[Class A]

Absolutely not, @ClassA, it shows you don't understand what they do.

That may be your view, but it is far from correct.

They do not adjust to an output size, they adjust to an 8Mp reference.

These are equivalent operations.

Say you print 200 pixels per inch.

Images with a different pixel count will then result in differently sized prints (output sizes).

If you first normalise to 8MP and then print, both images will have the same output size.

It does not matter when and how the scaling down of the larger image occurs, in the process noise is reduced (unless incorrect, crude algorithms are applied).

They do not even take in to account camera format size differences.

Assuming the pixel size is constant then different MP numbers correspond to different format sizes.
In other words, the higher MP camera has a larger sensor.

In any event, they measure cameras with different sensor sizes. That's how the format inevitably comes into play, whether you think they are taking it explicitly into account or not.

To get the Print score, they merely take the real (Screen) measurements from their software, and add 3dB advantage for every doubling in the number of pixels, to their 'Screen' results.

Correctly so to account for the noise reduction that occurs when scaling down an image with more (but same-sized) pixels.

Note that if the larger format has the same number of pixels, no such downscaling-induced noise reduction takes place, however, it is then of course not needed because the pixels are larger in the larger format camera and hence are not one bit noisier than the same amount of smaller pixels of the small format.

Nothing to do with FF or APS-C.

Everything to do with format differences.

Why do you think that larger format cameras (on the whole) perform better than smaller format cameras in the DxOMark ranking?

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Last edited by Class A; 11-08-2019 at 09:37 AM.

[Class A]

The fact that my real world experience is closer to the print tab and not the screen tab is, I suppose meaningless.

Well, the "Print" tab is designed to reflect a real world experience (assuming fair comparisons of same-sized images).

I just want high dynamic range, low noise images. And my experience is that the K-1 delivers this at the print sizes I use, better than the K3 or K5 or K-01 do.

Your experience is predicted by physics.

There is nothing more practical than a good theory.

Even though some people don't understand equivalence considerations and refer to it as an "over-complication", it actually predicts the real world experience you have.

Again, DxoMark's "Print" tab is showing you these real world differences because it is designed to compare whole images rather than single pixels.

The "Screen" tab is designed to show you the difference when you zoom into both images so that you see a 1:1 pixel view. Such a comparison has to magnify the larger format image more and hence will show identical pixel-performance (provided the same sensor technology is used). That's why larger format cameras always appear to show a tighter crop of a region when the same number of pixels are displayed for both formats, because the larger format "zooms in" more when applying the different magnification factors required to display both images at 1:1 resolution

[Dartmoor Dave]

The "Screen" tab is designed to show you the difference when you zoom into both images so that you see a 1:1 pixel view. Such a comparison has to magnify the larger format image more and hence will show identical pixel-performance (provided the same sensor technology is used). That's why larger format cameras always appear to show a tighter crop of a region when the same number of pixels are displayed for both formats, because the larger format "zooms in" more when applying the different magnification factors required to display both images at 1:1 resolution

A statement as wrong as that one in as many ways as that one takes you beyond the pale, I'm afraid. It isn't even worth the effort of replying to.

[Alex645]

I say someone create a poll titled, THE LAST POST ON EQUIVALENCE. There everyone can vote on their various beliefs which should absolutely include:

a) The focal length is the focal length.
b) The depth of field is the depth of field.
c) The truth is the truth and the facts are the facts; according to the poster.
d) Always and never say always and never.
e) Doomed is doomed.

[Class A]

A statement as wrong as that one in as many ways as that one takes you beyond the pale, I'm afraid. It isn't even worth the effort of replying to.

Why, then, did you bother to reply?

Perhaps you want to educate the engineers running DxOMark since, it seems like you are suggesting they are wrong when they write:

"[The screen tab] shows the measurement values and graph derived directly from a RAW image when displayed on a computer screen at 100% magnification (i.e., one image pixel corresponding to one screen pixel)."

and

"[The print] tab displays the print performance measurement values and graph derived from a RAW image after a normalization step that transforms all images, regardless of original resolution, to an 8Mpix image. The print size we have chosen is a standard 300dpi 8x12 format, which corresponds to about the physical size of an 8Mpix image printed at 100% magnification."

If you grant the DxOMark engineers that the tool tips appearing when hovering over the "Screen" and "Print" tabs in a measurement page are accurate then perhaps you want to elaborate as to why you think that anything I wrote beyond what the tool tips already state is wrong.

Hint: Nothing I said is wrong. However, there is a learning opportunity for you, if you want to embrace it.

[Class A]

There everyone can vote on their various beliefs...

Luckily optics and physics are not about beliefs.

Everyone is welcome to their opinions and beliefs but not everyone has the privilege to have their opinions and beliefs match up with reality.

