the myth of DIFFRACTION

[jcuknz]

With the 'standard' adopted by PSNZ of 1024x768 pixels for projected presentations you don't need long lenses if you have camera resolution. As I found when using my E-PL1 and 14-42 and shooting from the wrong side of the street, it is 'only' 12Mp
Sorry OP! I'm getting away from diffraction.

[Colin Southern]

Sorry OP! I'm getting away from diffraction.

Na - keep cropping aggressively and we'll be back on track with diffraction before you know it

[rhadorn]

This is certainly a driving force for some. Personally, I feel it's a personality trait that walks a fine line between "perfectionism" and "Excessive/Compulsive Disorder" - and I don't say that whilst "looking down my nose" at others, as I very much walk that line myself every day.

Having just made that confession, I might add that I have to fight hard not to cross that line; it's often been said that photographers never really finish an image - they just abandon it at some point (and I can relate to that). What I've had to learn is that - in the real world - nothing is ever perfect and that THAT'S OK. If an image has a bit of diffraction because it was shot at F22 when F16 would have done the job - and it's not as perfect as it could have been (but still looks great) then THAT'S OK.

I totally agree with all of this, admitted it holds for all possible technical limitations in a picture, as long as they are not all cumulated in the same picture

Reto

[Colin Southern]

I totally agree with all of this, admitted it holds for all possible technical limitations in a picture, as long as they are not all cumulated in the same picture

Reto

Photography is ultimately, always a compromise; at some point though, one just has to accept the limitations of their equipment - themselves - and the sheer physics of the art/science, and just "let it go" ...

... or it just drives ya nuts

[IanCD]

I have also seen wonderful pictures which were totally out of focus. This could also be a good argument against caring for limiting diffraction.

I don't share your viewing scheme. I don't look at big enlargments from a greater viewing distance: I look at pictures at various distances, going closer, retreating further away... I do the same with paintings, sculptures...

The importance of caring for detail also varies with the style of the pictures you take or want to show.

The objective impact of diffraction can be measured and compared to other limitations of lenses. But this is not the only issue. The importance of limiting diffraction is also a matter of practice, depending on the style of pictures you like to take, how you look at pictures. A photographer can consider a marginal benefit as important to him. If limiting diffraction seems to be a matter of opinions, it is only because the presuppositions are never made explicit - or because the experts take their presuppositions as universal. The importance of limiting diffractions is not only a scientific matter, but a matter of jugement, as is very well shown in the citations proposed by Glenn.


Why are there so many people around who absolutely want to be the (only) ones who are right?

Reto

Excellent points well made, Reto

[tresise]

I've often wondered why resolution would get better, then worse with decreased aperture size - do the authors provide an explanation of this

?

Basally the text books do it is not a 'new' issue - but it is a very complex subject and the maths is horrible, putting it very simply as aperture changes from wide to small, some of the aberration of which there a number decrease, so the lens resolution gets better. But then other issues start to get worse, (some never actually go away at all). So then the resolution then declines.

As a general rule the best resolutions is 3 stops down from full aperture, this is well known and in the text books - well the ones I used at University on optics etc. The problem is people try to analysis an image with out understanding what they are actually looking at and then draw the wrong conclusions which confuse them and others. Because they just don't understand all of the different issues that come into play in the real world.

This is is a complex subject with professors just in camera optics - so 'dumbing it down' (in the best possible way) so it is more understandable has huge risks.

Basically a camera lens is a massive compromise, as each element of a lens introduces errors and aberrations; some of these are then corrected or reduced by another lens element, but never eliminating the errors. The refractive index and type of glass used also reduces the quality of the image, which also depends on how accurate the batch of glass is made. The most expensive lens (ie 10ks of pounds to buy) can have there design adapted to take into account the actual refractive index of the glass to be used.

The simple point is no camera lens you or I can buy on the market is 'perfect' and it can never can be.

[Colin Southern]

The simple point is no camera lens you or I can buy on the market is 'perfect' and it can never can be.

I agree.

I think it's far MORE important for photographers to not lose sight of the forest whilst focusing on individual trees. Don't ruin the image trying to save the pixels.

