Lens__ Circle of confusion

[joho]

first of all best wishes for the year 2024!!!

Now to the qustion WTF is meant by Circle of confisoin of a lens ???????????

is it the circle of the fstop??? focused ight to unfocued light???

[wikipedea does not count]

joho

[joho]

Forum: Lenses & Lens Accessories would be better for this ---ops!! I am cluless how to move it ...

[xkaes]

245154

[Dan Fromm]

The circle of confusion is the diameter of the largest tolerable blur circle. What's tolerable depends on the photographer's and viewers' preferences and on how much the negative is to be enlarged. It is subjective. There are arbitrary rules of thumb, but arbitrary means subjective.

[John Layton]

Somewhat tangential (sagittal? axial?:rolleyes:) musing here...but I also find that lenses of higher resolving power generally have less acceptable depth of field "tolerance" than do lenses of equivalent focal lengths which otherwise resolve somewhat less, a characteristic which can present a paradox in seeking to balance needs of sharpness and depth.

This (visual) effect can be somewhat mitigated by knowing where on the aperture scale diffraction begins to become evident, as this can be used to "smooth out" the transition between sharp and increasingly unsharp ("confused") areas in a given image.

The trick is finding a balance which still allows the "sharper" lens to remain visibly sharper (than the less sharp lens) while also providing a close to comparable acceptable depth of field. Kind of like knowing just how much of that puffer fishes' liver one can consume before it becomes fatal. (Jeesh...where did That come from:confused:).

[Mark J]

The blur circle than Dan/Xkaes refer to is the spot image that the lens produces from a perfect point in the scene.
The whole concept of acceptable blur circle depends very much on what size of print you are going to make, and how close you are going to view it.
It can hence be the basis of a lot of argument.
For a lot of DoF tables for 35mm lenses, the circle of confusion was based on what would be only just perceptible softness on an 8x10" print from the neg when viewed at arm's length so that make sense as 0.025mm on the neg as per the snip that Xkaes provided, I have also seen 0.03mm quoted.
For a contact print from an 8x10" neg, the circle of confusion could be a fair bit bigger, maybe 0.15mm.

John, you make a good point, and in fact some aberrations will help to extend the perceived depth of focus. Also, the perception of something going out of focus depends quite a lot on what you have nearby for comparison as 'sharp' . If the in-focus image from eg. an Apo lens is really crisp, it's more obvious that the subject is drifting out of focus.

[pgk]

There is also the confusion circle which is the one in which photographers have a circular argument about the others.

[John Layton]

Another definition would be a board of directors sitting around a circular table. The bigger the table....

[Drew Wiley]

It means you get confused trying to figure out why it's even important. Dan explained it best. It's a malleable rubber-band concept, one which I personally ignore. It might just mean it's time to clean your glasses, or magnifying loupe, or lens. Mr Magoo would understand.

[lassethomas]

Well sharpness is not absolute, its a gliding scale from from perfect sharp towards unsharp. Circle of confusion is a way to define when sharpness becomes unsharp. The larger circle the more unsharpness is defined as sharp. If that makes sense.

So with a larger circle you get a a larger depth of field, since you allow more unsharp distances to be defined as sharp.
All very subjective as stated above and dependant on image goals, film size, printed magnification
and more…

[Louis Pacilla]

Another definition would be a board of directors sitting around a circular table. The bigger the table....

That's pretty funny John!

[pgk]

Rule of thumb; prints become shaper when viewed from further away.:eek:

[xkaes]

WTF is meant by Circle of confisoin of a lens ???????????

joho

Lenses don't have circles of confusion. People have circles of confusion. The C-O-C is a personal choice -- but most people just choose to ignore it.

It's basically what you accept as in focus or not in focus. That's why it's related to depth-of-field.

Just as you choose the depth-of-field, by selecting the f-stop, you can choose a circle-of-confusion -- what you accept as "in focus" at any f-stop. At a given f-stop, as YOUR PERSONALLY CHOSEN C-O-C increases the D-O-F will increase -- and vice-versa. On the other hand, a narrow D-O-F means a smaller C-O-C -- there's less in focus.

DOFMASTER lets you create your own D-O-F scales for each of your lenses -- BUT you have to tell it what C-O-C you want to use in order for it to compute the D-O-F of each lens at each f-stop. It has a default setting, of course, but it's completely up to you to decide how much you consider to be in focus. The smaller you set the C-O-C, the narrower the D-O-F will be -- so less will be in focus. It's all a matter of preference.