Perhaps I'm not interpreting your post correctly, but AFAIC, the problem are not "equivalence evangelists" who bore others to tears. The problem are statements that are demonstrably wrong and invite objections in order to avoid others to be mislead. This initial problem is then compounded by a resistance to accept anything as true that goes against an initially acquired (but incorrect) world view. Only in rare cases posters that mislead others by making incorrect statements about f-stops, etc. are able to see the errors in their ways. Most of the time the resistance to understanding the concepts at play is too high to allow a conversation to end without requiring the party that knows the truth to simply give up.

[Alex645]

Luckily optics and physics are not about beliefs.

Perhaps I'm not interpreting your post correctly, but AFAIC, the problem are not "equivalence evangelists" who bore others to tears. The problem are statements that are demonstrably wrong and invite objections in order to avoid others to be mislead.

As a forum where we have a huge range of participants in terms of experience, education, skills, equipment, and knowledge. Yes the science of imaging has demonstrable truths and falsehoods. But you could get a group of the world's top optical engineers or physicists and there would be some truths that they would all agree with, and some that they would disagree passionately about.

The same is true with photographers or PF members. I think the arguments are informative for both the posters and the readers as long as personal emotions can be kept in check. I just have a bad taste whenever some says a post is WRONG or they have the final answer that is absolutely the only truth. Trust in DXOmark or Dpreview or Consumer Reports, etc, is a belief that those doing the tests have no bias and are using a sample size and trial criteria that is flawless in their interpretation of the results.

I guess all I'm trying to add to the conversation is that there are those that live by the maxim, "I'll believe it when I see it."
But many live and find their truth in, "I'll see it when I believe it."
Whether we realize it or not, most of us probably do both.

[Class A]

But you could get a group of the world's top optical engineers or physicists and there would be some truths that they would all agree with, and some that they would disagree passionately about.

This is correct when it comes to the edges of current understanding. If a subject area is not fully understood yet then experts will differ in their takes one what might be the correct answer. Often they are all wrong and it takes someone new to find the correct path.

I do not agree that we are dealing with this case here as the underlying principles of imaging are well understood and there are no debates among experts.

I just have a bad taste whenever some says a post is WRONG or they have the final answer that is absolutely the only truth.

I don't know if you are talking about me.

I try to stay constructive during discussions and find myself more often at the receiving end of "you are wrong" (or "stupid" for that matter) allegations than I tell others that they are wrong.

However, I feel comfortable in stating that I am right because I understand the subject area well enough and the predicted effects can be practically demonstrated.

If you are asking for more modesty on my behalf, how would you feel if someone told you shouldn't be so sure that "1+1=2"? How would you respond to someone telling you that there are a variety of opinions and no one should ever say that their result is the correct one?

Again, I'm not sure you suggested I'm being to assertive about my "viewpoint", I just offer the above as a point of discussion if you did.

Trust in DXOmark or Dpreview or Consumer Reports, etc, is a belief that those doing the tests have no bias and are using a sample size and trial criteria that is flawless in their interpretation of the results.

Of course, blind belief or trust is always wrong.

However, if a theory predicts a certain performance difference and a measurement confirms exactly that difference, it seems unwarranted to suspect that the measurement cannot be trusted. In particular, if the same kind of measurement differences are confirmed by different sources.

I guess all I'm trying to add to the conversation is that there are those that live by the maxim, "I'll believe it when I see it."

Luckily, with the topic at hand, it is possible to show that all the talk about noise, etc. can be demonstrated to be true by taking respective images.
One just has to agree that a fair comparison requires the same image contents to be shown, i.e., if someone suggests to just compare a cropped (say APS-C) image with a larger (say FF) one with both images showing a different FOV then a fundamental discussion becomes necessary. With that understanding established, though, one just takes images and can see for oneself which party makes the correct predictions.

But many live and find their truth in, "I'll see it when I believe it."

I don't see how that can be a method of finding truth.
Belief, by definition, does not require evidence. Evidence, however, is a vital ingredient for establishing truth.

Using this second maxim, someone would only acknowledge things they happen to believe, meaning that they could many times acknowledge things that have no basis in reality.

I'd rather say
"I'll trust a theory if it is supported by evidence." and
"I'm confident discussing a subject matter if I understand it and have seen evidence that my understanding aligns with reality."

[BigMackCam]

When two or more parties who are confident in their differing beliefs fail to make any further progress in convincing each other, it's best just to respectfully "agree to disagree" and move on. I think, perhaps, we've reached that point in this thread...

[Dartmoor Dave]

When two or more parties who are confident in their differing beliefs fail to make any further progress in convincing each other, it's best just to respectfully "agree to disagree" and move on. I think, perhaps, we've reached that point in this thread...