[tresise]

I think you need to consider the type of Degree in Photography, you would be right if you are talking about and an Arts degree. Mine was a BSc - so we had to do all of the Physics, Chemistry, Maths etc relating to Photography so yes I had to attend lectures in the subject. I still have my copies of University Optics Vol 1+2, Tenquist, Whittle, Yarwood, and a copy of Applied Photography Arnold, Rolls, Stewart. But that was in the 1970s so still in the very early days of Photonics from what I can find.

Why? Because it is a complicated matter of science so unless you are a physicist or at least have some advanced mathematics knowledge it is very difficult to follow the mathematics formulas of diffraction.

And I agree - and from the text books relating purely to a camera lens "Diffraction limited optical systems are very high quality systems, free of optical aberrations which otherwise mask the diffraction effect."

And no camera lens (Nikon Canon etc) designed for type of photography we are talking about here on the market today is free from free of optical aberrations.

side note The Richard Feynman lectures on youtube are fascinating.

[tresise]

Dave if you happened to be a subject matter expert in your daily job and know your subject well, whatever the subject area may be in.

If some one comes along and says things which sound very plausible etc and some parts are correct, but from your knowledge you actually know have errors in them what would you do? After checking the text books etc and finding what you recall to be correct would you not say something?

[Adrian]

This thread had passed me by until today. And having perused the three pages and the CIC tutorial (which was clear and helpful) I am struggling to understand the motivation of the thread. It seems that a poster makes a judgement about the intellectual capabilities of others, and an assumption that amateurism can be equated with ignorance. This seems a weak scientific starting point. In the end though what it seems to come down to is that in order to optimise the result of photography (a a picture) it is helpful to understand the limitations of lenses.

I would struggle to understand the complex technicalities picked up on a BSc photography course. This is because I only have a law degree... and a higher degree in pure mathematics. I guess I will just have to live with that. Oh well, back to taking amateur photographs.

PS: having derided CIC for an allegedly inaccurate article back when this thread started, I have not seen clear analysis here of what is wrong with it. Just assertions.

[tresise]

lose sight of the forest

I agree and part of that is understanding what actually is important - having trained in the science of photography BSc my concern is with the accuracy of some of the information on this website. It is not accurate enough and the discipline behind some of the statements and conclusions drawn and the illustrations of the science involved is on occasions highly spurious, (certainly as in a 'spurious correlation'). Basically moving raw science into the real world with out taking into account what actually happens when you build a camera lens.

I would have never gotten away with some of the statements on this website, as a student my lecturers would have shot me down - and if others are using this as a source of information then there is a duty that in the information is totally accurate and ideally should be written by subject matter experts - certainly when statements do not match up with the texts books then it should be challenged, otherwise nothing will change.

Which is why I wrote the original piece some time ago, and from the responses I don't expect I will get many people agreeing with me on the science. Which is a shame because not only are people missing the tree/forest but the whole landscape.

Let me put it this way all of the science behind photography, which is endless debated here, I used every day in a practical way for well over 25 years, solving technical problems which included working for a major camera manufacture, another role was for Photochemistry manufacture I have also worked for Europe's largest photo-processing lab. I was also a Medical photographer and worked at the British Library. More recently as part of a digital imaging project covering many million items I researched the process of 6 of the key London based museums and galleries and the two key academic institutions in London which relate to image processing and Photographic science.

Hence I do feel confident in my knowledge and background and many of the issues I can answer very well with out checking the text books. Others questions I go through the ones I have and other on-line text books to check if I am correct ideally having a proper reference if I can.

Hence when I came across something which does not match what the text books actually say of is poor science in the sense it is a statement with no actual proof or based on an miss-understanding of the science then yes I do challenge it.
But if you know a particular subject well would you not also say when something is not correct?

[Black Pearl]

In comedy if your retort is delayed by more than a second or two it is deemed void...there's a very good example of this in the movie Shallow Hal.

Following this line of thought, after what period of time can a thread be resurrected and the posts still be of any relevance?
A week? Possibly
A month? Just about
A year? I think we're stretching it a bit thin
Over a year and a half? Really?!?!

There's a pretty good chance some of the original protagonist could be dead, some might have found a form of private enlightenment and are now living in mud hut singing songs and writing prose, some might have taken even taken thousands of photographs in the mean time and understand how these things affect real photography. Or everyone might still be sitting in front of their screen with hair down to their knees, nails so long they have to type with their wrists at ear level and skin so fragile from lack of light that the merest hint of sun would burn them to a crisp but still holding that bated breath in anticipation.

