DPReviewTV: What is diffraction in photography?

AlanF

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Really? Wow - that's sooo great to hear, since I'm a fellow PL4 user.

I've always been completely amazed at how the "Prime" output could take my grainy (but sharp) Olympus M43 photos and output them with super smooth beautiful backgrounds with great detail. Now I can do the same with my even better R5 photos, and not feel like I'm missing out since I avoid the Adobe products.
Unfortunately, DxO doesn't have a module for the 100-500mm yet and so you can't use their lens sharpness tool. I am using Topaz to sharpen as it's much better than Adobe's tools. The 100-400mm II, 400mm DO II DxO modules work with the R5 and sharpen up nicely. DxO are a pain being slow with new models, but it makes you appreciate it when you can use it again.
 
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stevelee

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No it won't. I have two really big issues with the video, first, he is demonstrating a visual diffraction between f17 and f96, at which point f17 looks pretty darn good. Besides, I don't know any Canon lenses that stop down past f32.
Just yesterday I was taking some shots of the woods with the 100–400mm II and messing around with Av mode to vary depth of field. I took one shot at f/36 for grins. The variable aperture works on both ends, so you can get f/36 at 400mm but not 100mm.
 

privatebydesign

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Just yesterday I was taking some shots of the woods with the 100–400mm II and messing around with Av mode to vary depth of field. I took one shot at f/36 for grins. The variable aperture works on both ends, so you can get f/36 at 400mm but not 100mm.
And how much did the diffraction destroy your image?
 

stevelee

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And how much did the diffraction destroy your image?
Not nearly as much as the noise did at 12,800 ISO. The result, when resized for posting was good enough that I put it in the winter thread.

A 100% crop, however, shows a lot of noise.

f36.jpg


For comparison, here is a 100% crop from a shot at f/5. The much smaller depth of field is the reason for what is unsharp in it. It was shot at ISO 640.

f5.jpg
 

dilbert

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But my understanding is diffraction is a function of f value (and magnification) not apparent aperture size. Well obviously it is more complicated than that, it is a function of airy disc size in relation to magnification, that is why diffraction changes with the same lens on a different sized sensor.

The Airy Disc (Airy is a noun, not adjective, as it is named after a person), is a result of diffraction. The size of the Airy Disc is a function (or result) of diffraction, which is related to the f-number.
 
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Sporgon

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The size of the Airy Disc is a function (or result) of diffraction, which is related to the f-number.
The size is also effected by the wave length of light, red being larger which makes diffraction slightly worse, and is an unfortunate aspect of physics as landscape photography is often at its best during the 'golden hour'.
 
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johnhenry

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Armchair scientists like him REALLY gloss over the math behind the optical effect of diffraction.


First off, the math is truly awful. You need to dig into complex math concepts Fourier Transforms before you even begin to understand the hows and whys of why this occurs.


In the simplest of cases, using a drastically simple form, your subject consists of white and black areas. The wavefront originates here with all subjects at infinity for the sake of argument.

As the lens focuses this, and it passes through the aperture of the lens, it imposes certain characteristics on the light that passes through to become and image at the focal plane.

The sharp edges of the diaphragm diffract light from the bright regions to the dark ones, but this is a wavelike function, there ends up being more in some regions, less in others.

With the lens wide open, lens aberrations are more pronounced. As the lens is stopped down more and more, this diffraction begins to be more noticeable, leading to unsharp transitions in light to dark areas.
 

AlanF

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Armchair scientists like him REALLY gloss over the math behind the optical effect of diffraction.


First off, the math is truly awful. You need to dig into complex math concepts Fourier Transforms before you even begin to understand the hows and whys of why this occurs.


In the simplest of cases, using a drastically simple form, your subject consists of white and black areas. The wavefront originates here with all subjects at infinity for the sake of argument.

As the lens focuses this, and it passes through the aperture of the lens, it imposes certain characteristics on the light that passes through to become and image at the focal plane.

The sharp edges of the diaphragm diffract light from the bright regions to the dark ones, but this is a wavelike function, there ends up being more in some regions, less in others.

