[angerdan]

I have posted many times, that DOF is almost meaningless in the digital era because we enlarge things so far beyond 8x10 that it has lost its real meaning now.

You mean CoC is almost meaningless?
Because DoF is independent from enlargement of image capture system.

[onlineflyer]

So, are you more or less confused at this point?

Yes, I am.

[photoptimist]

Take 2 Tylenol and you’ll feel better in the morning

Actually DoF has nothing to do with the apparent size of a point of light on the negative/sensor. It is related to the apparent size of a point of light on the final print, relative to the viewing distance.

The standard , developed for film was a point appeared to be less than 1/100 of an inch when a full frame was printed on an 8 inch by 10 inch sheet of paper.

The circle of confusion is then calculated back to the film/sensor size used.

The reason the CofC for an APS-C sensor is 0.02mm and full frame is 0.03mm is that to enlarge to 8x10 the full frame takes less enlargement than the crop sensor, and medium Format, whether 4x5 , 6x7 or what ever size you choose will be larger still on the film.

I have posted many times, that DOF is almost meaningless in the digital era because we enlarge things so far beyond 8x10 that it has lost its real meaning now.

I wouldn't say DoF is meaningless so much as to say DoF depends on how the image is viewed and analyzed.

Even back ye olden days of film, people printed 35 mm film shots at a range of sizes (4x6, 8x10, 16x24, etc.) and experienced different DoFs from the same negative depending on print size. Sure, digital has vastly expanded the range of effective print sizes: all the way from tiny thumbnails (having a sensor CoC as high as 0.5 mm and very deep DoFs) to pixel peeping a pixel shift image on a large screen display (a sensor CoC as low as maybe 0.007 mm and very shallow DoFs).

For photographers who want to carefully control what is in focus and what is not, CoC at the intended output and at the sensor level matter. Of course, the chosen CoC and calculated DoF might only be a starting point because blur from DoF issues adds to all the other sources of blur.

[othar]

Yes that is why I said light intensity. The depth of field situation is a bit of a can of worms.

As I can see, I opened the can

[ChatMechant]

Nerds.

[Dartmoor Dave]

I am terrified of getting onto the wrong side of an argument of the scale of that thread a few weeks back but I am not quite buying that statement.

Me too. Please let's not ever go there again.

For starters the image cast on the FF sensor is 50%larger (remember we have already agreed that we have to change focal length or get closer.)

Ah, so you're talking about trying to get an e........t (the word that must not be spoken) photo on two different sensor sizes. I've just been talking about the same lens on different sensor sizes at the same distance.

On that basis the image is presented by the lens at 50% higher resolution on the FF. (for a given resolution of the lens). That is a fundamental difference in the quality of the image that will carry through to the print. I think the coc change is reflecting this. And this no doubt could be worded better!

I feel I have to point out that a FF sensor doesn't necessarily have higher resolution than an APS-C sensor. On a digital sensor, that's down to megapixels rather than physical size. It's like I said before: the problem is that people keep talking about digital sensors as if they work the same way as film, but they just don't. For one thing, nobody has even mentioned the effect that resampling algorithms can have on apparent sharpness and therefore on depth of field.

[Serkevan]

I think I need context, what thread are you talking about? (I'm sorry if it's an unmentionable one, I don't remember any overly nasty discussions lately in which I was involved)

[TedH42]

Feels like way too many numbers aimed in random directions.
Trying to explain these concepts without well thought-out diagrams to explain the numbers seems to be a hopeless endeavor for my visually-oriented mind.

Verbiage just piles on, stirring the mental mud into a froth.

Yes, focal length always = focal length.
Any sort of "equivalence" without explanatory diagrams leads to mental mush, confusion, and arguments.
And I'll leave DOF as the "rule of thumb" concept that applies to MY photography.

That's the way I see it.
Not going to jump in unless I find time to make said diagrams, which is unlikely, as it would take far too much time for me. Not that I would get it right the first (or second, etc.) time anyway.

This number soup isn't helping me do my photography. And I'm not great at verbally explaining my understanding to others.

Carry on, y'all.

[Dartmoor Dave]

The reason the CofC for an APS-C sensor is 0.02mm and full frame is 0.03mm is that to enlarge to 8x10 the full frame takes less enlargement than the crop sensor, and medium Format, whether 4x5 , 6x7 or what ever size you choose will be larger still on the film.

In what way would an 8"x10" from an APS-C sensor be more enlarged than an 8"x10" from an FF sensor? Given that in both cases the original pixel resolution will have to be downsampled to fit an 8"x10"? An 8"x10" print from a 35mm film negative is an optical enlargement, but an 8"x10" print from a digital sensor isn't. It's just pixel values displayed at a certain resolution, and in the case of a print a certain dpi. The pixel values themselves have no physical size.

This next paragraph is a general question and not a reply to Lowell Goudge:

Where the heck did those 0.02mm and 0.03mm figures come from in the first place? It sounds like the sort of thing that somebody made up in a photography blog once upon a time and a zillion people have repeated since then. So it's become the internet's version of truth.

[reh321]

Okay, I understand the focal length of a lens doesn't change if you mount the same lens on a difference size sensor body but I'm trying to understand how the field of view (I believe I'm using the correct term) changes from medium format, to full frame, to APS-C. I asked this question in another thread and don't want to get into a major discussion there, so as not to thread on that thread.

