I've written about this before (this is stock lecture #173), but I thought I'd take another stab at trying to illustrate the difference between lens contrast and lens resolution. These are illustrations only—software analogies of what lenses with these properties might give you. But sometimes, for us visual people, it's simply easier to see what we're talking about than to—well, talk about it.
Lens with neither contrast nor resolution (soft focus lens)
Lens with good resolution but low contrast
Lens with good contrast but low resolution
Lens with both adequate contrast and adequate resolution
I had a little trouble here because reducing the JPEGs in size tended to mask the qualities I'm trying to illustrate. (Also because the file I chose turned out not to be critically in focus: SNAFU.) Here are a couple of details to make the last comparison a bit more clear:
Contrast without resolution
BothAny of these types of lenses can be pictorially useful. The so-called Pictorialists at the turn of the 20th century prized lenses that had low contrast and low resolution—they were the opposite of us—and eagerly sought out exemplars that had just the balance they sought. Some of them were quite fanatical about it, and argued about which lenses had just the perfect degree of unsharpness with the same vigor with which we pixel-peep today.
Pictorialist photograph by Clarence H. White, made with a lens that had
low contrast and low resolution. Note how it also masks misfocus!
(This Clarence White photograph was also printed with low contrast, but don't let that distract you. Not the same thing.)
When Eastman Kodak was developing its famous series of Commercial Ektar large format lenses (in the 1950s, I think), its scientists conducted a series of empirical tests—they showed a large number of prints to a large number of people to find out what technical properties people actually preferred the look of. They found that people liked high contrast but not-so-high resolution, so that's how they formulated the lenses. Commercial Ektars have a particular rich-but-smooth look that many large format photographers still prize today.
Here's a link to a photo taken by Peter Lerman with a Commercial Ektar—this might look like it has good resolution to you, but that's because it was taken with a 4x5-inch camera, preserving all the fine detail it does have. The lens actually has relatively low resolution. But very good contrast.
...Actually, thinking twice, that example might only confuse people, because it also has contrasty lighting, and that's not what we're talking about here. Lens contrast has nothing to do with subject brightness range or the overall contrast of the picture/print; it affects microcontrast, not overall contrast. Here's another example, a picture by Frank Petronio taken with a 14" Commercial Ektar (Frank's a TOP reader so I'll presume to post the picture here hoping he doesn't mind):
(Again, the impression of good resolution is a function of the original photograph being made from an 8x10" negative, and the democratizing effects of JPEG reduction.)
A B&W photographer for most of my life, I agree with Kodak's test subjects back in the '50s: I've always liked lenses that have better contrast than resolution.
Now, to some extent, these distinctions no longer matter. Lack of sharpness is just not a big problem with most of today's lenses, and of course various species of perceived "sharpness" can be selected in software after the fact of taking the picture. I've written about that before.
For the most part, I will say that I don't particularly care for either "sharp" or "high resolution" photographs. (It fits some pictures aesthetically, but other pictures it just doesn't, and, these days, more pictures are ruined by being too sharp than are ruined by being too soft.*) Oversharpening is not quite the epidemic it was a few years ago, but its relentless overuse has pushed our perception of "normal" way up the scale. Excessive "sharpness," especially excessive unsharp masking, can make me feel nauseous (really—it can be a visceral, physical reaction). You might be amused to learn that a fair number of "found" JPEGs that I post on this site I actually de-sharpen first! I personally prefer vivid pictures—and that often requires judicious sharpness that emphasizes analog lens contrast or its software-created equivalent. (It also concerns lighting and tone, but those are other posts.) As with most things in photography, it varies according to the needs of the particular photographer's style or the particular picture.
*For those of you who bought Ctein's $19.95 "big print," that's a very sharp picture, but one that I don't consider too sharp—the sharpness it has is appropriate to it aesthetically in my opinion.
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Original contents copyright 2012 by Michael C. Johnston and/or the bylined author. All Rights Reserved.
Featured Comment by Crabby Umbo: "As an aside, I think this was actually sort of a big deal in the old Leica/Contax rangefinder debates/wars in days of yore. I can't remember which or what, because my mind is shot, but I do remember that Contax rangefinder lovers were enamored of Carl Zeiss lenses and what they did, which was different than what Leica lenses did.