Here's the link:

https://www.dofmaster.com/custom.html

[Alan Klein]

The blur circle than Dan/Xkaes refer to is the spot image that the lens produces from a perfect point in the scene.
The whole concept of acceptable blur circle depends very much on what size of print you are going to make, and how close you are going to view it.
It can hence be the basis of a lot of argument.
For a lot of DoF tables for 35mm lenses, the circle of confusion was based on what would be only just perceptible softness on an 8x10" print from the neg when viewed at arm's length so that make sense as 0.025mm on the neg as per the snip that Xkaes provided, I have also seen 0.03mm quoted.
For a contact print from an 8x10" neg, the circle of confusion could be a fair bit bigger, maybe 0.15mm.

John, you make a good point, and in fact some aberrations will help to extend the perceived depth of focus. Also, the perception of something going out of focus depends quite a lot on what you have nearby for comparison as 'sharp' . If the in-focus image from eg. an Apo lens is really crisp, it's more obvious that the subject is drifting out of focus.

So on a Nikon lens for example, where they stamp onto the lens barrel the f stop range for each f stop, what size in numerals does that equate to?

[Dan Fromm]

So on a Nikon lens for example, where they stamp onto the lens barrel the f stop range for each f stop, what size in numerals does that equate to?

If you're asking about the lenses' depth-of-field scales, the diameter in the circle of confusion used in calculating the scales is an unpublished arbitrary number, usually larger than a picky photographer would select.

In other words, if you have a question about Nikon's practice, ask Nikon.

[Eric Woodbury]

Perceived sharpness is a combination of resolution and contrast. Without one there is no other.

In other words, don't worry about it. Do the best you can and it's fine. Many a great photograph created with less than optimum sharpness.

[Drew Wiley]

The circle of confusion began once people dove into it. Try to find a way out.

[John Layton]

Yes indeed...when a previously finely focussed point becomes visibly softer and visibly "enlarged," we see this as "confusion," and this in increasing increments as this "circle" gets larger.

I guess where this terminology fails for me is in the use of the word "circle."

True a circle can be used to define the outer visible "diameter" of an AREA of "visible confusion," but there is no actual visible circle, excepting perhaps for certain optics like mirror-based lenses, or in certain instances where certain types of light sources (in concert with optics) can begin to acquire a circular affect as they become less focussed in an image.

But I cannot right now think of another term which so handily refers to this optical principle. ("area of confusion,?" "zone of unsharpness,?"). Hmmm...maybe when the morning coffee kicks in I'll have an epiphany!

[Alan Klein]

Yes indeed...when a previously finely focussed point becomes visibly softer and visibly "enlarged," we see this as "confusion," and this in increasing increments as this "circle" gets larger.

I guess where this terminology fails for me is in the use of the word "circle."

True a circle can be used to define the outer visible "diameter" of an AREA of "visible confusion," but there is no actual visible circle, excepting perhaps for certain optics like mirror-based lenses, or in certain instances where certain types of light sources (in concert with optics) can begin to acquire a circular affect as they become less focussed in an image.

But I cannot right now think of another term which so handily refers to this optical principle. ("area of confusion,?" "zone of unsharpness,?"). Hmmm...maybe when the morning coffee kicks in I'll have an epiphany!

Range of focus.

[xkaes]

If you're asking about the lenses' depth-of-field scales, the diameter in the circle of confusion used in calculating the scales is an unpublished arbitrary number, usually larger than a picky photographer would select.

In other words, if you have a question about Nikon's practice, ask Nikon.

Exactly. Whether the DOF scale is on a Nikon, Minolta, or Yashica/Tomioka lens, it's just the manufacturer's personal decision. If you want less "blur", just use the next-smaller-f-number scale. For example, after focusing, instead of using the scale for f8, use the scale for f5.6 -- but keep the aperture at f8.

[xkaes]

Yes indeed...when a previously finely focussed point becomes visibly softer and visibly "enlarged," we see this as "confusion," and this in increasing increments as this "circle" gets larger.

I guess where this terminology fails for me is in the use of the word "circle."

True a circle can be used to define the outer visible "diameter" of an AREA of "visible confusion," but there is no actual visible circle, excepting perhaps for certain optics like mirror-based lenses, or in certain instances where certain types of light sources (in concert with optics) can begin to acquire a circular affect as they become less focussed in an image.

