Optimal aperture when enlarging

I'm not that obsessive about sharpness, but I rarely print wide open nor stopped down to f/16 or 22. I during the first print from a negative, I check to see overall sharpness in fine detail and grain on the paper, but that's it.

Probably depends on a lot of factors, especially the negative, but I normally use f8 w/ my current enlarger.

My preface is F8 to 11.

momus said:

Probably depends on a lot of factors, especially the negative, but I normally use f8 w/ my current enlarger.

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I don't think the negative has much to do with it, rather the lens. Unless you're dealing with negative pop, but even then a small aperture won't save you. Some lenses are tack sharp wide-open, most a few stops down. It is simple to check with a grain focuser at the working aperture. Of course, alignment is a big factor too.

The size/format of the negative does matter, but the rule of thumb of "two stops down from wide open" is generally useful.
If you have a really high end lens designed for larger prints, wide open may actually be the best.
Diffraction kicks in at smaller apertures, but may not be very important for small prints.

Enlarging lenses, unlike the typical camera lens, are optimized for good performance within a certain magnification range, which the lens manufacturer states in the specs. And they are better 'flat field corrected' than the average camera lens. Rodenstock mentions that image defects occur when lens is wide open, so that should be used mainly for focus, as stopping down from wide open benefits Edge performance considerably and improves upon evenness of light distribution across the field from center to edge.
Rodenstock APO lenses are suggested for -1 f/stop, and 'lesser' quality lenses are suggesed for -2 f/stop. This not only reduces light transmission falloff toward the edges but also reducs 'image defects seen wide open. Rodenstock state that a lens generally should NOT be shopped down -3 f/stop. 'Beginner' 3-element lenses may improve in edge defects even with 4 f/stops. But Rodenstock notes that beyond 2 f/stops, diffraction loss gets large..

The preceding information extracted from Rodenstock enlarging lens iinformation aimed specifically to someone choosing a lens to be used for enlargement for Film Copy..

Paul Howell said:

My preface is F8 to 11.

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MattKing said:

The size/format of the negative does matter, but the rule of thumb of "two stops down from wide open" is generally useful.
If you have a really high end lens designed for larger prints, wide open may actually be the best.
Diffraction kicks in at smaller apertures, but may not be very important for small prints.

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wiltw said:

Enlarging lenses, unlike the typical camera lens, are optimized for good performance within a certain magnification range, when the lens manufacturer states in the specs. And they are better 'flat field corrected' than the average camera lens. Rodenstock mentions that image defects occur when lens is wide open, so that should be used mainly for focus, as stopping down from wide open benefits Edge performance considerably.
APO lenses are suggested for -1 f/stop, and 'lesser' quality lenses are suggesed for -2 f/stop. This not only reduces light transmission falloff toward the edges but also reducs 'image defects seen wide open. Rodenstock state that a lens generally should NOT be shopped down -3 f/stop. Cheap 3-element lenses may improve in edge defects even with 4 f/stops. But Rodenstock notes that beyond 2 f/stops, diffraction loss gets large..

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As a rule of thumb two or more stops down from full open and the sweet spot for most lenses is f/8 to f/11. The smaller apertures than those can start to have diffraction creeping in.

Two stops down, carefully aligned enlarger and glass negative carrier and you will get about the best performance from both your enlarger and lens! I use (prefer) Nikon enlarging lenses because I did side-by-side comparisons (same negative and setup) with Schneider and Rodenstock six-element lenses and preferred the Nikon results but the truth is that I don't think there was any "real" difference... just a combination of contrast and out-of-focus renderings. With a glass negative carrier and a properly aligned enlarger you can get great results from any decent lens.
Joel

I print mostly 8x10 and 4x5 from 35mm negative. I often use the 50mm f/2.8 at f/8 for the 8x10 and the 80mm f/5.6 at f/11 for the 4x5.

two stops down from wide open.

Enlarging lenses vary widely. Some cheap models need to be stopped down until diffraction limits sharpness. The several El-Nikkor 50mm f/2.8 lenses I used over many decades needed to be stopped down to f/4 to eliminate slightly uneven illumination. They were still sharp at f/5.6, but diffraction crept in by f/8 when enlarging fine grain negatives. Sometimes what at first appears to be poor wide aperture performance is really enlarger misalignment.

Jim Jones said:

Enlarging lenses vary widely. Some cheap models need to be stopped down until diffraction limits sharpness. The several El-Nikkor 50mm f/2.8 lenses I used over many decades needed to be stopped down to f/4 to eliminate slightly uneven illumination. They were still sharp at f/5.6, but diffraction crept in by f/8 when enlarging fine grain negatives. Sometimes what at first appears to be poor wide aperture performance is really enlarger misalignment.

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I've had good luck with El-Nikkor and Rodenstock lenses. You will get sharper images with a cheaper lens with an enlarger that is aligned than with a mis-aligned enlarger with an expensive lens. Enlarger lenses are so cheap now on Ebay. There seems to be a glut of 50mm enlargers. Most could be had for around $20.

I really believe the correct answer is "test it yourself". Sample variations, enlarger alignment, print size and magnification, all come into play.

This is something you can see just by sticking a grain focuser under the negative and looking at the grain as you change f stop. It start mushy, sharpens up, and then becomes mushy again. Unless you have something like the 45mm f4 APO Componon, which starts sharp, and eventually goes mushy, probably due to starting with a less ambitious aperture. Thats the secret to the APO bit....they just dont allow f2.8

However, physics can answer this, from a diffraction perspective, where destructive interference of light calculations can be calculated, by considering geometry and wavelength. You get total destructive interference when the distance travelled between one light ray and another is equal to half a wavelength. This leads to some algebra which tells you for a given wavelength, what the aperture can be.

If the negative has say 80lpm on it, then thats the limit the enlarging lens can see, as there is no more image detail than 80lpmm. Even if the enlarging lens is capable of 500lpmm, if there is no more detail than 80lpmm, thats all you are going to get down on the paper. At f11, the Rayleigh diffraction limited resolution is 136lpmm. This means there is no contrast for 136lpmm. So contrast should still be good for detail at 80lpmm. Contrast at 80lpmm on the film will be low, anyway, as thats approaching the limit of what a taking lens can record. If you were to consider the same arguments for 40lpmm instead, then f22 would be ok. 80lpmm will allow a 10x print to have 8lpmm on the print, which is practically perfect.

So for 10x enlargement, f11 is still fine. Really, adjustment of f stop enables setting of printing times.