I need an enlarger lens for this 6X6 format. Maximum sharpness is what I seek. I've been told every focal length between 75 and 135mm. I also read about lenses particularly good for B&W that claim to have APO coatings that allow a certain spectrum of light that our eyes cannot see but becomes extra sharp with black and white papers.

I know the major brands Nikor, Schneider, Rodenstock but which one? I was unable to find MTF tests to really compare them. Maybe the experience from the group can make suggestions on focal length and sharpness. I have the Beseler 23c if that makes any difference.

Thanks in Advance, Joe jmlacy@flash.net

-- Joe Lacy (jmlacy@flash.net), July 21, 2000

Answers

http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=003WQx

-- Pat Raymore (patrick.f.raymore@kp.org), July 21, 2000.

If you are in the US, the US distributor for Rodenstock will mail you a brochure with the MTF curves of their enlarging lenses. HP Marketing at http://www.hpmarketingcorp.com/

Schneider provides these curves on their website: http://www.schneideroptics.com/enlarge/enlarge.htm

Nikon seems to provide only the most basic information such as mechanical dimensions and qualitative assertions of quality.

I would use extreme caution in reaching conclusions by comparing curves published by two different manufacturers. Too many minor details can influence the curves, such as whether the curves are calculated or measured on production lenses and also what spectrum of light was assumed. Even specifying "white" light might be insufficient to nail this down.

Having said that, the MTF curves can be very useful for comparing lenses offered by the same manufacturer, e.g., comparing their 4-element, 6-element and 6-element Apo lenses. Also, you can see how much the curves fall at the edges of the field. This natural decrease in quality is why some suggest buying a lens with a focal length slightly longer than the miniumum required. For 6x6, consider focal lengths from 80 to 105 mm.

Re Apo lenses: the question is whether the modest increase in quality is worth the increased cost. Since you say that you want the "maximum sharpness" (implicitly with no cost consideration), then you want the apo lens. The biggest difference in apochromatic lenses is probably the glass used, aiming for lower dispersion in high refractive index glass. The coating is really not the main issue, though one should expect multi-coating on a lens of this caliber.

If you seek maximum sharpness, be sure to check the alignment of your enlarger and don't stop the lens down more than a few stops. Ideally use a glass negative carrier to keep the negative flat. These steps are probably more important than the difference between a 6-element lens and an apo lens.

-- Michael Briggs (MichaelBriggs@earthlink.net), July 22, 2000.

In the book Post exposure - Advanced Techniques for the Photographic Printer by Ctein (focal press, 1997) you find a very good chapter about enlarging lenses and the results of a larg test (p 47 - 66).

-- dominik (sehen99@gmx.ch), July 22, 2000.

1. Keep in mind that the most expensive lenses (the HM apos, for instance) tend to be optimized for large size magnifications.

2. You cant go wrong with a Schneider Componon or an equivalent Rodagon.

3. In fact, Apo is less pertinent to B&W work, as paper emulsion is orthochromatic and not panchromatic. So you don't need correction at three separate spectral wavelengths, only two. That is a mid range lens should behave as well as an Apo lens.

4. Ctein's article is a good read.

5. Don't sweat it. Enlarger Alignment, vibration reduction, enlarger column rigidity will all contribute as much to sharpness or more than blowing big bucks on a top range lens.

6. If you can find one, a 60mm WA Componon is a good idea, because you can pull big prints without pushing the head all the way up.

-- Mani Sitaraman (bindumani@pacific.net.sg), July 26, 2000.