But I cannot right now think of another term which so handily refers to this optical principle. ("area of confusion,?" "zone of unsharpness,?"). Hmmm...maybe when the morning coffee kicks in I'll have an epiphany!

The term "circle" does conjure up the idea of a halo for many people, and perhaps a better term would have been "ball", "globe", or "sphere" of confusion, but those are 3-D concepts. "Area" or "Zone"? Perhaps. I think I'd prefer "BLOB of confusion".

[xkaes]

Range of focus.

Range of in-focus focus.

[Alan Klein]

Exactly. Whether the DOF scale is on a Nikon, Minolta, or Yashica/Tomioka lens, it's just the manufacturer's personal decision. If you want less "blur", just use the next-smaller-f-number scale. For example, after focusing, instead of using the scale for f8, use the scale for f5.6 -- but keep the aperture at f8.

I used to do that all the time. Calculate the DOF using charts or the lens scale and then stop down one additional stop.

[rawitz]

I used to do that all the time. Calculate the DOF using charts or the lens scale and then stop down one additional stop.

Better stop down 2 steps, this was the consensus in the 70th among professional photographers when the high resolution films like Kodachrome film came and the new generation of HR optics from Nikon, Canon, Leitz ao. The "official" 35film COC of 0,03mm is a conventional value (not physical calculation like f-stop) out of the phototechnic of nearly 100 years ago. But we still find it today in the standard DOF calculation.
For HR digitalcameras, the COC should be even smaller. Fuji defines for the DCameras GFX a COC of 0,01mm.

Second odd is that the DOF calculation is not relating to film-, sensor- or lensresolution, but to a reference print of f.e. 10x FFfilm to 240x360mm. As this reference printsize 240x360mm is fixed, for the larger filmsizes like 120film the COC grows up to 0,05mm and so on.
But this will equalize the PQ advantage of the larger filmsizes, so who needs it?

regards Rainer

[xkaes]

That's a convenient way of doing it.

[Alan Klein]

This app allows you to calculate DOF based on film or sensor size. You can also select the COC size.
https://www.dofmaster.com/dofjs.html

[Alan Klein]

This app allows you to print out a chart for DOF based on film or sensor. (auto setting .1 for 4x5 and .2 for 8x10 - is that good?) You can also select the COC size manually.

https://www.dofmaster.com/doftable.html

[xkaes]

This app allows you to print out a chart for DOF based on film or sensor. (auto setting .1 for 4x5 and .2 for 8x10 - is that good?) You can also select the COC size manually.

https://www.dofmaster.com/doftable.html

That's the link I provided in Post #13.

[Alan Klein]

That's the link I provided in Post #13.

Oh I didn;t realize it. I have one of these charts printed out for each of my lenses. Here's one I marked off to quickly show hyperfocal criteria.

[Joseph Kashi]

For a full generalized explanation, check out “Airy Disk” on Wikipedia.

[xkaes]

I have one of these charts printed out for each of my lenses. Here's one I marked off to quickly show hyperfocal criteria.

I started out using home-made, DOF graphs -- one for each lens with near & far lines for each f-stop (Y-axis) and distance (X-axis).

Once I discovered the DOFMaster, DIY, rotating scales, I switched to those. Very easy to make with card stock and laminate sheets. You can make them any size you want -- and includ any details you want, at whatever Circle of Confusion you want. Here's one for FIVE lenses. I've set mine up for only TWO lenses each -- much more manageable:

245376

http://www.subclub.org/fujinon/dof.htm

[Drew Wiley]

For circle of confusion authenticity, view your calculation disc or chart with vaseline smeared over your glasses.

[reddesert]

Yes indeed...when a previously finely focussed point becomes visibly softer and visibly "enlarged," we see this as "confusion," and this in increasing increments as this "circle" gets larger.

I guess where this terminology fails for me is in the use of the word "circle."

True a circle can be used to define the outer visible "diameter" of an AREA of "visible confusion," but there is no actual visible circle, excepting perhaps for certain optics like mirror-based lenses, or in certain instances where certain types of light sources (in concert with optics) can begin to acquire a circular affect as they become less focussed in an image.

But I cannot right now think of another term which so handily refers to this optical principle. ("area of confusion,?" "zone of unsharpness,?"). Hmmm...maybe when the morning coffee kicks in I'll have an epiphany!

