Z Lenes Offer Less Character Than F Mount Lenses ?

Started 4 months ago | Discussions thread
anotherMike Forum Pro • Posts: 11,214
Re: A rant on aberrations, the photography community & lens manufacturers
28

saltydogstudios wrote:

I do think modern lens manufacturers design lenses that will test well. And those tests tend to be lines per inch charts mounted flat on a wall, resistance to flaring, and just a couple of other things.

Actually, not quite. Lens designers aren't using DXO or imatest to measure their lenses on a test chart and then gaming the design to do better with them. At least not Nikon. Most all modern lens design software allows for the designer to see the theoretical MTF performance of their lens during the design stage (so they can see what's going on with each iteration of the design), and most of the major players (Nikon, Canon, Zeiss, etc) have software that also simulates bokeh and other aspects (in Nikons world, it's the Optia system). And this actually ties into my rant - something I've been talking about for probably 3-4 years now regularly in the forums. And it ties in to one of your wishes, although in a different way.

As for Nikon, since I know this line the best, I can almost assure you that they are NOT always chasing "max test chart sharpness", and any reading of lens designers writings or interviews tend to show that. Like most designers, they have a vision for the lens, and they will try and design to that vision. It's why two excellent Nikon Z lenses - the 50/1.2S and the 85/1.2S, are different in terms of performance in portrait range. Two different designers, two different goal sets, but both high performing. The trickier question would be how a test chart could tell you that - and in some ways, it can't.

Education and awareness that lens performance - or rather, the evaluation of lens performance, is VASTLY more complex than an MTF50 score on a test chart, or a DXO grade, or even just a test chart at a fixed distance. It's not to say those things aren't useful - they can be, but they are a long, long way from adequately (IMO) and completely describing a lenses performance envelope.

The problem is, people want simple and they want easy. So the popularity of nonsense like the "10 sharpest (whatever focal length) lenses" youtube videos, or the obsession with scores and test charts. Most often these are used to provide "ammunition" for ones own purchase being better than someone elses purchase - brand defense, and that's pretty sad.

Let's take a sidetrip on aberrations for a second. You've got the common ones, and I think people definitely need to learn/understand the general impact of them: as in, things like field curvature and astigmatism really never go away as you stop down, which disproves the myth that all lenses are equal at F/8. But at the same time, aberration's go far deeper - there are various "orders" of them - commonly (IIRC) third and fifth are usually considered in the design. The correction for one aberration might be done by balancing it against another aberration. So it gets mighty deep mighty quick. See my comment about people wanting quick and easy again.

This leads to compromises. It may be on size / weight / price, or it may be character.

"Character" is not a compromise they make.

I own enough lenses - and not enough about aberrations - to know that I own two lenses (Leica Summicron, Fuji-X 80mm Macro) that are stunning for stuff like product photography - the objects have a 3-dimensionality to them that's astounding. These lenses are horrible for portraits for this reason.

We'll get to this in a bit when I delve into my current thinking on this.

Is that microcontrast? Half the photography community can't agree whether or not it exists.

The problem with the term "microcontrast" is that the photographic community bastardized the word. The ONLY scientific definition I've ever seen of it came from the late Hubert Nasse of Zeiss, yet SO many photographers bandy this term about with some usually undefined definition. It's like people in the world have a different definition for what the word "Truck" means - some folks say large vehicle that carries stuff, some say it's a feline animal with white whiskers, some say it's an exotic drink. Maddening. And it goes on - the folks who come up with stuff like "inter/intra tonal values" - sorry guys, a tone is a discrete value, and there is nothing within that. Maddeing again.

What I see often is that FAR too many people try to invent terminology either to make up for a lack of understanding of what's really going on (and I fully admit to having done so in the past) or do try and sound "important" and knowledgeable in a forum discussion. There's a guy who sadly still posts here who talks about "internal contrast" and "external contrast" and all this utter nonsense, while telling you he only works with "high dollar clients" like he's some sort of lens whisperer and super photographer, yet when you actually dig down into what is going on, you see he's utterly full of it. And there are many like him. Witness the guys in the adapted lens forum who still cling to the "less elements is better" theory. Or the scores of folks who talk about "deep natural color" of lenses (usually to defend "their" choice) when reality is quite different. Adding to this, and I'm going to p*ss some people off here - is a lot of forum photographers are older and male, and sadly, stubbornness, obstinate beliefs and bias are strong components of their personality, and all of that are serious detriments to trying to learn. But a lot of it is just that we, the community, aren't educated so we venture off into crazy subjective nonsense, which often leads to absurd absolute/universal statements (like "all modern lenses render flat") and it feeds. The BS multiplies. You have potentially good reviewers start to walk off into crazy land talking about low element count lenses and stuff.

A little field curvature in a portrait lens isn't a bad thing, but because the way everyone measures lenses with a flat test chart, they'll say the lens "isn't sharp in the corners" (a few reviewers know to focus in the corners for corner sharpness). A little spherical aberration isn't a bad thing, but maybe that will lead to less contrasty lines per inch so they remove it.

Depends on what you shoot. For some things a bit of field curvature, no problem. For others, huge problem. It's a matter of degree too. Interesting side note: a somewhat "famous" in the film era lens designer, Jun Hirakawa, wrote that (IiRC) in order to maintain proper dimensionality in an image, it was best to absolutely take pains to minimize astigmatism, even if it meant letting field curvature "go" a bit. (Note that astigmatism is the difference in field curvature essentially between sagittal and tangential orientations). My own belief is that the worst thing is WAVE curvature because in my studies and print tests, I've found the human eye/visual system likes consistency, and if you've got a scene with detail in a lot of spots, and your lens has wavy curvature, then performance is inconsistent. My current thinking is that the viewer would rather have consistent performance over an image with incredible "really good in one place" performance at the expense of consistent performance, at least on natural/honest landscape scenes.

