from either I cannot focus in the corners with my Paterson focuser due to its design nor have I ever printed larger than 8x10 .

It may be that a grain focuser will pick up a slight problem in flatness whereas the naked eye cannot at the usual print sizes.

If you can test again and confirm your findings you may have a Nikon lens that has for want of a better word a "problem" Whether it is a problem in the real world of prints may be another matter

I have two Paterson focusers, a Major and a Minor. Both are of the same design but the Major is the taller of the focusers to make it easier to use at larger projection - less stooping over the easel. What I have found is that if I focus using the Minor and then use the Major on the same negative I have to move the enlarger bellows very slightly to get the grain to the same point of sharpness. The movement is minimal and does not show up as a difference in the print.

I throw this in simply to demonstrate that under two high magnification grain focusers there is a difference that does not show up on the prints. It may be the same with lenses' tolerances.

pentaxuser

Since the problem does not occur when you change lenses, could it be the lensboard somehow? What happens when you close the lens a couple of stops?

Mainecoonmaniac said:

Over the weekend, I was printing in my darkroom. But I have a Nikon 50mm 2.8 lens and I discovered this strange problem with another Nikon 50mm f.4 enlarger lens.

Both lenses for no apparent reason doesn't have a flat field of focus. Luckily, I had a Rodenstock 80mm that I used instead. Does anybody have the same experience with Nikon enlarger lenses and what is causing this issue? BTW, I checked to see if my negative has buckled and it has not.

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I use EL Nikkors exclusively for all formats and have never experienced this but will now take a closer look.

Enlarger alignment gets my vote as well. Like Ralph I have never had issues with Nikkor EL lenses.

The only way to ensure your neg is flat is to sandwich it in between glass. The slight extra trouble is worth it if you want sharp prints. Like others, I suspect that your enlarger is out of alignment. The most important alignment is the neg stage to the lens stage. Make sure those are parallel.

I doubt that Nikon could not design enlarger lenses without taking field curvature into account...

Dali said:

I doubt that Nikon could not design enlarger lenses without taking field curvature into account...

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I think you're right. It's pretty close to stat camera lenses so the image can't be distorted. But my issue is having part of the projected image out of focus which according to my fellow APUGers, my enlarger is out of alignment.

Mainecoonmaniac said:

I think you're right. It's pretty close to stat camera lenses so the image can't be distorted. But my issue is having part of the projected image out of focus which according to my fellow APUGers, my enlarger is out of alignment.

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Are you sure it's the alignment? You say the 80mm is fine. What enlarger are you using?

Mainecoonmaniac said:

I think you're right. It's pretty close to stat camera lenses so the image can't be distorted. But my issue is having part of the projected image out of focus which according to my fellow APUGers, my enlarger is out of alignment.

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Yes, you can have an issue with 1 lens (NIkkor f/2.8) but with 2 lenses (Nikkor f/2.8 AND f/4), I suspect it comes from something else.

Pieter12 said:

Are you sure it's the alignment? You say the 80mm is fine. What enlarger are you using?

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The print made with my 80mm Rodenstock is sharp edge to edge. However, my enlarger lenses are a 3 lens turret and I'm not sure about the alignment of each lens. Obviously, the 80mm is aligned if enlarger alignment is the issue. I suspect it is.

Not all Photrioers are saying that your enlarger is out of alignment. Those who are saying this can I ask why, if this is the case, is the Rodenstock delivering perfect focus in all four corners?
Dali, I am unsure where your 2 Nikons lenses are coming from. As far as I am aware the OP has mentioned a Nikon 50mm f2.8 and a Rodenstock 80mm f4

Of course, it might be that all things are not equal in terms of the set-up , hence my request that the OP checks everything again and reports back


pentaxuser

pentaxuser said:

Not all Photrioers are saying that your enlarger is out of alignment. Those who are saying this can I ask why, if this is the case, is the Rodenstock delivering perfect focus in all four corners?
Dali, I am unsure where your 2 Nikons lenses are coming from. As far as I am aware the OP has mentioned a Nikon 50mm f2.8 and a Rodenstock 80mm f4

Of course, it might be that all things are not equal in terms of the set-up , hence my request that the OP checks everything again and reports back


pentaxuser

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I'll report what I find. It's my 30+ YO Beseler 45MXT that I bought new. It's like an old friend.