It's a filled circle. I don't think that is the confusing part for most people.

Other terms that could be used include "disk" (commonly used for the Airy disk as someone mentioned), and "spot size." Spot size is how optical designers sometimes talk about the theoretical size of the image of a point source that is produced by the design. But that's a different use, because that spot size is a property of the optical design, while the circle of confusion in a depth of field calculation is a property of focus: even a hypothetical perfect lens has limited depth of field.

[pgk]

In all honesty, a circle of confusion is a theoretical construct intended to illustrate what we see empirically. It rarely represents an actual reality. But it is helpful in keepig photographers happy whilst discussing what it might explain.

[Tin Can]

Good one!

Since my vision is very poor

I use DOF calculators on every shot

Tape measure, string, chart






Range of in-focus focus.

[phdgent]

Correct me as a non native English speaker, but I thought that the correct English expression was: circle of diffusion and not circle of confusion?
I find it a bit confusing...

[phdgent]

Rule of thumb; prints become shaper when viewed from further away.:eek:

I was told: twice the diameter was the good distance.

[xkaes]

Correct me as a non native English speaker, but I thought that the correct English expression was: circle of diffusion and not circle of confusion?
I find it a bit confusing...

You say po-tate-o and I say po-tah-to
You like to-mate-o and I like to-mah-to
Potato, potahto, tomato, tomahto
Let's call the whole thing off

[pgk]

I was told: twice the diameter was the good distance.

But doesn't that depend upon how sharp you want the print to look?

[Dan Fromm]

Correct me as a non native English speaker, but I thought that the correct English expression was: circle of diffusion and not circle of confusion?
I find it a bit confusing...

confusion. Also confusing, but that's a different idea.

[Daniel Unkefer]

It causes mucho confusion LOL. It's how sharp do you want the print to be. Are you going to put your nose up to it to examine?

[Drew Wiley]

What is the circle of confusion to the Marlboro Man cigarette billboard 30 feet wide next to the highway, blown up from a substandard 35mm frame to begin with - a yard across? Now such outdoor advertising mainly relies on re-programmable multiple pixel panels, with the pixels themselves often nearly that big. So, not exactly circles of confusion, but more like squares of distraction.

Now of course, the Marlboro Man and Joe Camel are frowned upon, and those same freeway positions now carry giant pot advertisements.

[xkaes]

...blown up from a substandard 35mm frame to begin with ...

I don't consider my subminiature formats "substandard", nor do I consider my larger formats "superior". They are different, of course. For example, if the film is the same, the submini lenses actually produce sharper images -- on the same size piece of film. I won't magnify the submini images as much as the larger negatives, but they do quite well for what they are. Some would say they are magnificent.

[Drew Wiley]

xkaes - It's not the relative value of the format itself I was referring to, but the fact that the most prolific Marlboro shot was a rather poor representation of what even 35mm film can do to begin with - not all that sharp, and probably cropped too. And then that gets magnified perhaps up to 500X (!!!) for sake of a large highway billboard. But a freeway is not an art museum, and driving past at 80mph isn't exactly quality viewing time. Just a glance gets the point across for those tempted to smoke. ... But having grown up among real cowboys, they had to prove their own macho with something even more raunchy and carcinogenic - either Old Golds or roll yer own. They even called them "coffin nails", and later in life regretted it. I'm more annoyed by the visual clutter of outdoor advertising than anything else.

[xkaes]

There's no confusion in this circle:

245454

[Drew Wiley]

Ha! I had an uncle who owned a small chain of drugstores and was trying to quit smoking. So he ordered up a private-labeled batch of cigarettes for his stores in black wrappers with a white cross on it, labeled, "Cancer Brand" cigarettes, with a large print hazard warning. He was selling them to other people trying to stop smoking too (it did work for him). But then Reynolds Tobacco sued him, and he had to stop selling them. Anyway, off topic, so I'll leave it at that. ... well, almost. Now that the billboards have switched to another kind of smoke, I heard a cute joke recently : "Why is Colorado voting to pass another pot bill? Because they forgot they already passed one". The huge pot ads along the freeway here are mostly just giant colored text - not even a confused image.

[reddesert]

Correct me as a non native English speaker, but I thought that the correct English expression was: circle of diffusion and not circle of confusion?
I find it a bit confusing...

