Diagnosing a lousy enlarging lens: How do I know if I've got one?

I had the chance to print a few 16x20's from some 35mm negs, and I'm wondering if I've hit the wall with my enlarging lens, a decades-old El-Nikkor 50/2.8.

First, I thought it was my camera lens: one side of the frame was acceptably sharp (not great, just acceptable) and the opposite side was soft. I quickly realized that the grain itself was soft, hence the soft image. Focusing for sharpness on the right side threw out the left, and vice-versa, and the middle was never sharp when the edges were. I suspected that my decades-old Beseler 23C was out of true, so I fiddled with the lens assembly at the bottom of the bellows, shifting left and right with limited improvement.

Sorry I'm being so long-winded here, but could I have a bum enlarging lens? A close exam shows haze and other crap in the lens, but I never noticed any trouble at 8x10 printing, so I ignored it. Does 16x20 bring out all the flaws that have been lurking all this time?

And on a related note, does an enlarging lens have depth-of-field like a camera lens? If I stop down to f8, say, do I get better d-o-f and sharper grain, even if my eyeballed focus is off?

Thank you for your help. My Rodenstock Omegaron 75 does not seem to have similar difficulties...or if it does, the smaller enlarging ratio disguises it better at 16x20.

Your enlarger is probably a bit out of alignment. You may need to adjust it to get the whole image sharp, especially at that size.

Depth of field on the enlarger works the same as on the camera. Smaller apertures have more.

16x20 is big. It's hard to get the whole image sharp without stopping the lens way down. Last time I printed 11x14 from 35mm, I actually set the lens at f/22 and made 10-minute exposures. You will get better sharpness, though, by using a larger aperture if you can manage to get the image focused.

...and how would one adjust an enlarger's alignment, exactly?

Thanks for the authoritative info! Does one adjust an enlarger simply by eye (seems loosey-goosey that way) or do you put a level or a square against the lens board, kind of the way you'd true a table-saw? Am I looking for an exact 90º angle between the lens board and the upright, and an exact 90°from the upright to the easel surface?

You should search the forum for enlarger alignment. Some people think you have to have a micro-precise laser tool to align an enlarger.

The main thing for sharpness is that the negative and the lens are square to each other. The easy way to check is to get a scrap negative and put scratches in each corner, then check it with the grain magnifier to make sure all the corners are sharp. Also, make sure your negatives aren't moving when they get hot. That can happen easily with incandescent enlargers.

The versalab tool is an excellent way to solve your alignment problem. I hope this link can help you.
Henry.

http://www.versalab.com/server/photo/products/parallel.htm

A simple quick check and inexpensive as well would be to place a level on the baseboard and a line level or small bubble level on the film holder and lensboard. If all match you should be lined up. Stopping down does help, also you may be getting a "pop" in the film due to heat from the enlarger bulb. Unless it was damaged I don't think the age of the lens should matter. I have been using 30+ year old enlarger lenses with no problems.

http://www.jeffreyglasser.com/

I bought a 3-beam torpedo laser level (as would be used in construction). Put it on the baseboard with a beam going up into the enlarger. The lens isn't necessary, but it should work fine either way if it's focused. I put a mirror aimed down in place of the negative carrier. Raise the enlarger head to a height to magnify error. The laser beam should reflect back to it's source. As you go out of alignment, it will aim to the side.

The alignment will probably show more on a 50mm than a 75-80, as there is more perspective distortion from the wider angle of view.

You do have depth of field like a normal lens, but not with bokeh and such. You're making a photo of film grain rather than a 3d scene.

To see if the problem is in the lens turn the lensboard 180 deg and see if the problem switches sides. If it doesn't the alignment is off. If it does the lens or lensboard mounting is bad.

I myself have encounterd in the past an El-Nikkor lens with unacceptable picture quality.
This was easily observed with testing against other lenses in the same enlarger with a known sharp negative.
Maybe someone had just dropped the lens on the floor.e

At 16x20 you should have no problems with a Nikor 50mm f/2.8 lens.

Bigger than that and it's time to look at APO lenses.

I have a really nice Rodenstock 80mm Rodagon lens that I use for 6x6. The other day I was in the darkroom for the first time in a couple of months, and printed a particular 6x6 negative to 13" square on 16x20 paper. Just because I felt like it I put my 90mm Omegaron lens in its place (supposedly an inferior lens), raised the enlarger head up a little to get the same perspective, made a second print, and I'll be damned if I can tell a difference.

As long as you stay within 16X enlargement factor, a standard Nikor 50mm lens should be within its design limits and perform fine. Would an APO lens be better? You can probably measure it, and a super trained eye might see it, but for the most part, unless you have a side by side comparison, the Nikor will be just fine. But an enlarger out of alignment - now that is something that can be spotted pretty quickly, especially if you print something that's sharp from edge to edge.

I read from very experienced users that the Nikkor could be an extremely fine enlarging lens but you'd have to find a good one because many of them have this problem.
So, yes, might very well be your lens.

16x20 is pretty big for a 35mm enlargement. Besides alignment, and stopping down, I'd check the negative with a good focusing aide on all corners. Make sure the focusing finder is correctly adjusted before putting it under the enlarger. I use a peak/micromega 1 with the huge mirror, it's so easy to check corners.

16 x 20 is pushing it with that lens. The field curves in the opposite direction of the film (assuming you are not using a glass carrier). To focus it (after you align your enlarger) you would focus on the center then move the column to focus on the corners. Set the enlarger column to the linear middle point between the two. You can stop down to f11 or f16. I have made 16x20 with that lens in that manner.