There are a few big mights in there I'll grant but you never know.

[Colin Southern]

I agree and part of that is understanding what actually is important - having trained in the science of photography BSc my concern is with the accuracy of some of the information on this website. It is not accurate enough and the discipline behind some of the statements and conclusions drawn and the illustrations of the science involved is on occasions highly spurious, (certainly as in a 'spurious correlation'). Basically moving raw science into the real world with out taking into account what actually happens when you build a camera lens.

I would have never gotten away with some of the statements on this website, as a student my lecturers would have shot me down - and if others are using this as a source of information then there is a duty that in the information is totally accurate and ideally should be written by subject matter experts - certainly when statements do not match up with the texts books then it should be challenged, otherwise nothing will change.

Which is why I wrote the original piece some time ago, and from the responses I don't expect I will get many people agreeing with me on the science. Which is a shame because not only are people missing the tree/forest but the whole landscape.

Let me put it this way all of the science behind photography, which is endless debated here, I used every day in a practical way for well over 25 years, solving technical problems which included working for a major camera manufacture, another role was for Photochemistry manufacture I have also worked for Europe's largest photo-processing lab. I was also a Medical photographer and worked at the British Library. More recently as part of a digital imaging project covering many million items I researched the process of 6 of the key London based museums and galleries and the two key academic institutions in London which relate to image processing and Photographic science.

Hence I do feel confident in my knowledge and background and many of the issues I can answer very well with out checking the text books. Others questions I go through the ones I have and other on-line text books to check if I am correct ideally having a proper reference if I can.

Hence when I came across something which does not match what the text books actually say of is poor science in the sense it is a statement with no actual proof or based on an miss-understanding of the science then yes I do challenge it.
But if you know a particular subject well would you not also say when something is not correct?

To use a double-negative, I don't disagree with any of what you wrote.

I DO think it's important to keep in mind "real world" though as we discuss things; photography is where science and art meet -- the "science" part is very black and white, but the "art" side is anything but. I'm very mindful of the fact that photography is full of a lot of "in theory" (one thing), but "in practice", something else). Many is the time where I've had discussions about people worried about diffraction - so to counter it they avoid shooting at anything narrower than F8 or F11 (because that's where they've been told that it kicks in) - as a result, they end up with a diffraction-free image () that's totally ruined because the shutterspeed was too fast (). Another prime example is not using high-ISO modes because of the "noise" and end up with a noise free image with motion blur. Prime -v- Zoom lenses are the same; they use a prime lens because it's "sharper" and then get perspective distortion because they had to zoom with their feet (or they degrade the image by having to crop heavily). The list is endless.

So the bottom line is that photography is ALWAYS a compromise in the real world (and it's in the real world where I do my shooting) -- and I think it's important to always keep that in mind; all to often photographers "major in minor" things, and completely cock-up the major things ... so a big part of what I see my job here as being is in helping folks see the big picture; if one needs to ruin the pixels to get the image then so be it.

So in terms of challenging things you believe to be wrong, go for it if you feel it's important. And in return, others will respond if they feel it's important.

Do keep in mind though that often lines have to be drawn somewhere; we might like to say "what goes up, must come down" - but then we started putting things in orbit and had to change that to "what goes up, must come down EVENTUALLY" - but then we started sending things off to the moon and mars and had to add "... somewhere, but not necessarily back to earth". I'm sure you get the idea.

So in summary, if you feel something in the tutorials is inaccurate then please let us know - but be warned, you'd better have your ducks in a row as the good doctor who wrote them has also studied from many of the same books you have, and also has a mountain of real-world experience. If it's something in the forums then - again - feel free to speak up; from experience though I can tell you that it can end up sucking up a LOT of time for little to no reward, because some folks just see things differently for some reason, and no amount of arguing, explaining, persuading, encouraging, threatening makes any difference!

[tresise]

PS: having derided CIC for an allegedly inaccurate article back when this thread started

Picking up on the above my original post related to diffraction in a camera lens which you or I could buy no more than that.

From the 10 Edition, The Manual or Photography page 32
"Diffraction limited optical systems are very high quality systems, free of optical aberrations which otherwise mask the diffraction effect"

So basically no camera lens you or I could buy will be free from aberrations, and these aberrations have a greater effect than diffraction. So the talk about 'seeing' the diffraction in a camera lens is not accurate, plus other real world issues come into play.