I've always seen "circle of confusion." That is mostly a photography term, not an optical science term. Generally (in English) diffusion refers to a different type of physical process, a multiple scattering process, like how dye diffuses in water, and would not be appropriate for the effect of defocusing. Places where "diffusion" arises in photographic optics would be the opal glass in a diffusion enlarger, or a soft-focus filter diffuser, for example.

[Tin Can]

I smoked only Camel Straights no filter for a time

Nobody ever “bummed” one

Age 7 I rolled oak leaves

Horrible


There no confusion in this circle:

245454

[xkaes]

"Why is Colorado voting to pass another pot bill? Because they forgot they already passed one".

It looks like New Mexico "got us beat":

Marijuana Buyers From Texas Fuel a ‘Little Amsterdam’ in New Mexico

Sunland Park, along the Rio Grande, has joined the ranks of U.S. cities transformed by state cannabis laws. But the good times may not last forever. (https://www.nytimes.com/2024/01/07/us/marijuana-new-mexico-sunland-park.html?unlocked_article_code=1.Mk0.hrwr.g7hOZVoh9xB0&smid=url-share)

[Drew Wiley]

On a trip through the desert a few years ago I had stop at the first gas station available. It was called, Gas and Grass - a discounted pot if you filled up your gas tank. Reminds me of a local oil-changing service called Lube and Latte. Maybe they recycle. Would I really want to drink that?

[Doremus Scudder]

Correct me as a non native English speaker, but I thought that the correct English expression was: circle of diffusion and not circle of confusion?
I find it a bit confusing...

I guess we should be serious for a while and clear this up. The responses you've got so far are indeed humorous, but not really to the point :)

The Circle of Confusion (CoC for short) is a function of focus. At sharpest focus, a lens makes a spot, not a point, since there are always some aberrations and imperfections in the lens. As that spot is defocused (e.g., changing lens-to-film distance), it becomes a circle, which grows in size the more out-of-focus the spot gets (aperture affects the growth of the CoC, hence small apertures for more depth of field). This is the CoC. I'm not sure how the word "confusion" got attached to this, but that's the term.

Diffraction causes a similar phenomenon, but the defocused areas in this case are called Airy Discs. Again, I'm not sure why the nomenclature ended up this way. Diffraction is always present, caused by the scattering/bending of photons as they pass an edge. Smaller apertures cause more apparent diffraction because the diffraction quotient of the total light passed is larger at smaller apertures.

"Diffusion" usually refers to the spreading of a concentrated substance through a less concentrated carrying medium, such as water or air, till equilibrium is reached. Think of a sugar cube slowly dissolving in your tea until it is all equally sweet. See https://en.wikipedia.org/wiki/Diffusion

Best,

Doremus

[xkaes]

Well, now I'm confused. Are you saying our diversions and digressions were diffusions or diffractions?

[Drew Wiley]

They were differentially distracted diversions. Think of cone of confusion, and not just a circle.

[Mark J]

Diffraction causes a similar phenomenon, but the defocused areas in this case are called Airy Discs. Again, I'm not sure why the nomenclature ended up this way.

The Airy Disk came from Astronomy, George Airy. It's most applicable to resolving double-stars.
It is really only present at best focus - outside of this, a ring structure develops which may or may not have a spot or disk at the centre.
It's helpful when we're talking about a simple case where we are just looking at the image of a bright point or a star. Otherwise it's more useful to know the cut-off frequency associated with a given f/number, which is relevant to MTF on general subjects.

Note however that the CoC used to generate DoF tables does not consider diffraction effects like this.
In many cases ( especially 35mm format ) the airy disc structure is a lot smaller than typical CoC values, eg. at apertures like f/5.6 or f/8.
In LF, though , at apertures like f/45 or f/64, the diffraction structure gets quite big and fuzzy, so the best-focus is not as good. This does affect perceived DoF, in a way that John was saying, where 'out of focus' depends to some extent on what you have nearby to compare it to.

[reddesert]

The Circle of Confusion (CoC for short) is a function of focus. At sharpest focus, a lens makes a spot, not a point, since there are always some aberrations and imperfections in the lens. As that spot is defocused (e.g., changing lens-to-film distance), it becomes a circle, which grows in size the more out-of-focus the spot gets (aperture affects the growth of the CoC, hence small apertures for more depth of field). This is the CoC. I'm not sure how the word "confusion" got attached to this, but that's the term.

