A study in lens diffraction f2.8 - f 22

Illustrates lens diffraction from aperture changes of f2.8 - f22.

Internet Archive Search: diffraction teoli

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Subject is a small section of a halftone print.

Diffraction is a determinate parameter, directly proportional to wavelength and relative aperture (f/stop). The effect it has on image quality depends on the medium, lens, and subject. Measured using a high contrast USAF target, in the day, Leica lenses were remarkable being diffraction limited at f/11. The same lenses on a modern digital camera fall off noticeably at f/8. The difference is film vs the high acutance of digital.

As one primarily shooting landscapes, I wince when stopping to f/8, and don’t recall the last time I used f/11 for anything serious.

A lens that is diffraction limited wide open, at large apertures, is remarkable. A lens that is diffraction limited at f/11 is not.

Being diffraction limited means that image degradation by any of the lens aberrations is less than the limiting effect of diffraction. At large apertures, keeping aberrations down is difficult, and the image will be worse than it might be because of those aberrations. A lens that is diffraction limited at f/2 shows the result of considerable effort and the succes thereof. At f/11, almost all lenses are diffraction limited. Nothing special.

If a lens is 'diffraction limited' at f/11 on film, but at f/8 on a sensor, the effect you see is not that of diffraction, so it is wrong to use the term diffraction limited.

I don't think diffraction "limited" is the correct way to view it. It's not as if there is a brick wall and no matter how much more resolution you have from the medium (in my case my digital sensors) it won't be recorded at a smaller aperture like f/11.

As one primarily shooting landscapes, I wince when stopping to f/8, and don’t recall the last time I used f/11 for anything serious.

Some of my lenses need to be stopped down to f/11 for various reasons. I find f/5.6 has greater acuity but I can recover sharpness from f/11 at the cost of some added artifacts/noise which doesn't show up nearly as much as some of the issues I get when shooting at wider apertures (such as a shallower DOF, soft corners from field curvature, etcetera).

There is a brick wall. Lens design plays a big part, but given a lens that is indeed diffraction limited at all apertures (a perfect lens) attainable resolving power approx. halves with every two stops you stop the lens down. You cannot do anything about it.

The resolving power of whatever medium is put behind a lens will also have an effect on what you get. But that has nothing to do with diffraction, except that you cannot capture more than what a lens gives, and what a lens gives may be limited by diffraction.

So you will not notice the effect of diffraction as long as the limit is set by the medium. Only when diffraction becomes the cause of even worse, it will be made visible by the medium.

Again, what difference you see comparing film to sensor, or film to film, or sensor to sensor, is not diffraction. It is a difference in the medium. Something else entirely.

There is a brick wall.

No, it's more like a steep slope than a cliff you go over.

...(a perfect lens) attainable resolving power approx. halves with every two stops you stop the lens down.

I'll take your word for that, though I'm totally uninterested in such a hypothetical scenario (another scenario, DOF reaches to infinity even though we don't see that far), in the real world I live in I don't see anything close to that, and testing sites correlate with what I see, so nothing remotely close to losing half your resolution when stopping your lens down from f/5.6 to f/11. Besides that, I photograph 3-D subjects with all the DOF issues that entails, so while I could theoretically gain some resolution by shooting at wider apertures and then do focus staking to get back a reasonable DOF, I find it far more practical to base my needs on a CoC that will match or exceed the medium I'm using and my intended output for resolution and make up for softness from resulting diffraction by applying sharpening during post processing.

Whatever your preferred way of dealing with the idiosyncrasies of photography is, Tony, diffraction is not hypothetical. See the samples shown.

If you don't see diffraction effects stopping your lens down from f/5.6 to f/11, it is either because you (for whatever reason) you do not pay attention, or you're not using a lens that is diffraction limited at f/5.6, or both.

It also is a brick wall, because it will not give. Whether you can use the desired CoC or not is not quite up to you.

If you are interested in CoC size, you must be interested in diffraction and its effect. Again: "real world", not hypothetical.

DoF is not involved. A red herring. Anything not in focus is unresolved far beyond what diffraction might produce at the aperture used.

Sharpening can change the appearance of what detail there is. It does not introduce finer detail than was captured. No help.

You can't correct incorrect statements by claiming you don't care.

One of the epiphanies of mirrorless digital cameras is that many lenses are sharper wide open than at f/11. We demand and get corners nearly as sharp as the center. We also have tools which can be used to focus very precisely (revealing that DOF is a useful fiction).

The falloff in resolution at smaller apertures is due not only to diffraction, but residual errors in element curvature, spacing and centering. The uncertainty of these factors add roughly as the root-mean-square of the individual values. This causes the net resolution (contrast) to be rounded, rather than a sharp peak or break in performance. Even though diffraction is calculated as a singular value, it is represented in nature as a set of concentric Airey rings. Rather than binary parameters, I prefer to think of these phenomena as uncertainties. This disqualifies me from ever being a politician or lawyer.