So, let me be specific. It is my understand if you mount a full frame 150mm lens on an APS-C body you get a crop factor of 1.5, so the focal length equivalent is 225mm. Okay, now let's use the example of a 150mm 67 format lens.

You were correct up to this point. Any 150mm lens is always a 150mm lens, so any 150mm lens {assuming its image circle is large enough} will give the same field of view that a 1.5*150 = 225mm lens will give on a 35mm/"FF'' camera. Period. You have answered your own question.

[Lowell Goudge]

In what way would an 8"x10" from an APS-C sensor be more enlarged than an 8"x10" from an FF sensor? Given that in both cases the original pixel resolution will have to be downsampled to fit an 8"x10"? An 8"x10" print from a 35mm film negative is an optical enlargement, but an 8"x10" print from a digital sensor isn't. It's just pixel values displayed at a certain resolution, and in the case of a print a certain dpi. The pixel values themselves have no physical size.

This next paragraph is a general question and not a reply to Lowell Goudge:

Where the heck did those 0.02mm and 0.03mm figures come from in the first place? It sounds like the sort of thing that somebody made up in a photography blog once upon a time and a zillion people have repeated since then. So it's become the internet's version of truth.

It is not about resolution, it is about the combined circle of confusion on the sensor, and the enlargement ratio to get to the 0.01 inch circle on the 8x10 print, the enlargement ratio for a full frame epsensor is lower than for the APSC sensor

Within even the 20 micron circle of an APSC sensor are a lot of pixels

[Dartmoor Dave]

It is not about resolution, it is about the combined circle of confusion on the sensor, and the enlargement ratio to get to the 0.01 inch circle on the 8x10 print, the enlargement ratio for a full frame epsensor is lower than for the APSC sensor

Within even the 20 micron circle of an APSC sensor are a lot of pixels

But in what way is the 8"x10" an enlargement after downsampling? In what way would a 0.01" circle on the sensor become a 0.01" circle on an 8"x10" print? I'm seeking enlightenment here.

[BrianR]

Where the heck did those 0.02mm and 0.03mm figures come from in the first place? It sounds like the sort of thing that somebody made up in a photography blog once upon a time and a zillion people have repeated since then. So it's become the internet's version of truth.

I'm not sure where they came from originally, but I had thought they go back long before the internet. Back to when when people with 'normal' vision printed out 8x10's and viewed them from 12 inches away in 'normal' lighting. A blurred disc that's 0.03mm on your 24x36mm negative will still look 'pretty much' like a point to our eyes in the 8x10 print seen 12" away. I've seen a few papers on what the human eye can resolve, and there's always some variance, but the 0.03mm seemed like a decent compromise under the other conditions. It's at least a decent starting point, but I've no doubt that before the internet people wrote angry letters to each other arguing about it.

As to why 8x10 print at 12"? This is definitely an arbitrary condition, but it's handy to have a common starting point if you're printing up tables or putting guides on lenses. Again, angry letters about this probably kept many a postal service in business.

Flexible DoF calculators will let you adjust the CoC value to suit your use, preferably directly entering the value, but some let you adjust it indirectly by changing print size or viewing distance.

[Lowell Goudge]

I wouldn't say DoF is meaningless so much as to say DoF depends on how the image is viewed and analyzed.

Even back ye olden days of film, people printed 35 mm film shots at a range of sizes (4x6, 8x10, 16x24, etc.) and experienced different DoFs from the same negative depending on print size. Sure, digital has vastly expanded the range of effective print sizes: all the way from tiny thumbnails (having a sensor CoC as high as 0.5 mm and very deep DoFs) to pixel peeping a pixel shift image on a large screen display (a sensor CoC as low as maybe 0.007 mm and very shallow DoFs).

For photographers who want to carefully control what is in focus and what is not, CoC at the intended output and at the sensor level matter. Of course, the chosen CoC and calculated DoF might only be a starting point because blur from DoF issues adds to all the other sources of blur.

True, but when you consider the standard print was 8x10 and that was also about the size of a magazine print, the definition and even things like lens markings all got based upon that size

Yes the standard DoF calculation is a starting point, but the real point you highlight is there has to be some consideration of the final enlargement o base it on. size when you shoot or you have nothing

[Dartmoor Dave]

I'm not sure where they came from originally, but I had thought they go back long before the internet. Back to when when people with 'normal' vision printed out 8x10's and viewed them from 12 inches away in 'normal' lighting. A blurred disc that's 0.03mm on your 24x36mm negative will still look 'pretty much' like a point to our eyes in the 8x10 print seen 12" away. I've seen a few papers on what the human eye can resolve, and there's always some variance, but the 0.03mm seemed like a decent compromise under the other conditions. It's at least a decent starting point, but I've no doubt that before the internet people wrote angry letters to each other arguing about it.

As to why 8x10 print at 12"? This is definitely an arbitrary condition, but it's handy to have a common starting point if you're printing up tables or putting guides on lenses. Again, angry letters about this probably kept many a postal service in business.

Flexible DoF calculators will let you adjust the CoC value to suit your use, preferably directly entering the value, but some let you adjust it indirectly by changing print size or viewing distance.

Yep, I think that's the basic problem: the assumption that digital photography has got a relationship to film photography that it actually doesn't. Up to the point where the lens resolves an image onto the surface of the sensor, they are exactly the same. After that, they have no resemblance at all in any way.


Edit: My apologies if I've sounded angry in this thread. That wasn't my intention and I certainly don't feel any anger. Just bewilderment at why people think that a digital sensor does the same thing as a frame of film.