With the lens wide open, lens aberrations are more pronounced. As the lens is stopped down more and more, this diffraction begins to be more noticeable, leading to unsharp transitions in light to dark areas.
Although Fourier Transform is the standard procedure for analysing diffraction patterns, you don't need it to understand diffraction. Sir Lawrence Bragg, the founding father of solving the structures of crystals, including proteins, by X-ray diffraction, for which he got the Nobel Prize in 1915, formulated Bragg's law from the most simple of equations https://en.wikipedia.org/wiki/Lawrence_Bragg (As an aside, I met him in the 1970s, and isn't it remarkable that people alive today could have met someone who won a Nobel prize 106 years ago.) Airy solved the equations for the Airy Disc diffraction using just differential calculus, without Fourier Transforms, and published it in Transactions of the Cambridge Philosophical Society in 1834. I recommend downloading the volume https://archive.org/details/transactionsofca05camb as it contains some remarkable papers.

Transactionsofca05camb_Airy.jpg
 
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Joules

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Armchair scientists like him REALLY gloss over the math behind the optical effect of diffraction.

First off, the math is truly awful. You need to dig into complex math concepts Fourier Transforms before you even begin to understand the hows and whys of why this occurs.
r/iamverysmart
 

AlanF

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Perhaps we could get Craig'a phrase substitution to incorporate your interpretation, ;). There are two extreme types of physicists; those who develop theories etc by simple force of mathematics, and those who think their way into a problem using intuition and visualisation, and then find the maths to continue. Einstein and Feynman are examples of the latter. Schwinger, who shared the Nobel Prize with Feynman, is an example of the former. I need to understand in my mind what is going on and I am pretty poor mathematician.
 
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Joules

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Perhaps we could get Craig'a phrase substitution to incorporate your interpretation, ;). There are two extreme types of physicists; those who develop theories etc by simple force of mathematics, and those who think their way into a problem using intuition and visualisation, and then find the maths to continue. Einstein and Feynman are examples of the latter. Schwinger, who shared the Nobel Prize with Feynman, is an example of the former. I need to understand in my mind what is going on and I am pretty poor mathematician.
I can't say that I quite understand your first sentence. But just in case somebody took offence, I was just poking fun at the poster for using glossing over the 'truly awful' maths as criticism. Essentially ignoring that there is value in understanding the effect somethig has, even if its origin and inner workings remain a mystery. After all, Newtonian physics is still highly relevant despite not 'accuratelty' describing why things like for example gravity do what they do. Nothing too serious, I just found it funny.

On another node, isn't Einsteins work on relativity more an example of predictions beginning in math and only making their way to experimental and visual validation later on? That's just what I thought based on some tidbits of information I heard over time.
 
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AlanF

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I can't say that I quite understand your first sentence. But just in case somebody took offence, I was just poking fun at the poster for using glossing over the 'truly awful' maths as criticism. Essentially ignoring that there is value in understanding the effect somethig has, even if its origin and inner workings remain a mystery. After all, Newtonian physics is still highly relevant despite not 'accuratelty' describing why things like for example gravity do what they do. Nothing too serious, I just found it funny.

On another node, isn't Einsteins work on relativity more an example of predictions beginning in math and only making their way to experimental and visual validation later on? That's just what I thought based on some tidbits of information I heard over time.
It was the way he set about it. For example, for Special Relativity he began by imagining what would happen to time etc if he was sitting on a beam of light, observing events and then thinking his way through the consequences, and then getting involved in more and more complex mathematics and General Relativity. He once said, In physics, imagination is more important than knowledge. I think this was a riposte to Max Planck who had earlier written that Experiment is the only means of knowledge at our disposal, the rest is poetry, imagination (both quoted from memory). The opposite approach is to start with equations and solve them and see where it leads.
 

Mt Spokane Photography

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It was the way he set about it. For example, for Special Relativity he began by imagining what would happen to time etc if he was sitting on a beam of light, observing events and then thinking his way through the consequences, and then getting involved in more and more complex mathematics and General Relativity. He once said, In physics, imagination is more important than knowledge. I think this was a riposte to Max Planck who had earlier written that Experiment is the only means of knowledge at our disposal, the rest is poetry, imagination (both quoted from memory). The opposite approach is to start with equations and solve them and see where it leads.
That is my understanding. Some people actually develop a theory by intuition and then set out to do the math. I find answers to simple problems pop into my head, then I do the math and I'm pretty close. My math ability is pretty poor. I managed to make it thru advanced math in engineering school in the mid 1960's. We used slide rules and mechanical calculators. It was difficult and a lengthy process to solve some of the problems that required multiple iterations. I never want to do that again.
 