Whatever your preferred way of dealing with the idiosyncrasies of photography is, Tony, diffraction is not hypothetical. See the samples shown.

I went to the original link but didn't see anything there. Probably just didn't figure out what or where I was supposed to look at. Anyway, I know what I see in practice, and what testing results of sites that makes measurements show, and it's not even close to losing 50% resolution at even four stops differences in the aperture setting.

If you don't see diffraction effects stopping your lens down from f/5.6 to f/11, it is either because you (for whatever reason) you do not pay attention, or you're not using a lens that is diffraction limited at f/5.6, or both.

I see the effect, but as far as resolution recorded with my D800 and D500 is concerned with the lenses I'm using on them the differences mostly show up as sharpness rather than lost detail, and that's looking at tightly controlled shots at 100% on my computer monitor.

It also is a brick wall, because it will not give. Whether you can use the desired CoC or not is not quite up to you.

If you are interested in CoC size, you must be interested in diffraction and its effect. Again: "real world", not hypothetical.

Again, not what I've seen. I think diffraction impacted is more accurate than diffraction limited. It's like dealing with a headwind that can become strong enough to blow you over, eventually, rather than running into a brick wall.

Sharpening can change the appearance of what detail there is. It does not introduce finer detail than was captured. No help.

Again, show me this great loss of resolution. Show me anything close to 50% at two stops. Don't point me to someone else's results that you haven't yourself replicated. Show me something I can replicate for myself. After you show me, I will look at it and get back to you about that.

You can't correct incorrect statements by claiming you don't care.

The "incorrect" statement you are referring to is that this is a purely hypothetical scenario you are proposing. Am I misreading the test results from websites measuring and showing how the lenses we can buy and use on our cameras doesn't support your 50% claim? Again, show me (I don't mean to sound like I'm from Missouri).

(revealing that DOF is a useful fiction).

It's not a fiction, it's relative based on viewing distance.

...in the real world I live in I don't see anything close to that ["...(a perfect lens) attainable resolving power approx. halves with every two stops you stop the lens down".] and testing sites correlate with what I see, so nothing remotely close to losing half your resolution when stopping your lens down from f/5.6 to f/11. Besides that, I [snipped.] make up for softness from resulting diffraction by applying sharpening during post processing.

Here is an example of what I see, the four crops on the left side being 100%, focused using Live View and shot on a solid tripod using MUP with EFCS:

I will grant you that going to f/22 I do lose about half the resolution, so (again) the theory may well be true, I'm not disputing that, but (again) in the real world circa 2021 f/11 works fine for shooting landscapes with very nearly no resolution loss compared to shooting at f/5.6 (or wider), at least for any lenses I have had the opportunity to use (the above being my first really good lens dating back to when I owned a Nikon D200, and still a really sharp lens to this day on my D500).

Again, Tony, that you do not see an effect when stopping down from f/5.6 to f/11 means that resolution limiting effects of lens faults at f/5.6 are at least as great as that of diffraction at f/11.

Diffraction is real, not hypothetical. But your lens' performance at f/5.6 isn't good enough to reveal it. Your lens' performance is not limited by diffraction, it is not diffraction limited, at f/5.6.

The effect is so real and great, that most lenses are limited by diffraction at f/11 and stopped down more. Only very bad lenses are still limited to less by lens faults at those apertures. So there is nothing remarkable about diffraction limited lenses at f/11.

A perfect lens will show that resolution halves with every two stops you close the aperture down. It is, as they say, a Law of Nature.

Now, should you and i be glad that most of our lenses are not perfect?

Again, Tony, that you do not see an effect when stopping down from f/5.6 to f/11 means that resolution limiting effects of lens faults at f/5.6 are at least as great as that of diffraction at f/11.

Diffraction is real, not hypothetical. But your lens' performance at f/5.6 isn't good enough to reveal it. Your lens' performance is not limited by diffraction, it is not diffraction limited, at f/5.6.

The effect is so real and great, that most lenses are limited by diffraction at f/11 and stopped down more. Only very bad lenses are still limited to less by lens faults at those apertures. So there is nothing remarkable about diffraction limited lenses at f/11.

A perfect lens will show that resolution halves with every two stops you close the aperture down. It is, as they say, a Law of Nature.

Now, should you and i be glad that most of our lenses are not perfect?

I call bull on my lens not being good enough to show diffraction at f/5.6 or probably even a wider aperture. My sensor isn't good enough because my lens resolves to Nyquist frequency on my D500 (which is around 45 MP when scaled up to FX area). The fact is, you can't say what the limit of my lens is shooting at f/5.6 because the sensors I'm currently using don't show it.

Also, as you can see from the crops on the left side where both files came out of the Raw converter using the same settings, there is an obvious difference between using f/5.6 and f/11, but it's acuity and not resolution. I actually had to take a step back because the D500 and Tokina macro lens was resolving all of the resolution bars (if I got closer still I would be resolving the ink dots, which I have done) and I actually wanted it to reach a point where it was no longer resolving a couple of the resolution bars.