Diffraction causes a similar phenomenon, but the defocused areas in this case are called Airy Discs. Again, I'm not sure why the nomenclature ended up this way. Diffusion is always present, caused by the scattering/bending of photons as they pass an edge. Smaller apertures cause more apparent diffraction because the diffraction quotient of the total light passed is larger at smaller apertures.

"Diffusion" usually refers to the spreading of a concentrated substance through a less concentrated carrying medium, such as water or air, till equilibrium is reached. Think of a sugar cube slowly dissolving in your tea until it is all equally sweet. See https://en.wikipedia.org/wiki/Diffusion


Doremus, in your second paragraph you wrote "Diffusion is always present ..." but obviously meant to write "Diffraction is always present ..." - just for clarity.

"Confusion" in imaging can refer to when individual sources are unresolved and blur together into a background, like a double star that is not resolved by the eye (or the smooth-ish appearance of a highly out of focus background). That's probably where circle-of-confusion came from.

The Airy function is the point spread function of a ideal filled circular aperture (it's the Fourier transform of the filled circle with a sharp edge), so for example a telescope with diffraction-limited optics, in the absence of atmospheric turbulence, would render star images as Airy discs. Real telescopes often have central obstructions, which modify the Airy pattern slightly, and atmospheric seeing usually blurs the image out so you don't actually see multiple Airy rings, but they are there. For photographic imaging in pictorial situations, the image blur size is a combination of the effect of diffraction, non-ideal optics, and defocus, and the relative importance of these terms depends on the f-stop in use.

[Alan Klein]

I guess we should be serious for a while and clear this up. The responses you've got so far are indeed humorous, but not really to the point :)

The Circle of Confusion (CoC for short) is a function of focus. At sharpest focus, a lens makes a spot, not a point, since there are always some aberrations and imperfections in the lens. As that spot is defocused (e.g., changing lens-to-film distance), it becomes a circle, which grows in size the more out-of-focus the spot gets (aperture affects the growth of the CoC, hence small apertures for more depth of field). This is the CoC. I'm not sure how the word "confusion" got attached to this, but that's the term.

Diffraction causes a similar phenomenon, but the defocused areas in this case are called Airy Discs. Again, I'm not sure why the nomenclature ended up this way. Diffusion is always present, caused by the scattering/bending of photons as they pass an edge. Smaller apertures cause more apparent diffraction because the diffraction quotient of the total light passed is larger at smaller apertures.

"Diffusion" usually refers to the spreading of a concentrated substance through a less concentrated carrying medium, such as water or air, till equilibrium is reached. Think of a sugar cube slowly dissolving in your tea until it is all equally sweet. See https://en.wikipedia.org/wiki/Diffusion

Best,

Doremus

Don't forget "refraction" when using underwater cameras: Light bends as it passes from one medium to another. This bending of light is known as refraction, and can occur when light traveling through water passes through the glass and air of your underwater camera. Refraction underwater causes objects to appear approximately 25% larger/closer than they actually are causing a magnification effect.

https://www.scuba.com/blog/understanding-light-for-underwater-photography/

[Mark J]

Hopefully refraction takes place when we use cameras in air - otherwise we'd all be in big trouble.

[phdgent]

I guess we should be serious for a while and clear this up. The responses you've got so far are indeed humorous, but not really to the point :)

The Circle of Confusion (CoC for short) is a function of focus. At sharpest focus, a lens makes a spot, not a point, since there are always some aberrations and imperfections in the lens. As that spot is defocused (e.g., changing lens-to-film distance), it becomes a circle, which grows in size the more out-of-focus the spot gets (aperture affects the growth of the CoC, hence small apertures for more depth of field). This is the CoC. I'm not sure how the word "confusion" got attached to this, but that's the term.

Diffraction causes a similar phenomenon, but the defocused areas in this case are called Airy Discs. Again, I'm not sure why the nomenclature ended up this way. Diffusion is always present, caused by the scattering/bending of photons as they pass an edge. Smaller apertures cause more apparent diffraction because the diffraction quotient of the total light passed is larger at smaller apertures.

"Diffusion" usually refers to the spreading of a concentrated substance through a less concentrated carrying medium, such as water or air, till equilibrium is reached. Think of a sugar cube slowly dissolving in your tea until it is all equally sweet. See https://en.wikipedia.org/wiki/Diffusion

Best,

Doremus

Thank you Doremus, at last a serious answer!