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SteveC

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That is my understanding. Some people actually develop a theory by intuition and then set out to do the math. I find answers to simple problems pop into my head, then I do the math and I'm pretty close. My math ability is pretty poor. I managed to make it thru advanced math in engineering school in the mid 1960's. We used slide rules and mechanical calculators. It was difficult and a lengthy process to solve some of the problems that required multiple iterations. I never want to do that again.

All that happened when calculators became common is the problems became longer (because you could work them faster), and you were expected to have more digits of precision.

I had a cheap slide rule with me in exams in case my calculator died; but I would have choked anyway; I would have had to set the problem up (to at least get partial credit) but all I ever really learned to do on a slip stick was multiplication (and the cheapass slide rule I just mentioned could probably do little more than that anyway).
 

usern4cr

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All that happened when calculators became common is the problems became longer (because you could work them faster), and you were expected to have more digits of precision.

I had a cheap slide rule with me in exams in case my calculator died; but I would have choked anyway; I would have had to set the problem up (to at least get partial credit) but all I ever really learned to do on a slip stick was multiplication (and the cheapass slide rule I just mentioned could probably do little more than that anyway).
Slide rules taught me a lot more than just low precision multiplication. They showed the beauty of logarithms, and how they could apply to all sorts of things in real life. Like the intensity of sound or perceived brightness - it's all logarithmic. And why just mention multiplication without mentioning division? And what about the "old school" way of teaching us how to do long division on paper? Or finding square roots on paper? It taught more than just a method to forget once obsolete, but how interesting tricks could be figured out to solve difficult problems.

Oh well, it's time to go back to typing on my multi-core Apple computer with more abilities than probably existed when they put a man on the moon! :ROFLMAO:
 

stevelee

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Slide rules taught me a lot more than just low precision multiplication. They showed the beauty of logarithms, and how they could apply to all sorts of things in real life. Like the intensity of sound or perceived brightness - it's all logarithmic. And why just mention multiplication without mentioning division? And what about the "old school" way of teaching us how to do long division on paper? Or finding square roots on paper? It taught more than just a method to forget once obsolete, but how interesting tricks could be figured out to solve difficult problems.

Oh well, it's time to go back to typing on my multi-core Apple computer with more abilities than probably existed when they put a man on the moon! :ROFLMAO:
Your cell phone may have more computing power than NASA had in 1969.
 
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Mt Spokane Photography

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Slide rules taught me a lot more than just low precision multiplication. They showed the beauty of logarithms, and how they could apply to all sorts of things in real life. Like the intensity of sound or perceived brightness - it's all logarithmic. And why just mention multiplication without mentioning division? And what about the "old school" way of teaching us how to do long division on paper? Or finding square roots on paper? It taught more than just a method to forget once obsolete, but how interesting tricks could be figured out to solve difficult problems.

Oh well, it's time to go back to typing on my multi-core Apple computer with more abilities than probably existed when they put a man on the moon! :ROFLMAO:
I hated things like Bessel Functions where we had to do calculations on those huge old mechanical calculators that could multiply and divide to many decimal places but we did it over and over and had to get every one of the many digits put in correctly. They were needed for wave propagation theory. In my case, it wasn't light waves, but electromagnetic waves.

Since slide rules were a critical tool for engineers at the time, we all had good ones. I still have a couple laying around, 59 years old this year, I bought them in the fall of 1961. I still use the triangular architect's scale I bought then, its right here in my desk. When calculators came out, a simple 4 function one cost something like $450. HP was king until TI came out with much less expensive ones that did not use reverse polish. I bought a SR50 instead of a HP35.
 
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SteveC

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Slide rules taught me a lot more than just low precision multiplication. They showed the beauty of logarithms, and how they could apply to all sorts of things in real life. Like the intensity of sound or perceived brightness - it's all logarithmic. And why just mention multiplication without mentioning division? And what about the "old school" way of teaching us how to do long division on paper? Or finding square roots on paper? It taught more than just a method to forget once obsolete, but how interesting tricks could be figured out to solve difficult problems.

Oh well, it's time to go back to typing on my multi-core Apple computer with more abilities than probably existed when they put a man on the moon! :ROFLMAO:

Much of that I learned to appreciate anyway without a slide rule!
 
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