M9 diffraction limits

[mjh]

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It’s a complex issue involving several variables, and there are different questions commonly asked, each emphasizing some variables and de-emphasizing or ignoring others.

 

For example one can pitch diffraction against lens aberrations, wondering how much one can stop down to reduce unsharpness due to aberrations before sharpness deteriorates again due to diffraction. Framing the issue this way implies that one doesn’t care about depth of field, and one also neglects the question of whether a certain amount of unsharpness would be resolved by the sensor (or film for that matter) anyway.

 

Or one might want to maximize depth of field, wondering how much one can stop down before diffraction makes it shrink again, yielding a different answer. Asking this question presumes one doesn’t worry about lens aberrations, and again the issue of sensor resolution is ignored.

 

And then someone might worry how far he may stop down (for increasing depth of field or for other reasons) before the unsharpness due to diffraction would visibly show up in the digital image created by a sensor with a known pixel-pitch, disregarding lens aberrations.

 

Depending on the circumstances, one question may be more relevant than the others. And still, all these questions are equally valid.

[jaapv]

I don't think this informative article has been linked to yet:

 

Depth of field and diffraction

[lars_bergquist]

It’s a complex issue involving several variables, and there are different questions commonly asked, each emphasizing some variables and de-emphasizing or ignoring others.

 

For example one can pitch diffraction against lens aberrations, wondering how much one can stop down to reduce unsharpness due to aberrations before sharpness deteriorates again due to diffraction. Framing the issue this way implies that one doesn’t care about depth of field, and one also neglects the question of whether a certain amount of unsharpness would be resolved by the sensor (or film for that matter) anyway. [ ... ]

When analyzing a problem scientifically, we try to sort out the variables, and then we choose one to fiddle with and see what happens. No 'holistic' attempts to throw it all into one large pot have a chance to succeed. Just look at the majority of postings.

 

I do not ignore depth of field. I have expressly stated (in case you are interested) that d.o.f. is among the second-order consequences, but that I will not delve deeply into this becase it is a more basic aspect of the problem that I want to analyze. Depth of field is a different discussion. Most all problems or issues in photographic technique are to some extent interdependent, and if we were obliged to always discuss all aspects of everything simultaneously, a Babel din would be the only result.

 

'Ceteris paribus' is often a sound methodology, as long as we remember that it is just methodology and that 'out there', other things seldom stay equal. But by then, we should have a grip on the structure of the problem so that we have a sense of the causalities and proportions.

 

The fracted old man

[ianspector]

Now we have gone and fracted the Old Man. At the risk of causing him refraction I will make a few observations:

 

What an extraordinary amount of knowledge is amassed in this forum, and how generously it is given

A key lesson for me is to learn the physical characteristics of my equipment and their limitations in a controlled environment so that I do not have to worry about them in field (or in this case above the field) situations

It is a miracle that most of my shots were so sharp as my focussing consisted of turning the ring to infinity and hoping it was set up properly

The glare cause by sun through haze in the air compresses the histogram to the right whereas, as was pointed out earlier here, actually led to me going to f/8 in the first place; all the other shots at f/4 were better exposed

 

My final confession is that this was the first time I had moved the Noct off the f/1 setting so it was a pretty silly way to start understanding the interplay between diffraction, aberration, focus shift and depth of field.

 

Ian

[okram]

No, not at all. The only variable factors in the (approximate) formula for the Airy disk size are the wavelength (usually set to 555 nm or in other words green) and f/D where D is the diameter of the aperture. But since f/D is the relative aperture, the only factor is the relative aperture. At a given aperture value, the size of the Airy disc is constant, regardless of the focal length of the lens.

 

 

Again, the relevant factor is f/D. A larger format means longer lenses (f increases) and a larger diameter of the aperture (D increases). So in the fraction f/D, both numerator and denominator grow by the same factor, canceling each other out.

 

 

Fortunately the location of the nodal point is not a factor here, so we can safely ignore it.

 

 

No, it wouldn’t. White balance makes no difference. Now if you did set the color temperature to some really perverse value that was way off, then either red or blue would contribute much more to the image than it should and in such extreme cases it could, theoretically, make a difference. But that would be the least of your concerns then.

