What is the best quality enlarging f stop? I have been told it is f4 and not as with camera lenses f8.

I have found that at f5.6 images are better than at f16 by a long way but I think you would have to have your enlarger well aligned to try f4 for big prints.

-- Mr. David A. Henderson (four.bananas@lineone.net), January 07, 2000

Answers

The optimum aperture is usually two or three stops down from maximum.

-- John Hicks (jbh@magicnet.net), January 08, 2000.

Try the various apertures and see.

What is right for one lens may not be for another. The same for camera lenses.

It may even vary within a brand and model.

-- Terry Carraway (TCarraway@compuserve.com), January 10, 2000.

I have found that in my Durst C35 enlarger the best results are attained with the f lens at 5.6,which, on the other hand, gives you enough exposure time to try proofs,I agree that this may change from brand to brand and from model to model.

-- Dr. Luis Felipe Escarza (lescarza@mail.ssa.gob.mx), January 13, 2000.

Hi,

You may like to get a copy of Ctein's Post Exposure. It's got quite a comprehensive enlarger lens test which includes the optimum f-stop of the various makes.

A lot of other invaluable info too.

cheers.

-- Y.K. Loh (ywkhiang@hotmail.com), January 17, 2000.

MTF tests by Schneider and Rodenstock generally indicate f/8 for their f/2.8 lenses and f/ll for their f/5.6 lenses.

-- Brian Hinther (BrianH@sd314.k12.id.us), January 25, 2000.

I have determined the best aperture of my enlarger lenses visually by examining the projected image of a test resolution slide from Four Seasons with a Peak grain magnifier. I tested the resolution in the central 2/3 area of the image and at various magnifications with a Leitz Focomat 1C enlarger. The Peak magnifier could not determine the resolution accurately beyond the central 2/3 area. As I stopped the lens down, the affect of diffraction was very evident. My conclusions are that the Leica 50mm f4.5 Focotar-2 lens displayed the best perfomance at f5.6, and diffraction definitely reduced resolution at f8 and beyond. For instance, resolution was at the optimum in the central region at f4.5, but slight color fringing and flare (vignetting too probably) would reduce the quality of enlargements at this aperture. At f5.6 resolution evened out at over 240 l/mm across the central 2/3 of the image, and the slight color fringing and flare visible at f4.5 disappeared altogether. Superb performance! With the 40mm f2.8 Focotar lens, f5.6 was also the optimum aperture in the central 2/3 of the image, but astigmatism came under control at f8, so this aperture is probably the optimum for this lens. For the older 60mm and 100 lenses for the Leitz Focomat II C enlarger, f8 and f11 respectivally, appeared to be the optimum apertures. The proof is in the pudding, however, and the best test is to make prints at the various apertures at different magnifications and compare them. My experience is that the phenominal resolution of modern enlarging lenses at f5.6-8 will not be fully utilized in prints less the 11X magnification, and that the flatness of field, uniform light distribution, and contrast will be more important for most purposes. I have also tested the 50 f2.8 Nikor and Componon lenses, and found that their resolution at f5.6 was equal to the Focotar-2, but that they exhibited slight color fringing and flare. This was not true of the older 50mm f2.8 El Nikor, which showed similar performance to that of the Focotar-2. The Focotar-2 beat it out in terms of resolution, but just slightly.

-- Eilert Anders (eilert@dav.com), February 16, 2000.