Max resolution film size for large format.

[DREW WILEY]

There are photographers who deliberately used diffraction esthetically, for a softer-edged feel. For example, Meyerowitz routinely stopped down to f/90 in many of his shots. The effect was evident not only in 30X40 enlargements, but even subtly in 8x10 contact prints. His lens choices included a 10 inch Commercial Ektar and later a 250/6.7 Fuji W, I believe, which are both very sharp in normal usage - so this had nothing to do with a "soft focus lens" look; it was rather about nuance.

We should all feel free to make up our own rules, based on our own objectives and expectation. Perceived sharpness or deliberate modification thereof is just another tool in a potentially very large toolbox.

 

[Dan Fromm]

Back then lenses were uncoated, so you needed to stop down more than today.

Stuff and nonsense.

 

[Harry Callahan]

Uh-huh.

 

[Dan Fromm]

Uh-huh.

OK. Please explain why uncoated lenses need to be stopped well down. Be aware that I have several pre-WW I Tessars that shoot well near wide open. They are not coated.

 

[Harry Callahan]

Ok. If a lens is uncoated it does produce more flare than a coated lens. If you want to avoid low contrast you need to stop down the uncoated lens more than the coated lens. The OP was asking about enlarging negatives bigger than 4x5 - to (very) big prints. The bigger you enlarge a negative of a certain format, the less contrasty the print will be - and the more it matters that the enlarging lens does produce good contrast, resp. low flare.
In addition to that you cannot put as much uncoated elements into a lens than coated ones. If the elements are uncoated you can put three, maybe four groups into a lens but not more - because otherwise contrast would get too low. That`s why the Tessar lens has been invented as it has four elements, but in three groups - producing more sharpness than a triplet but about the same flare as a triplet. A modern, coated, six element lens should outperform a Tessar, even if the Tessar already is coated.
This means, an uncoated enlarging lens cannot produce as much sharpness at the same f-stop than a modern lens, so you again have to stop it down more.
Then, a hundret years ago, (most?) lenses weren`t corrected for curvature of field, so if you set the aperture to just that f-stop where the lens no longer has too weak contrast and too low sharpness - you can set sharpness on the middle of your print, but at the edges the print will be less sharp because plane of sharpness is bend.
Even with a modern lens, corrected for curvature of field plane of sharpness ain`t really flat - but less bend than on uncorrected lenses. So, again, and for the third reason you have to stop down the uncoated lens more than a modern, coated six element lens to also compensate for that.
Then you may end up at an f-stop which indeed could reduce sharpness of your print due to diffraction.

 

[reddesert]

Stopping down a lens sometimes decreases flare caused by ghost images, but it is not guaranteed to decrease flare caused by non-image-forming light bouncing off uncoated surfaces.

Lenses have been corrected for field curvature since probably the Rapid Rectilinear (1866), certainly the Cooke triplet (1893) and Tessar (1902) are corrected for field curvature. https://en.wikipedia.org/wiki/Cooke_triplet That doesn't mean field curvature is exactly zero, but that the lens is usable at a fairly fast aperture. Lenses have been usable at fairly fast apertures for more than 100 years.

Roughly speaking (for example for a normal lens for each format), the f-number required for a given depth of field goes up linearly with the format size, and the diffraction goes up linearly with the f-number. For example, if you use a 42mm lens on 35mm, 150mm lens on 4x5, and 300mm lens on 8x10, you get about the same DOF with f/5.6, f/20, and f/40 respectively. And if diffraction was the only issue, then those would yield about equal output quality when enlarged to the same final print size.

The problem is, of course, that diffraction isn't the only issue. Getting maximum quality out of the 35mm negative at f/5.6 requires more care to film-lens alignment, grain size, lens resolution, blah blah blah - I mean 35mm makes great prints, but nobody realistically thinks you can make it look like 4x5 just by buying an expensive lens. And there are probably plenty of people whose technique and subject matter allow them to use an 8x10 camera without stopping down to f/64 or even f/40. But again there are other issues besides diffraction that limit making a large print from 8x10", like your printing technique. It's useful to understand diffraction, but there are typically also more important things to worry about, to say nothing of artistic vision.

 

[Harry Callahan]

One problem with uncoated elements is that they do reflect light between each other. If the aperture on a Cooke triplet is wide open, the last element can reflect (non-image-forming) light to the middle element, which again can reflect this light onto the film or printing paper. The more the aperture is closed, the less light can be reflected between these elements, so contrast of the negative or print should increase.
Ok, then correction for curvature of field started (way) earlier than i assumed, but question is how good you could correct curvature of field on a 1893 Cooke triplet and how well you can correct on a modern, coated, six element enlarging lens. I have some projection lenses for 16mm film, coated Taylor Hobsons from the 1950s or 60s and they still suffer curvature of field. I cannot get the entire picture sharp, either the middle or the edges are blurred (to some extend).
Lens quality also does depend on how precise each element is ground and i think they couldn`t do this as precise a hundred years ago as they can today.
So an old enlarging lens still should suffer more curvature of field, even if corrected for, forcing you to stop down more than on a modern lens.

I was wondering where the statement the OP heard *could* be coming from - and a hundred years ago lenses weren`t as good as today. Yes there were Tessars - and i don`t think that you would run into diffraction-problems with an uncoated Tessar - but Tessars were rather premium lenses and i was wondering about "average" lenses for average photographers, because of which i was talking about a triplet before.

 

[koraks]

The more the aperture is closed, the less light can be reflected between these elements, so contrast of the negative or print should increase.

Uhm, no. The exposure will have to be proportionally longer, and proportionally nothing changes in the ratio between internal reflections within the lens and the image-forming, direct exposure. So no, stopping down doesn't help overcome flare issues of uncoated lenses. @Dan Fromm is right.

 

[DREW WILEY]

Too many incorrect stereotypes. The tessar formula has only six glass/air interfaces; another early formula, the dagor double triplet design, has only four. And both continued into the era of multicoating. My 14 inch multicoated Kern Dagor had higher contrast than any other lens of any camera size I've ever used. Too much contrast in fact for typical color chrome usage, so I replaced it with the previous single coated version for my 8X10 kit. The apogee of the tessar formula for LF usage is the Nikon M series, all multicoated. But if you want to go clear back into the 19th to make comparisons, that probably has little relation to any of this discussion with a very few exceptions. Might as well be shooting blue-sensitive plates as well, which contributed their own atmospheric look, probably even more so than lens flare.