 

Green is the range of wavelengths both our eyes and the sensors of our cameras resolve best, so once we have made sure that diffraction won’t cause any problems in the green channel, there is no need to worry about red or blue.

 

 

Given a pixel pitch of 6.4 µm for the EOS 5D Mark II it would be prudent to stay below 2 x 6.4 / 1.35 which is approximately 9.5.

 

Thanks, I learned something.

[mjh]

When analyzing a problem scientifically, we try to sort out the variables, and then we choose one to fiddle with and see what happens. No 'holistic' attempts to throw it all into one large pot have a chance to succeed.

That’s what I was trying to say. There are different angles, each equally valid but each ignoring parts of the issue. Like the blind men and the elephant. Or one could try to attack the problem head on in all its complexity, but that is usually just not practical. So it’s OK to ponder just one part of it, as long as one keeps in mind that it represents just one angle on something more complex, and that it doesn’t invalidate other approaches.

[xtoph]

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[...] the general contrast of the lens can begin to drop slightly (a sign of having passed the diffraction limit) already at f:4, while a slightly slower lens may show this effect only from f:5.6, and an ancient lens maybe not at all within the available range of f-stops. Really old Leica lenses often have stops down to very small apertures, while current lenses normally put a stop to the game at 16. Now you know why.

 

i'm not sure i understand you here. i think you're saying that modern lenses are sometimes good enough to be diffraction limited (ie, nothing other than diffraction is holding back the the image quality at a given aperture) at larger apertures than was usual in the past, with older lenses. i think this is true, afaik. but you then make a sort of jump from there to suggest that this justifies not including smaller apertures such as f/22 on modern lenses. this part doesn't quite make sense; assuming both new and old lenses will be primarily limited by diffraction at, say, f/22, then the new lens will perform no worse than the old lenses did at that aperture (and possibly better, if the old lens was still insufficiently corrected). f/22 is as useful now as it ever was. of course, i don't mean to hold you responsible for modern lens design decisions, it is just that i wonder if i was understanding you correctly.

[lars_bergquist]

Well, you don't judge performance only in comparison with older lenses, you do also judge it in absolute terms. And the fact is that general contrast (as measured by the 5 and 10 lpm curves of the MTF graph) starts to drop slightly after 5.6 at the least, with modern lenses, and the fall-off will be perfectly visible at f:16.

 

As long as there are residual aberrations, they will continue to influence definition, but from 5.6 or even 4.0, diffraction will dominate. Even so, stopping down from 4 to 11 may often make the picture look overall 'sharper' because of increasing d.o.f. But micro-detail in the plane of best focus will implacably tell the truth.

 

Still, sharpness is not all there is to a memorable picture. Most iconic pictures are not very sharp, in fact! Sharpness is the fetish of boring photographers.

 

The aberrant old man

[RSL]

Sharpness is the fetish of boring photographers.

 

Ah ha! The truth always surfaces in the end. Thank you, Lars.

[ianspector]

"Sharpness is the fetish of boring photographers."

 

 

 

None taken,

 

Ian

[jaapv]

I'm happy to report I take plenty of non-boring photographs..

[SJP]

for the Dutch speakers "als iemand vertrekt is het logisch dat er een afscheidsreceptie komt maar als er een afscheidsreceptie is dan houdt dat niet in dat iemand vertrekt" mr. HAFMO van Mierlo bij zijn vertrek uit de politiek.

 

Loose translation "if someone decides to leave there is a farewell party, but if there is a farewell party this does not imply someone is leaving" from Mr. van Mierlo at the occasion of his retirement from active politics. He passed away 11-3-'10 RIP great guy.

 

Not all non-boring pictures are worth looking at.

[Guest trond]

Still, sharpness is not all there is to a memorable picture. Most iconic pictures are not very sharp, in fact! Sharpness is the fetish of boring photographers.

 

The aberrant old man

 

Dear Lars,

 

You are hitting the nail on the head here!

 

I must confess that I take sharp images, and I am one of those fetish "photographers" you mention; I can make sharp images of anything.

 

They all fall in the category that Ansel Adams call "a sharp image of a fuzzy concept", but they are very sharp, perfectly so, to the diffraction limit, or any other limits that the equipment may have.

 

Beeing my M9, my M3, my Practica LTL-3 or my Cambo 4X5 with APO-Sironar 135mm f5.6; they all make very sharp images.

