Just about to buy an enlarger lens to enlarge from 6x7 negs, and would appreciate some guidance on a particular issue.

My preference (as I am obsessive about image quality and optics) is to go for the Schneider APO-Componon 90mm. This is the closest to the appropriate focal length that exists in this lens range. However, I have also read that getting a longer lens (say 100 to 105mm) would be beneficial, because it would allow me to use only the area in the middle of the image circle, and hence get the most of the "sweet spot". For exmaple one posting on the web states that "lens performace suffers that far off axis as the MTF curves fall precipitously" even though they the lens would cover the image area. Now, there is no APO-Componon in this range, but there is a Componon-S.

I know that it is probably not necessary to get the APO, but I'd like to, as I am willing to spend more to get even small improvements in optical performance.

My question is: will I get better optical performance using the APO 90mm lens, or using a slightly longer non-APO lens, hence using the middle of the image circle. Or is there another lens range that would allow me to get APO optics at the right length (say 105mm)?

Many thanks in advance!

-- Ed Hurst (BullMoo@hotmail.com), April 23, 2001

Answers

I use a 80mm F5.6 El-nikkor for 6x7 and get sharp results to the corners on 16x20 prints. FWIW.

-- GenE Crumpler (nikonguy@att.net), April 23, 2001.

The right focal length for 6x7 is 90mm, there's absolutely no need to go longer. Any slight optical advantage you might get from using a 105mm lens could easily be negated by the increased enlarging distance, and subsequent sensitivity to vibration. In any case, apochromatic correction is of dubious benefit in B&W enlarging, where, at best, the paper is only sensitve to blue and green light.

-- Pete Andrews (p.l.andrews@bham.ac.uk), April 23, 2001.

Using a slightly longer lens than normal will give somewhat more even illumination and avoid the edge of the image circle where the MTF does fall off some. The longer lens will limit the maximum print size you can make. To get the performance that a top quality lens is capable of, be sure that your enlarger is aligned and use a glass carrier.

You might want to consider the 105 mm f4 Apo-Rodagon-N.

-- Michael Briggs (MichaelBriggs@EarthLink.net), April 23, 2001.

If you decide to go longer than 90mm, first make sure it will work with your particular enlarger. I found that I was not able to use a 105mm on a Beseler 67.

-- Tom Raymondson (rayson@pacific.net), April 23, 2001.

Hi, Ed. It seems you're worrying too much on lenses, otherwise you'd tell us some other important facts, such as: enlarger, it's head, your previewed magnification, etc. Some enlargers are so troubleful to align that you'll certainly find a good idea to use a longer lens so to avoid problems focusing the corners. If you can keep consistently perfect (or near so) alignment, you'll find that openning any lens to its better aperture can do wonders. On the other side, if light distribution isn't matched to a specific lens, you're in trouble again. Doing B&W prints, you'll hardly see any difference using APOs or any other 6 element lens, except on your pocket. And, as it seems to be fairly indulgent, I'd suggest him a 90mm Nikkor-Rodagon- Componon and a Zig-Align or Versalab device. Such a pair might work for you. Good luck.

Cesar B.

-- Cesar Barreto (cesarb@infolink.com.br), April 23, 2001.

Cesar,

You're right - I have been focusing largely on the lens (no pun intended)! So far, I have bought the enlarger, but have not set it up yet, as I am about to move house. So I have not yet encountered many of the issues you raise! For the record, the enlarger is a Durst M805 with colour head. My most common print size will be 10x8 inches, though I will intermittently do much bigger prints. Does this help?

By the way, you advise using a "Zig-Align or Versalab" - afraid I don't know what these are! Could you explain...?

Thanks for all help so far guys!

-- Ed Hurst (BullMoo@hotmail.com), April 24, 2001.

If you are only occasionally going above 8 by 10 inches then buying an APO lens is going well over the top. Any of the 6 element lenses from Nikon (my personal preference), Schneider or Rodenstock will do very well indeen. By the way the Durst 805 is a splendid enlarger. The zigalign is a device that (I believe) uses mirrors to help you see that the head, negative stage and baseboard all all parallel. See Ctein's Post Exposure for a full description. The money you save by not getting an APO lens will leave you enough over to buy the Zig Align and a good bottle of Scotch into the bargain.

Adrian

-- Adrian Twiss (avtwiss@ukonline.co.uk), April 30, 2001.

I've found the Dursts to hold alignment very well.

I use the Versalab Parallel laser alignment tool (www.versalab.com). It's a laser in a box that sits on the baseboard; the laser is reflected from the lens panel and neg carrier to judge/set alignment. It's somethign you do every now and then; if you check it regularly, the tool is so sensitive that you'll never do anything but adjust alignment.

The 90 APO-Componon should be fine for 6x7. I use an 80 Componon-S, usually at f8; it prints the grain sharply out in the corners and in the center, so I don't see any need for anything supposedly better.

You _must_ buy or build some sort of alignment tool of the sensitivity of the Parallel or Zig-Align; otherwise there's not much point in buying a lens better than an ordinary Beslar.

-- John Hicks (jbh@magicnet.net), April 30, 2001.