Well said and thank you for stepping in, Mike. I'd logged into the site this morning planning to post some sort of an apologia, but I think I'll take your advice and just "agree to disagree". I don't know why I let myself get drawn into this sort of thread. It's not my usual style of interaction with other people, in the real world or online, and to have got to the point where you've felt the need to step in as a moderator leaves me feeling frankly disgusted with myself.

[BigMackCam]

Well said and thank you for stepping in, Mike. I'd logged into the site this morning planning to post some sort of an apologia, but I think I'll take your advice and just "agree to disagree". I don't know why I let myself get drawn into this sort of thread. It's not my usual style of interaction with other people, in the real world or online, and to have got to the point where you've felt the need to step in as a moderator leaves me feeling frankly disgusted with myself.

To be clear, I wasn't singling anyone out, nor objecting to the discussion per se... It was merely an observation that the strongly-held positions of those involved didn't appear to be shifting, and the discussion had ceased to be productive. I figured it was a good time to recognise that, accept it, step back and move on

[clackers]

If you keep the exposure constant -- which doesn't make sense but is your approach -- then a larger format will have shallower DOF.

Then you didn't watch the video.

If you keep everything constant, there is no difference in the Depth of Field. This is a myth, like many others concerning sensor size, that should not continue to be propagated.

If you find that an 85mm headshot on a FF camera has only one eye in focus instead of the two on an APS-C one, it's because you moved closer to the subject to compensate for the unnecessarily wider field of view. You changed the distance variable.

[clackers]

Ever wondered why there is a difference between the "Screen" and "Print" tabs at the DxOMark site?
The "Screen" tab shows you the pixel-performance.
The "Print" tab shows you the image-performance.

Now it's clear you don't understand, Class A.

They never took into account the format size. They only take into account the number of pixels, whether from a phone or a medium format camera.

So what is the difference between the Screen and Print tab?

The screen tab is real.

They measured it in the RAW file with their software.

The Print score is simply the Screen score, with 3dB added for each doubling of the number of pixels from 8Mp. It's as dumb as that. They never print some imaginary 11x8" out and measure it again.

I'll prove it. Attached are the screenshots of the K5-IIs performance, both Screen and Print, with exactly the same format size (APS-C), and we would predict that since the K5-IIS has 16Mp, double 8Mp, that there will be a cretinous 3Mp number difference. There is.

See for yourself. This is as infantile as their 'Sports' and 'Landscape' ratings, no reason anybody needs to be sucked in … IMHO it's analysis by morons for morons!

[Class A]

Then you didn't watch the video.

I must admit that I indeed didn't watch the video.

I trusted that despite their reputation for being pretty terrible when it comes to comparisons and technical explanations (they seriously argue that the Profoto B10 is as powerful as a Godox AD400 which anyone with a brain and access to both devices could convince themselves is a boatload of nonsense) that they would manage to regurgitate some facts about sensor sizes that they read somewhere.

Alas, Lee managed in his typical style in which confidence trumps knowledge to misinform his viewers.

If you keep everything constant, there is no difference in the Depth of Field.

If you keep everything constant (except sensor size, presumably) then you get two wildly different images which cannot be reasonably compared to each other.

At the 6:56 minute mark, Lee attempts to start the one experiment that makes sense:

• have both cameras at the same position (otherwise perspective would change and with it DOF).
• compensate for the larger sensor by using a longer focal length (otherwise the FOV would change and with it the light gathered, DOF upon cropping, etc.)
• keep the shutter speed the same.

His result is that the larger sensor produces an image with a shallower DOF.

This apparently contradicts the title of the video but he offers an explanation: The longer lens is responsible for creating the shallower DOF.

This explanation is wrong. While it is true that using a longer focal length reduces DOF when not changing the sensor size at the same time, the reason for that latter phenomenon is not the longer focal length as such, but keeping the f-stop constant.

You'll only see the reduction in DOF when going from a shorter to a longer focal length, if you keep the f-ratio constant, say, use f/2.8 for both a 50mm and 100mm lens.

You could achieve exactly the same DOF if you stopped down the 100mm to f/5.6. Why f/5.6 exactly? Well, DOF is determined by the aperture diameter (the entrance pupil, to be precise as @Ian Stuart Forsyth pointed out). In the case of a 50mm lens at f/2.8, the aperture diameter is 50mm/2.8 = 17.86mm. Now if you only change the focal length from 50mm to 100mm but keep the f-stop at f/2.8 then you increase the aperture diameter to 100mm/2.8 = 35.71mm. This larger light-passing port is responsible for the shallower DOF, not the the increase in focal length as such. One can prove this by stopping down the 100mm lens to f/5.6, resulting in the same 17.86mm aperture diameter we had for the 50mm f/2.8 lens.

I hope you can agree so far.