 

I am not ashamed to say that I take great pride and joy in handeling the equipment, my Leica and other cameras. They have given me frothy years of "sharp images of fuzzy concepts".

 

As an engineer, I admire the "no compromise" (almost) laid down in the design of Leica equipment. This alone (almost), makes it worthwhile to pursue photography as a hobby for me. And once in a while, a good picture just accidentally results as an added benefit.

 

I also know quite a few other "fethish photographers", that take at least as great joy in handling their equipment, and admiring the craftsmanship of camera and lens desing, of which Leica is the very pinnacle, just as much, or even more so than the "quality" of the pictures they capture.

 

My LightRoom database counts approx 45000 images, scanned or native digital, most of them disturbingly sharp images of fuzzy concepts.

 

Private images that I look at almost every day, some of them I share with my close friends, and we laugh at them, these sharp images of fuzzy concepts from our common memories.

 

Then I realize that I can not, but hope to at least some day, capture one image similar to those Thorsten Overgaard makes.

 

There are much more joy to photography, for many people, than "fuzzy images of sharp concepts". Those images are the happy fortune of the very few of us.

 

In the meantime, we do what we are best in; discuss diffraction, aberration and other effects that diverts the focus of not being able to make a good image, sharp or fuzzy, of a clear and well tough through concept.

 

Best regards

 

Trond

 

PS: By the way, I have also done punch cards., paper punch and 8 inch floppys.

 

"The old man from the days of tube computers"

(Sorry Lars I could not resist, won´t happen again)

[k-hawinkler]

So the 400 f5.6 Telyt goes from f5.6 to f32. Used on an M9, when does diffraction become noticable?

 

Thanks, K-H.

[jaapv]

According to Erwin Puts the best performance of this lens is between f8.0 and f11.

[SJP]

....Praktica LTL-3....

Fun! I started with a P-thread Soligor, great camera for learning SLR stuff. I gave it to the kid next door about 8 years ago, hoping he would do something with it. Prolly a bad decision.

[k-hawinkler]

According to Erwin Puts the best performance of this lens is between f8.0 and f11.

 

Jaap,

 

Thank you very much. That's good to know. I have to try that next.

 

Below is a shot from my backyard of Truchas Peak in the Sangre de Cristos.

Distance from the foreground trees to the mountains about 22 miles. My distance to the trees about a quarter mile.

Shot at f32 with M9 and 400mm f5.6 Telyt. I just got the lens and it's a lot of fun.

 

Thanks again, K-H.

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

[lars_bergquist]

According to Erwin Puts the best performance of this lens is between f8.0 and f11.

When budding press photogs asked heir superiors at what f-stop some particular telephoto lens was sharpest, they usually got the answer "wide open". The main problem for a press photog is not absolute optical definition, but shake and subject movement -- and the effects of both are at a minimum there.

 

Coarse reproduction screens, and sloppy printing on shoddy paper made absolute definition very moot indeed. Our problems may be different, but lens performance must always be judged in the light of the user's requirements and preferences. MTF and the optical bench are important criteria, but these are just the bottom line.

 

The aberrant old man

[pgk]

..... lens performance must always be judged in the light of the user's requirements and preferences.

What an excellent piece of common sense! Well put Lars.

 

Just as a comment, I own a Canon 85/1.L2 and used to own a Leica R80/1.4. I used both on a Canon 5D. In terms of absolute sharpness wide open the Canon is undoubtedly better. Wide open the 80D is dreamy and slightly soft rather than producing the biting crispness of the R lens. At f/8 however the 80R produced stunningly good, highly detailed images with beautiful tonality - IMO better than the 85L. It was though slower to use and since this is not a focal length that I use all that often I finally shed the 80R. BOTH are very good lenses, if the 80R had been faster to use on the 5D I'd have kept it, but for the work I use this lens for the 85/1.2L simply made more sense to retain.

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Hallo,

Look here: Leica M

[lars_bergquist]

Well thanks. Still, personal preferences are subjective, and requirements intersubjective, at best. So no general conclusions can be drawn from them. Technical performance however, as long as you measure it by open criteria and reproducible methods, can be generalized: This is how good it can get. The rest is up to you.

 

The aberrant old man