While not completely convinced (or unconvinced) of the full impact of aperture shape, I'd note that, according to Christopher's theory, all lenses would have that lovely bokeh when shot wide open (an inherently circular aperture), which is where many of us would be looking to capture that effect.
And an observation that, especially under the subject line of this thread, many of us work in lf as much for the "mojo" of the large negative or contact print as for the pure numerically-defined resolution.
"Mark: "Yumminess" would indeed describe the kind of look I am after! I too have noticed that some older lenses drive more detail into the shadows and these lenses often also generate a light haloing around highlights, especially with B&W. Perhaps it is just a simple matter of less coatings and more residual flare per Ben's comment?" - Jack Flesher
Jack- I think the flare in uncoated optics just soften the grey tones (not the resolution) so the tones just "flow" from one to another. Modern multicoated optics seem a little choppy in the transitions, though it may just be my processing is a bit harsh. But (btw), my single-coated Acuton/Caltar-S 215mm behaves contrast-wise and mojo-wise almost exactly like my uncoated 210mm Dagor, and has substantially better resolution at the corners of an 8x10, so it ends up being my preferred lens in that focal length.
The halos around the highlights are more likely aberations, which I sometimes hate and other times am quite fond of.
I think Chris is testing lenses fairly conservatively - well within their intended use limits - and that this is why the aperture shape comes to dominate. If you stick to repro ratios and stops where aberrations are fairly well controlled, aperture shape is the only factor left.
In LF it is hard to find the consumer coke bottles that are everywhere in 35 mm and digital. I have a $100 wide-range zoom for my Pentax 35 mm that goes really funky wide open in 'macro' mode, where it becomes a swirly explosion of coma and aperture vignetting. Regular LF lenses don't get made like that, especially if you stick to normal taking distances, so for real mojo you have to go looking for portrait lenses or bottom feeding with budget projector lenses - just to get enough aberrations to get started.
I am not an optical engineer, but I used to be bombarded with trade rags after I once bought some laser optics in an unguarded moment. My impression was that for most 'normal' lens applications the real technical advances have been in production engineering. Good consistent glass blanks, computer-controlled polishing, CNC machining of lens mounts, more reliable cements and potting compounds. 'Better' can easily mean that a lens reaches a typical design spec at a lower price, rather than simply having more lp/mm.
"'Better' can easily mean that a lens reaches a typical design spec at a lower price, rather than simply having more lp/mm."
i think this is part of what's going on.
when i asked an optical engineer about it, his first question was "better how?" ... pointing out that my idea of better, which was more sharpness across the image circle, was just one of many things their customers wanted. among others were things that matter little to me, like higher speed, better performance at high magnifications, and lighter weight--all of which are major design parameters that require compromises to achieve.
he said that they have the technology to improve any and all of these things, but not often at prices the market will bear. the lenses available today represent a very mature technology, and any improvements are already pushing diminishing returns. to make a lens that's 5% sharper off axis, without compromising anything else, might cost five times as much money--an amount no one is likely to pay.
[from paulr re: Christopher Perez]...
Your conclusions about bokeh in LF lenses still seems to be based mostly on conjecture.
...
Hmm. So? Please define "bokeh". Technical dueling aside, IMO, "bokeh" is as much a personal response as a technical fact. Everybody's "je ne sais quoi" is arguably different. Until you can quantify bokeh, all you can do is hypothesize how its arrived at, and for each photographer, what it is, and how its achieved, is not a constant. A variety of photogs looking at a series of images would not necessarily come to the same conclusions as which photo exhibited the "best" bokeh, tho many may agree on a tight grouping of them. Within that group, there may very well be a variety of technical reasons why its "optimum". You are trying to quantify an intellectual continuum. As a methodology, conjecture likely has as much validity as rigor.
I think the formula you are looking for goes like this: {SUM(Chutzpah)+!MOJO}=bokeh/(n+1) where n+1 equals the number of lenses in your collection, plus the one you wish you had...
Re: " Your conclusions about bokeh in LF lenses still seems to be based mostly on conjecture. "
[pault responding to Christpther Perez]
In response to Paul Coppin's response to paulr's response above to Christopher's Perez response to the post: :-)
The claim from Christopher with which I disagree here and elsewhere, is that only the shape of the aperture of a lens contributes to _any_ difference in the out of focus area. While arguing "best" is subjective, I would think "difference" is much more obejctive. I don't think paulr is arguing "best".
My claim thru my own rather limited experience - and I am no optical expert - is that different lenses render the out of focus area differently in terms of resolution, contrast, flare control, color rendition, etc. all of which go into the making of bokeh. Whether such bokeh is pleasing or not is not in question. The question is whether there is _any_ difference.
"The question is whether there is _any_ difference."
exactly. i'm not looking for a formula that i don't understand. and i think it's great that Christopher took the time to do these comparisons, and to share the results with us--i'm not questioning that either.
i'm being critical of sweeping generalization that are stated as fact, even though they're based on one person's subjective look at a few samples under limited conditions.
"I think it's great that Christopher took the time to do these comparisons, and to share the results with us--i'm not questioning that either. "
I hasten to join you and add that I too appreciate Christopher's effort very much. If not for anything else, at least it leads me to pay more attention to certain aspects of my own image making. Thank you Christopher, and please carry on with your research.
As a person who makes a living in the highly technical engineering side of photography (yes Virginia, I am a rocket scientist) my heart is 180 degrees out from there. It's the romantic aspect of unquantifiable fuzziness where I'm at my peak enjoyment. Call it a magic bullet if you like. I hope no one is ever successful at defining the exact qualities. It will spoil the fun for at least one hopeless romantic.
Notice: Ebay is broke for me until I figure out how to change my e-mail password. That means you all have a fighting chance at those petzval's for the next couple of days. I can't place a bid!!
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