If they photography community understood more about what aberrations are, and which are good or bad for what context, maybe the lens manufacturers would start optimizing for context instead of test charts.

It's not about understanding aberrations. It's about understanding how we should talk and think about lens performance in terms of resolution. This is what I've been harping on in the forums for a few years now.

I'm quickly running out of characters to post all of this, but in essence:

Think in terms of MTF resolution structures: I like to think of coarse/large structures (a good proxy for contrast, think 10lp/mm area or so), medium/fine strutucres (more fine detail, but not the finest detail, say, 30lp/mm or so), and very fine structures (50p/mm+). BETTER YET: Realize that there is no one singular resolution frequency that uniquely and totally defines "sharp" in every situation. Also think about how much high frequency detail one can achieve in real life vs what the lens/camera can do theoretically - my often used analogy is the street shooter, moving, moving subject, zone focusing, will never see high frequency detail, while the landscape shooter in clear atmosphere, serious tripod/head, good shot discipline, surely will -- and think about how important high frequency measurement is to the second, but not the first shooter.

Otto Schade, who pioneered MTF in the early days, found that image quality was determined by the square of the area UNDER an MTF trace where resolution frequency is plotted against contrast. This has pretty huge implications if you visualize it. Since there is more contrast at lower frequencies, that also illustrates the importance of the lower and mid frequencies; yet often photographers are only concerned with the highest numbers. Hubbert Nasse (again) took this further (you can read about this in either his 1st or 2nd MTF white paper from Zeiss, sorry, don't have the links handy) by saying it's ALSO important to have your lens perform in the region of frequencies most important to your subject. Going deep into the rabbit hole. Really deep, which gets us back to the "people want simple and easy" discussion.

My current thinking - and I say "current thinking" because even though I'm older and thus am suspect to biases, I try to stay educated and learn and not close off the mind - is thus:

The best lenses are very well balanced in terms of how they "treat" the frequency structures from coarse to very fine. Even more importantly, my current thinking is that once we get "past" bokeh and OOF transition and flare, it's the subtle differences in this balancing that generate subtle differences in rendering. Why a 50/1.2S, 85/1.8S, and 85/1.2S all are slightly different. And this balancing intersects with the sensor/resolution of the body. A lens well balanced only for film (lower requirement for very fine structures) won't perform so well on high rez digital for use cases where these structures can be realized.

The cinematography community seems more advanced here.

Cinematography has different needs, resolution wise, but yes, in general they are more aware of the differences and you see this in various lines - Zeiss master primes render differenty than signature primes. And if we go back to my "balanced" discussion in the previous paragraph, you'll see the Cine folks often talk about lenses that are sharp but still are natural - that's because the lens designers are very AWARE of this balancing. Nikons certainly are, even though they don't make cine lenses.

In the art vs science aspect of making lenses - the art being about choosing which aberrations to keep, the science being about optimizing to specific tests - we seem to have swung quite a ways towards science.

Not quite, science is there - there is no black magic in making lenses, no secret pixie dust. What we see today is lenses that are designed to mate well with the sensors/cameras of TODAY, not 20 years ago. The theoretical maximum image quality available to us today in a DSLR/SLR/ML sized camera is vastly better than in 1980. As such, to be able to extract that quality requires lenses that are designed with those sensors in mind. But at the same time, because of bias and also other aspects of psychology, some folks "expect" or perhaps "want" an older look, perhaps because even in the film era, they never experienced a better look. Myself, I used 35mm because I had to - broke, never was a rich guy, but I dreamed of 6x7 or 4x5 LF film quality, which I had used, and here we are, modern era, and we can get there. But to get there requires lenses designed in the modern era.

But the major manufacturers don't talk much about it, they just publish MTF charts for those who know how to read MTF charts.

Manufacturers MTF charts are quite limited. Better than nothing, but quite limited. But again, given most people can't even understand the implications of what the most basic manufacturers chart shows, how could we hope they would understand it if we had all of the necessary information.

As for the OP's question - I don't have enough experience with Z glass to comment, but the feeling certainly is that Nikon are optimizing towards "flawless but heavy and expensive lenses" - at least for certain lenses, in contrast to historically them keeping the 50mm f/1.2 - a beautifully flawed lens - in production complete with AI "ears" for decades. But I don't really know what they're thinking or what they're optimizing for.

Nikon is an optical company. They are striving for excellent performing glass. At the same time, having shot enough of various brands across the decades, I believe there *is* a Nikon "house philosophy" which is "do no harm, particularly with portraiture" which means some other brands will test on the chart slightly better, or another brand might be a better tool for a specific task.

End of my rant, sorry for the length

-m

ps: if you made it this far... education. Do what I did. It will take some time. Start with the aberrations article on opticallimits. Then read the Zeiss whitepapers on bokeh and MTF from Zeiss. Search for the writings about the Panavision (cine) Primo 70 lenses, where you'll run into Otto Schades theories. Wander through Warren E. Smiths "Modern optical engineering". I can't say I grasped everything there - my math skills are obviously suspect these days. Look at the blog discussions from Roger Cicala on lens rentals for a few years ago when he did MTF measurements. You'll get your education, and you'll find some interesting things. Like how, nobody, not even the author of a lens design course book, ever mentioned "low element count" or "deep natural color" or any of the nonsense paraded in forums. But it will take a lot of time, and again, most people don't want to take the effort. I'd say start with the aberrations article and the Zeiss white papers; and even the latter gets deep.

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