Yes, your sensor's capability to record what a lens can offer may be limited. Then we are no longer discussing diffraction.

For the rest, do read a good book on optics.

Yes, your sensor's capability to record what a lens can offer may be limited. Then we are no longer discussing diffraction.

For the rest, do read a good book on optics.

It's irrelevant to me because I'm not "diffraction limited" and neither are the vast majority of real world photographers circa 2021. Our cameras don't record diffraction at f/4 and barely at f/5.6, and diffraction even at f/11 does not effect resolution enough to make it unrecoverable (as I demonstrated above). Now if you can demonstrate otherwise then by all means do so.

In the perhaps not-so-distant future we may have camera sensors capable of showing practical diffraction limitations of our better lenses, perhaps when we reach 72 or 100 megapixels on 135/FX format sensors -- we're already there with a lot of smartphones and other smaller formats -- but even then we will be discussing enormous prints or significant crops (that would effectively put us back to working with tiny formats). Frankly, I don't see this being something I in any way need to be overly concerned about in my lifetime, and I know for a fact that we can get huge prints using FX/135 format at f/11 and not be "diffraction limited."

It's not a fiction, it's relative based on viewing distance.

I shared an apartment with a law student. The term "legal fiction" came up often. It is a construct to illustrate a point of law, but without definitive proof. There is only one plane of sharpest focus, if you can find it. At the pixel level, it is quite clear that nothing else comes close to sharp focus. At best, DOF defines a region fo "good enough" focus under arbitrary viewing conditions, which fits the use of "useful fiction."

There is only one plane of sharpest focus, if you can find it. At the pixel level, it is quite clear that nothing else comes close to sharp focus. At best, DOF defines a region of "good enough" focus under arbitrary viewing conditions,

The closer you look, the shallower the DOF becomes; conversely, as you move further away the less distinguishable any differences in focus become and the DOF correspondingly increases in depth. Also, the size of the pixels relative to the CoC can make distinguishing the focus point from other points indistinguishable precisely because you won't be able to view the focus plane any closer than that.

DoF and diffraction. Depends on how you understand DoF.

Diffraction increases the minimal attainable CoC size, so DoF as blur below the visual acuity of whoever is viewing the image under a given set of circumstances decreases.

DoF as the visual difference between sharp and unsharp increases. More DoF, but overall less sharp.

Better lenses have less DoF at the same aperture.

And yes, if the medium is not up to the job of resolving what a lens projects, we do not get to see differences in the range beyond the medium's capabilities. So more DoF, but less resolution, regardless of lens and diffraction.

The closer you look, the shallower the DOF becomes; conversely, as you move further away the less distinguishable any differences in focus become and the DOF correspondingly increases in depth. Also, the size of the pixels relative to the CoC can make distinguishing the focus point from other points indistinguishable precisely because you won't be able to view the focus plane any closer than that.

The usual method of manual focusing is to establish two points on either side of the focal plane (subjectively) eually out of focus, using the focusing ring, then divide the distance. This works reasonably well with a ground glass, and particularly well with a digital camera with the assistance of focus magnification.

Objectively, these two ring positions are well within the marked DOF, regardless of the method.

Defining DOF as the observable circle of confusion in an 8x10 print, viewed at a distance of 10 inches, is a convenient fiction, with little application to real life. The greatest fiction is the hyperfocal distance. Most of us have found landscapes turn out better if you focus precisely on the object of central interest, rather than use the hyperfocal setting which often renders every major point OOF. The same is true if you use an aperture of f/11 or smaller, except when "published" inside the 1000 pixel limit on PNet.

Alternately you can use the Scheimpflug Effect, or focus stacking.

Most of us have found landscapes turn out better if you focus precisely on the object of central interest,

Either that or use the "double the distance" method explained here: Double the Distance Method Explained (photographylife.com) (do a search on that site to discover a few more articles on focusing in landscape photography. I never got along with hyperfocal and had only limited success with Merklinger's approach; "double the distance" has the advantage of being easy to apply in the field.

One of the key advantages of MILC is that you have 100% live view, where the viewfinder (EVF) is bright enough to actually preview the DOF and its effect on the composition. I don't avoid OOF elements, I use them to isolate and complement the desired subject. Sony engineers must have similar thoughts, because even their AF lenses focus using the preset aperture. My preferred lenses are manual (Zeiss Loxia), which are strictly mechanical with DOF scales. Zeiss AF lenses (Batis) also have DOF scales, which are presented in an OLED display on the lens. However my only use of that display so far is to set the focus accurately at infinity for astro photography. (You can focus on stars only in suburban situations with a relatively bright sky. In really dark skies the EVF has too much noise to see anything.)

For those who have not been introduced, even peripherally, to the law, the concept of "a reasonable person" in determining justificaion is an example of a legal fiction. We are all expected to act reasonably, but the definition is left to the judge or jury.