In my experience, the 50mm EL-Nikkors are only good for around 7x magnificaiton, after which the field tends to be opposite the curvature of a negative in the negative carrier. This can be improved by stopping down to f16 and focusing at the correct point, geometrically between the highest and lowest focal points. Usually the center and edges. I use the scale on the enlarger to find the focal center.
One can also use a modification of the Paul Hansma equation to find the aperture also.

N_max ~ 20 / (1 + m) sqrt(dv)

N-max = F number
m = magnification
dv = focusing leeway on the baseboard, represented as the distance on the enlarger column between good focus on the highest and lowest portions of the curved field. (if 'dv' is zero then the field is not curved)
20 = constant for circle of confusion about 0.15mm on the print

In case you don't understand, the focus knob is not used (unless it has a calibrated scale, and I don't know of any like that).

pentaxuser said:

Not all Photrioers are saying that your enlarger is out of alignment. Those who are saying this can I ask why, if this is the case, is the Rodenstock delivering perfect focus in all four corners?
Dali, I am unsure where your 2 Nikons lenses are coming from. As far as I am aware the OP has mentioned a Nikon 50mm f2.8 and a Rodenstock 80mm f4

Of course, it might be that all things are not equal in terms of the set-up , hence my request that the OP checks everything again and reports back


pentaxuser

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"But I have a Nikon 50mm 2.8 lens and I discovered this strange problem with another Nikon 50mm f.4 enlarger lens. Both lenses for no apparent reason doesn't have a flat field of focus."

I think it is pretty clear, no?

ic-racer said:

In my experience, the 50mm EL-Nikkors are only good for around 7x magnificaiton, after which the field tends to be opposite the curvature of a negative in the negative carrier. This can be improved by stopping down to f16 and focusing at the correct point, geometrically between the highest and lowest focal points. Usually the center and edges. I use the scale on the enlarger to find the focal center.
One can also use a modification of the Paul Hansma equation to find the aperture also.

N_max ~ 20 / (1 + m) sqrt(dv)

N-max = F number
m = magnification
dv = focusing leeway on the baseboard, represented as the distance on the enlarger column between good focus on the highest and lowest portions of the curved field. (if 'dv' is zero then the field is not curved)
20 = constant for circle of confusion about 0.15mm on the print

In case you don't understand, the focus knob is not used (unless it has a calibrated scale, and I don't know of any like that).

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Can you expand on this for someone like me whose grasp of the maths is limited. For instance I think I have failed to grasp how to establish the focus leeway. It sounds as if this is done correctlythen this may be key as it appears to eliminate or establish whether the OP's Nikon or is that the projected image from it has any curvature.

Thanks

pentaxuser

Mainecoonmaniac said:

The print made with my 80mm Rodenstock is sharp edge to edge. However, my enlarger lenses are a 3 lens turret and I'm not sure about the alignment of each lens. Obviously, the 80mm is aligned if enlarger alignment is the issue. I suspect it is.

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A three lens turret introduces one more possibility for problems.

ic-racer said:

In my experience, the 50mm EL-Nikkors are only good for around 7x magnificaiton, after which the field tends to be opposite the curvature of a negative in the negative carrier. This can be improved by stopping down to f16 and focusing at the correct point, geometrically between the highest and lowest focal points. . . .

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f/16 is awfully small for a 50mm enlarging lens. Fine grain is less sharp at f/8 than at f/5.6 with the EL-Nikkor f/2.8 that I uaually used. However, smoothing out grain might add to some photos.