Please dig out an old Ansel book that talks about the difference between coated and uncoated lenses. (With illustrations) Read your Kingslake. This is a fundamental part of Photography that has slipped out of community wisdom because the folks who dealt with it and knew it are at least 55 years old, and the newcomers simply haven't dealt with it.
1. The number of air-glass surfaces, of ANY era, reduce the amount of light that is transmitted to the film.
2. Some classic lens designs were meant to limit that loss.
3. Some designs have higher natural contrast.
In the old days, you might choose a Zeiss Protar, or Goerz Dagor, as an all around lens. Wide coverage, and moderate contrast, and 4 air-glass surface, it was a safe choice for folks working in flare prone conditions.
The Tessar, having higher natural contrast than a Protar, was a great choice for folks who needed to shoot in flat lighting. But with 6 air-glass surfaces, the deep shadows were often lighter than anticipated. Why ?
Flare (or light that is not transmitted through a lens, but reflected within the lens) affects the shadows, and not the highlights. You have a harder time separating Zone I from Zone II because FLARE functions as fill flash, or base fog, (otherwise known as non-image density).
In similar conditions which cause an uncoated Tessar to image a foggy Zone I, a Protar will image a clean Zone I.
On your negative
Zone O: 0 exposure units
Zone I: 1
Zone II: 2
Zone III: 4
Zone IV: 8
Zone V: 16
Zone VI: 32
Zone VII: 64
Zone VIII: 128
A lens with a small amount of flare might add 1 exposure unit to the film. It raises Zone 0 to Zone I, Zone I to Zone II, and Zone II almost to Zone III. You lose your pure black, your threshold black, and fine shadow detail become murky and empty... unless you account for it.
But 1 exposure unit does not affect Zone IV at all.
Some classic lenses could not be used in all conditions. The classic Plasmat, with its 8 air-glass surfaces would give accurate midtones and highlights, but unless very carefully controlled, gave soft shadows because the flare inherent to the design provided built-in pre-exposure in the form flare.
This flaw, however, encouraged an aesthetic of soft, gravure-like, glowing blacks in the '20s and '30s. The Plasmat is the design which later became the Symmar, and the most common commercial design after WW2. Not at all, in its mulicoated form today, conducive for glowing shadows !
Some classic designs, like the Planar, had 10 or more air-glass surfaces and regardless of their high speed, were flare prone and impossible to shoot at all in many settings. After WW2, and lens coating was not a military secret, PLanar type lenses became the standard for small and medium format lenses,and fast view lenses.
Coating also made possible advanced wide field lenses, like the Biogon or Super Angulon, whose 8 or more air-glass surfaces were completely dependent upon coating to make them practical.
As lens coating became 'the thing' after the war, many photographers had their old lenses coated, and there were surprises sometimes. In a letter to Ansel Adams in the early 1950s, Paul Strand ruefully described the effect of having his trusty Dagor coated. It seems the delicate shadows of Strand' negatives was destroyed by the coating. The lens had become harsh, and hard... and Strand had to cope with a pure black Zone I. Adams and Strand coped with this 'improvement' by changing how they exposed and developed film. Just like us !
As late as the 1980s, commercial shooters took advantage of lens designs to support their work. Coated Artars and Symmars were relied upon in the studio and in carefully controlled settings, but Tessars ( Commercial Ektars ) were still relied on to give the most contrast on a sheet of film. Even coated, a Tessar still rendered cleaner blacks.
When Multicoating technology finally permeated the large format world, in the 1980's, the issue of variable lens contrast was pretty much resolved. There were differences to be sure, but one could go about their business without having to take lens contrast into consideration.
In my own work, I bought a brand new 8x10 lens over the winter, replacing my well loved Protar. As I near 60, I'm not able to focus as easily as I used to. I dislike darkcloths in the studio, and it had become too hard to focus the old lens. The new, multi coated lens does the trick.
Of course, I had to completely change how I exposed and developed film, but change is just part of life.
Please excuse any errors in this post to late nights in the darkroom, and too much coffee in the morning. PLEASE don't take my word on any of this, but check Adams, or, even better, Kingslake's, "History of the Photographic Lens" or, the Bible, "View Camera Technique" by Leslie Stroebel.