I am sure with your background in law degree and maths you will appreciate accuracy and a quote from a text book on the subject, my concern over all is that some of the information on this website does not always match the text books, or extrapolates well past them. From your maths you are better placed than me to comment on how errors in a system need to be taken into account and that considering the wavelength of light and manufacturing tolerances. Plus you should understand all the maths far better than me, mine stopped at degree level and that was a very long time ago now. If you could translate the maths into a more digestible form that would be appreciated.

Putting it another way if some one who is does not have a qualification in say Law started a website and wrote about law lifting key facts from a text book but leaving out other information and you see a discrepancy or factual error or how the law worked in practise not just in theory would you not say something?

My key point in the original post was the information did not match the text books and science and the transference of basic science did not take into account the real world issues of lens design. So is something 'allegedly inaccurate' if the text books don't agree with a website? Where do you put your faith personally I go for a text books or an article written by an expert. The overall subject is complex but covered in the text books in the original post.

But is summed up by "optical aberrations mask the diffraction effect"

Well it is now well past midnight,

[PhotomanJohn]

I am one of those folks that was very surprised to see this thread come back to life because the subject was so well covered originally. I was sure that no new words of wisdom could be forthcoming until Colin's post.

Do keep in mind though that often lines have to be drawn somewhere; we might like to say "what goes up, must come down" - but then we started putting things in orbit and had to change that to "what goes up, must come down EVENTUALLY" - but then we started sending things off to the moon and mars and had to add "... somewhere, but not necessarily back to earth". I'm sure you get the idea.

Thank you.

[Colin Southern]

I am sure with your background in law degree and maths you will appreciate accuracy and a quote from a text book on the subject, my concern over all is that some of the information on this website does not always match the text books, or extrapolates well past them. From your maths you are better placed than me to comment on how errors in a system need to be taken into account and that considering the wavelength of light and manufacturing tolerances. Plus you should understand all the maths far better than me, mine stopped at degree level and that was a very long time ago now. If you could translate the maths into a more digestible form that would be appreciated.

Not sure who you're talking to here???

[tresise]

Again I agree and your phrase "they've been told that it kicks in" plus your other examples back up my point - not accurate information and sometimes extremely poor translation to the real world, so people are mislead when the information is actually in the text books and is often very straight forward when moved to the real world, if done correctly.

And the key duck in this case is
From the 10 Edition, The Manual of Photography page 32
"Diffraction limited optical systems are very high quality systems, free of optical aberrations which otherwise mask the diffraction effect"

So far no camera lens manufacture (that I am aware of) say they have a diffraction limited lens - so diffraction is not actually the issue that people see in the quality of the images, I think you cover a good spread of the issues.

I will reserve my other ducks for the future, my confidence my be misplaced but the text books I quoted from were written by the people who taught me. Even after 36 years I can still recall some of the things my lecturer in optics said, the appropriately named Sidney Ray. Does just real world experience trump some one who with suitable qualifications? plus experience?

I fear from the response to the original post, so long ago now, is in general 'not positive' that the number and strength of the ducks may not be sufficient. If a suitable professor came on here and contradicted the site would they be listened to?

all to often photographers "major in minor" things, and completely cock-up the major things

Again I agree and my argument is around the quality of information which relates to the real world issues and sorry but inaccurate information on diffraction does not help the issue. Is my duck big enough?

The reason why I don't come on here it is now 1.15 in the morning and I should have been asleep hours ago.

[Colin Southern]

Is my duck big enough?

No. Sean addressed that in post #4.

Seems to me like you're one step behind both Sean and the original experts/authors you quote.

Either way, I'm done here. Good luck.

[tresise]

From the 10 Edition, The Manual of Photography page 32
Diffraction limited optical systems are very high quality systems, free of optical aberrations which otherwise mask the diffraction effect.

A fact is still a fact even if a lot of people don't agree, or understand or argue against it (leaving aside politicians or any other group you may wish to include - I am sure you get the drift)

If one knows the truth should one keep quiet even if it is 'unpopular', I am sure there must be some pithy quote out there about freedoms, true and changing opinions. But my original post still is still valid.

[tresise]

I was replying to Adrian post number 49 - who highlighted he has a law degree and one in higher maths. - hence being accurate in evidence etc - struth now 13.31