"Not to start a 's**t storm,' but, as a personal opinion only, I was never that hot on Leica lenses. People in the '60s always waxed poetic about the 'look' of Leica glass, but I never cared for it, and every time a photo mag ran an actual lines-per-millimeter/sharpness test, they were consistently beaten by almost any Nikon or Canon glass of the same focal length. Carl Zeiss glass, to me, always seemed to be a better balance of 'whatever' for my photographs. And in fact, I think pre multi-coating, you could make a lens really sharp, but not all that 'zippy,' or you could make a lens contrasty, but not all that sharp, it was sort of a see-saw effect, up on one side, down on the other. More elements, more sharpness, more surfaces, more light bouncing around and affecting contrast.
"The development of multiple coatings, and more exotic glass threw a lot of this stuff out the window and changed development of camera glass for the better.
"I'm also on the Commerical Ektar train, whatever it is with those lenses, they certainly had some sort of 'look' that was superior, but I'd certainly want a 14-inch in a modern shutter for less money that a used car, and then I'd be happy. Ditto for a screw-on-able filter adapter that was on the lens 'rock-solid.' All the times I've used a 14-inch, I think it's magical. But I can look back on my 4x5 stuff from shooting catalog in the early '70s, and I even have stuff shot on an uncoated Zeiss Tessar that looks drop dead great. So go figger...."
Mike replies: What you say about the "see-saw" effect was once very true, and now not nearly so much. Now, most lenses I see have very good contrast and very good resolution, although one of the two may be just a little more "very good" than the other.
Ctein adds: Well said, man, well said!
Today an awful lot of people (and review sites) confuse sharpness with resolution (not the same thing!) and confuse both with overall image quality. Many lines of evidence lead me to this conclusion:
1) The number of lens tests that report resolution numbers or MTF figures and very little else. Do I really need to elaborate on how many lens characteristics (and problems!) that misses?
2) The popularity of "sharpen for output" plug-ins. I've tried 'em. I've abandoned 'em. Truly, I can't figure out what they're good for. It always looks crappy when I use them. In fact, I do a hell of a lot less sharpening than most printers, and people don't complain about blurriness in my results. That's true for my printing for clients as well as my own, and for working on everything from six megapixel digicam files to 200 megapixel film scans. A little judicious sharpening early in the process—primarily deconvolution—yeah, I'll do that. With care and common sense. But slamming up those edges and turning them into haloed and crufty garbage because it makes the output look better? Not in my book.
3) The surprisingly large number of readers who just assumed that I was evaluating the zooms vs. primes on the basis of resolution/sharpness although the word resolution never appears, the word sharp(er) appears exactly twice and the word crisper only once, and that's across over a dozen comparisons. I don't blame the readers for that; it's what bunches of review sites out there are claiming is of paramount import, and they reasonably (if incorrectly) assume I'm gonna do the same thing.
I will point out that the kinds of extremes you talked about in your lens examples are somewhere between rare and nonexistent in modern lenses. [This is true. I was just trying to illustrate the ideas, so I overexaggerated the effects to make them obvious. —MJ] Designers do a much more balanced job, on the whole, of correcting their optics, and a lens that delivers extraordinary sharpness over its entire field, like the Olympus 45mm, is likely to be well designed in other respects. But there's no guarantee of that, and one has to look. In fact, that 45mm has very good microcontrast, which is not remotely the same thing as sharpness and resolution. That's one of the biggest reasons that it looks so much better than anything it's competing with.
Conversely, according to the resolution figures, the Olympus 12mm a great lens. When you look at how that fine detail gets smeared in the corners, it stops being great and merely becomes good. Oh, it's resolving, but it's butt-ugly resolution...
Here's a sample photo from the corner of a frame made with the Olympus 12mm lens. Note the high degree of enlargement, to insure the details show up well online. Clearly the lens is "sharp" down to the near-pixel level, which is reflected in its good MTF and resolution scores. But there's substantial smearing, which in this small section looks like camera shake or motion blur on the diagonal from lower left to upper right. It's not; the frame is rock steady.
This kind of defect is much more noticeable to the eye than a simple blur would be. It becomes especially obvious when there are areas of bright strong contrast, like foliage against sky or sunlight glinting off of leaves or water.
Good sharpness; not good image quality.
Some issues depend on workflow. I will assert that overall lens contrast and color rendition are not significant issues in digital printing. They're much more serious for darkroom printers. Similarly, distortion and chromatic aberration are readily and invisibly correctable in software (up to a point; the Olympus 12mm shows that bad things happen if you go too far). It's pretty well impossible to fix these in the darkroom. But important or not, they do exist as lens characteristics and they are only indirectly related to sharpness and resolution.