Now I have to 'transfer' this as I have the impression that the therms and expressions you quoted can change during translation.
"Confusion", for instance, has so many different equivalents through translation in Flemish/Dutch all having a completely different (contradicting) contents, even in physics, hence my initial question...

[pgk]

Don't forget "refraction" when using underwater cameras: Light bends as it passes from one medium to another. This bending of light is known as refraction, and can occur when light traveling through water passes through the glass and air of your underwater camera. Refraction underwater causes objects to appear approximately 25% larger/closer than they actually are causing a magnification effect.

Except with dome ports which produce a virtual image at 4r from the centre of the dome's sphere:o.

Actually its a wonder that we ever get 'sharp' images with all these complications. I would suggest that photography is, in practice, an essentially empirical activity and (although in my case my original background was in photoscience) we gain experience and as we doo we start to understand many of these and other interactions intuitively because we assess the images produced and learn from them. Digital has speeded this process up.

In generalist photography I am unsure just how much of the science behind image creation is relevant, although it is often interesting and can at times provide an insight into observed phenomena.

Still, what would photforums be without something to discuss and argue about?

[Tin Can]

We used to have angry drunks

arguing

they few were deleted

[Alan Klein]

Except with dome ports which produce a virtual image at 4r from the centre of the dome's sphere:o.

Actually its a wonder that we ever get 'sharp' images with all these complications. I would suggest that photography is, in practice, an essentially empirical activity and (although in my case my original background was in photoscience) we gain experience and as we doo we start to understand many of these and other interactions intuitively because we assess the images produced and learn from them. Digital has speeded this process up.

In generalist photography I am unsure just how much of the science behind image creation is relevant, although it is often interesting and can at times provide an insight into observed phenomena.

Still, what would photforums be without something to discuss and argue about?

Yes dome ports do correct but my Nikonos didn't have one. I shot through the Nikonos lens directly. The other thing is that refraction works through an underwater mask as well. So everything appears 1/3 (25%?) closer to your eyes as well as to the film. The issue is that when you're shooting let's say a 35mm lens, refraction causes the lens to "see" as if it is a 50mm lens due to the refractive magnification.

[Doremus Scudder]

Doremus, in your second paragraph you wrote "Diffusion is always present ..." but obviously meant to write "Diffraction is always present ..." - just for clarity. ...

Corrected. Thanks!

[Doremus Scudder]

Thank you Doremus, at last a serious answer!

Now I have to 'transfer' this as I have the impression that the therms and expressions you quoted can change during translation.
"Confusion", for instance, has so many different equivalents through translation in Flemish/Dutch all having a completely different (contradicting) contents, even in physics, hence my initial question...

phdgent,

I can't help with Flemish, but maybe the German will give you a starting place.

Circle of confusion = Zerstreuungskreis
Airy disc = Airy Scheibchen

Best,

Doremus

[Doremus Scudder]

... For photographic imaging in pictorial situations, the image blur size is a combination of the effect of diffraction, non-ideal optics, and defocus, and the relative importance of these terms depends on the f-stop in use.

Yes, indeed. There's a sweet spot between DoF and diffraction effects that I always seem to be trying to hit. Final print size (and viewing distance) make a big difference here too. I won't hesitate to use f/45 (on 4x5) when needed, but then try to keep print size down to 11x14" or smaller.

Best,

Doremus

[xkaes]

Yes, indeed. I won't hesitate to use f/45 (on 4x5) when needed...

Best,

Doremus

For me, f22 is just a number, not a wall. There are times when I need to climb over it. And since I like macro work, f16 can become f45 very easily.

[Drew Wiley]

Depends on the size of your enlargements. Diffraction starts visibly kicking in with 4x5 by 20X24 print size when viewing close-up, or possibly even in a 16X20 print. I try not to go past f/32 with 4X5, or f/64 with 8x10.

[xkaes]

I try not to get very close to my very large prints. With a little practice, it's quite easy.

[Drew Wiley]

People get nose up to mine. I strategize them that way - the push/pull of distance. I want the general composition to be compelling from further away, yet to draw the viewer in to explore the detail over and over again, and keep discovering new things, not only in detail, but actual composition. If I can enjoy a big print on my own walls for decades, then I consider it a success. But when I need a break into my alter-ego, I pick up the Nikon and some grainy film and make poetic little prints which might not be truly sharp at any level.