Note that f-stoppers use some nice diagrams to show why distance, for instance, affects DOF.
Have you noticed they they don't show you any diagrams to illustrate why increasing focal length changes DOF?
The reason why they don't show you respective diagrams with light rays, etc., is because there is no causal relationship between focal length and DOF.
I suspect that the actual effect -- the increase of the aperture diameter when the f-stop is kept constant -- eludes them and that they don't understand that DOF is essentially the result of a parallax effect, i.e., the larger the aperture, the more angles/positions exist to view the same point in the subject space.

To summarise: Contrary to what f-stoppers purport, DOF is not affected by focal length but by changes to the aperture diameter.

F-stoppers were correct in claiming (mainly through the video title) that a larger sensor does not produce shallower DOF per se.
They were also correct in attributing the change in DOF to the lens.
They were wrong in attributing the change in DOF to focal length.

The reason why the second image shot with the larger sensor showed shallower DOF was not because he used a focal length that was twice as long, but because he used an aperture diameter that was twice as large. Had he used the equivalent f-stop of f/5.6 for the longer lens, he would have achieved exactly the same DOF.

This is a myth, like many others concerning sensor size, that should not continue to be propagated.

The difference between "myths" and "facts" is that the former can be disproven by experiments while the latter are confirmed by experiments.

I hope you can agree that 100mm is the FF-equivalent focal length compared to 50mm on a 4/3 sensor.
It is not the same focal length (100 <> 50) but it is equivalent because the longer focal length exactly cancels out the wider FOV of the larger sensor.

For all practical intents and purposes, the combination of 50mm on 4/3 and 100mm on FF are indistinguishable. There are some real world practical implications that would allow you to experimentally determine which combination you are dealing with, but theoretically, you cannot distinguish one combination from the other.

I think you know that already. Where it gets slightly trickier is to understand that in order to keep combinations indistinguishable, one also has to change the f-stop. The reason is simple, though. We need to keep the aperture diameter the same, as the latter is responsible for determining the DOF. Hence, the f-stop on the 100mm lens must be twice as large as the one on the 50mm lens.

This tells us that the FF-equivalent f-stop for f/2.8 on 4/3 is f/5.6.

I hope you can see that this is exactly the same conversion we had to do for the focal length.
All photographers seem happy with the idea of equivalent focal lengths, i.e., the notion that you have to adapt the focal length when you change the sensor size.
Far fewer photographers understand the idea of an equivalent f-stop, i.e., the notion that you have to adapt the f-stop when you change the sensor size.

If you find that an 85mm headshot on a FF camera has only one eye in focus instead of the two on an APS-C one, it's because you moved closer to the subject to compensate for the unnecessarily wider field of view.

In the comparisons I make or assume, I never ever change the camera to subject distance.

With equivalent shooting parameters, you'll find that you cannot distinguish the FF image from the APS-C image.

You'll find that only one eye is in focus for the FF image, if you choose to use non-equivalent f-stops.
Choosing, say f/2.8, for both shots, make the f-stops look the same numerically, but we know that the equivalent (i.e., the one that achieves the same effect) f-stop for FF is ~f/4.

I hope this helps.

[Class A]

They never took into account the format size. They only take into account the number of pixels, whether from a phone or a medium format camera.

Are you reading my posts at all?

I already explained that if you keep the pixel size constant than "more pixels" automatically translate into "larger sensor".

Can we agree on simple facts like this one?

So what is the difference between the Screen and Print tab?

The screen tab is real.

The "Print" tab isn't any less "real".

The Print score is simply the Screen score, with 3dB added for each doubling of the number of pixels from 8Mp. It's as dumb as that.

What is "dumb" about that?

Your statement is equivalent to saying "If you double the distance between a light and a subject, you only get a fourth of the light on the subject. It's as dumb as that.".

Perhaps "as simple as that" applies. However, what is "dumb" about laws of nature?

They never print some imaginary 11x8" out and measure it again.

They don't need to.

Why would they expend the effort when one can calculate the outcome?

If they actually printed an 8x12 image and measured it, they would only confirm the numbers that they already obtained by calculation.

Why do you think that the ability to calculate the effect makes the effect less real?

There is no good reason whatsoever to discredit a phenomenon purely on the basis that there is a numerical way to predict its magnitude.

If you actually went through the exercise of printing two images with the output size, coming from two cameras with different sensor sizes, you could see for yourself that all the predictions/calculations are accurate. When using the same f-stop, the DOF from the larger sensor camera will be shallower and the noise levels will be lower.

This real effect maps to a calculation based on the number of pixels in an image because we are assuming that the pixel size is constant. So if a camera has two times the amount of pixels, its sensor area is two times as large.

This of course does not mean that you could observe the same effect when comparing sensors with the same size where one just happens to have a higher pixel pitch, i.e., more but smaller pixels. The noise advantages that can be computed from reducing a certain amount of pixels to a standard 8MP format only materialise if the pixel sizes are constant. I trust you already know why that is.

I hope this helps.