"Equivalence" demonstrated: Canon 5D and Panasonic GX1

Started Apr 27, 2013 | Discussions
Great Bustard Forum Pro • Posts: 40,751
The bottom line...
2

Detail Man wrote:

pidera wrote:

It is exactly these differences one sees when comparing images made using equivalent settings that make "equivalency" interesting, as they go beyond the obvious conclusions. The use of equivalent settings allows to really see difference in distortion, out of focus behaviour, sensor performance etc. That is why I prefer not to talk about equivalent images, lenses etc but merely about equivalent settings.

I agree. Attempting to grab the word "equivalent" and sling it wide as if it could encompass all realms of subjective perceptual aesthetics seems about as productive as expecting listeners of music to gather in committee and legislate precisely what musical intervals, scales, timbres, instruments, artists, and musical pieces are "better", "the same", or "worse". Aesthetics is not in itself a science.

That is a truly fool's errand, and a prescription for pretentious qualitative subjective declarations rendered meaningless when one rationally considers the lack of scruples of those who would expect to shove their subjective perceptions, preferences, and tastes down the throats of others.

There is no way that I can step into the heads of others and look through their eyes. And the reverse is also true. Therefore, such "qualitative" debates are implicilty based upon falacious premises. Why this simple but most profound variable is so commonly ignored is an eternal mystery.

It makes more sense to critique a quantitative argument on the quantitative bases themselves - and the recognizable complexities surrounding attempting to project them into qualitative perceptual realms. However, fuzzy edges do not necessarily entirely negate their (qualified) usefulness.

.

There are certain quantitative characteristics arising out of camera-lens system settings that are measurable (with varying degrees of complexity, for the most part not without aid of instrumentation).

Field of View - Easy to determine (but not as simple as Focal Length when focused at infinity).

Depth of Field - Possible to determine (but varies with any given individual viewers' visual acuity).

Signal/Noise Ratio - Possible to determine (but varies in perceived impact dependent upon the image itself, viewing conditions, and individual viewers, especially where it comes to periodic noise).

.

When we use simplified models that replace complex multi-element lens-systems with single, symmetrical thin lenses, a number of rough approximations are made when scaling settings.

(1) Effective Focal Length should be used instead of the Focal Length when focused at infinity.

(2) Scaling Focal Length as well as the F-Ratio by the ratio of the sensor Crop Factors ignores the fact that the Depth of Field (also) changes as a function of the ratio of the Camera (lens-system front nodal plane) to Subject (plane of focus) Distance to the Hyperfocal Distances involved - by an amount directly proportional to the ratio of the Focal Lengths of compared systems.

Therefore, the inter-format transformations made are only valid when the Camera to Subject Distance is substantially longer than the Focal Length, and are also only valid when the Camera to Subject Distance is substantially shorter than any of the Hyperfocal Distances involved.

(3) The relationships of image-noise to sensor size are valid only for Photon Shot Noise when the relative Quantum Efficiencies are known and also factored-in. The additional element, that is ...

... Read Noise (even the entirely random, and not periodic components of), is design-specific in nature, and does appear to reliably follow simplistic assumptions regarding scaling with photosite geometries. Further, the magnitude of (input-referred) Read Noise as well as its (output-referred) proportion (relative to the maximum recorded or recordable peak level) is camera system specific, and is thus a complicated and individualized function of ISO settings.

Therefore, quite a bit of specific actual test-data and knowledge is required in order to meaningfully make such comparisons and assumptions surrounding Signal/Noise Ratio - and such numerical comparisons may not necessarily accurately reflect viewers' subjective perceptions.

I recently proposed referring to such rough corollaries as "metametric" as opposed to "equivalent":

http://www.dpreview.com/forums/post/51322339

... but the participants involved in that particular discussion seemed too embroiled to pay attention.

.

If the interesting and somewhat useful methods of (approximate) comparison of camera-lens systems that King James (among others) ascribe to should rightly be qualified, it is for the above reasons.

However, it seems that the more common challenge arises out of seriously misguided viewpoints seemingly unwilling (or unable) to recognize the relatively straightforward and easily demonstrable differences between: Entrance Pupil Diameter and F-Ratio; Exposure proper (which has nothing to do with ISO Sensitivity) and its clear misuse when referring to Brightness; the difference between light energy per unit area (intensity) and light energy per unit image-sensor active-area (total light); and the relationship of sensor-area to Photon Shot Noise SNR.

When people are unable to grasp the fundamental principles upon which such comparisons are based, the surrounding discussions are as a result virtually doomed to ever resemble conga-lines of vociferous drop-outs from a remedial reading class insisting to teacher that up is down and 2+2=5 - and such discussions seldom transcend the painful review exercises of the first day of class.

What ensues more resembles some kind of series of belligerent assaults upon teacher - and it may be that King James is most comfortable presiding over introductory classes. No other venue attracts so may who are often in some way misguided or outright wrong to be duly corrected. A perhaps gratifying position for magister - as he able to always feel comfortably ahead of his audience.

And the insurgency should not forget that such socratic festivities are not a required course - it is they who take up the gauntlet with intention to unseat the self-proclaimed champ. The most prevalent "equivalence" that I see being assumed is one between public power and providential majesty. All who aspire to such social status face never-ending challenges to their perceived title.

DM ...

...is that those that fight against the term "Equivalent" to describe photos with the same perspective, framing, DOF, shutter speed, and display size would be happy to lay down their swords if the terms "Equivalent" were instead defined as photos with the same AOV and exposure, when, ironically, most of them cannot say whether or not f/2.8 1/100 ISO 400 has the same exposure as f/5.6 1/100 ISO 1600.

That, to me, speaks volumes.

OP walkaround Senior Member • Posts: 2,551
Re: "Adding to the confusion"

Great Bustard wrote:

Wasn't it you who said:

http://www.dpreview.com/forums/post/51377460

Equivalent images all have identical:

- ISO

- Shutter Speed

- Aperture

- Framing

Anyone who says "equivalence" means something other than the above is an idiot.

Anyone who disagrees with my definition of "equivalence" is an idiot.

Hmm.

Yes, and it was obviously sarcasm, and noted as such. But then you knew that already. Your "entertainment" continues. Sad for you that this thread will get to 150 soon. What will you do then?

coudet Veteran Member • Posts: 3,999
Re: "Adding to the confusion"
2

walkaround wrote:

Great Bustard wrote:

Wasn't it you who said:

http://www.dpreview.com/forums/post/51377460

Equivalent images all have identical:

- ISO

- Shutter Speed

- Aperture

- Framing

Anyone who says "equivalence" means something other than the above is an idiot.

Anyone who disagrees with my definition of "equivalence" is an idiot.

Hmm.

Yes, and it was obviously sarcasm, and noted as such. But then you knew that already. Your "entertainment" continues. Sad for you that this thread will get to 150 soon. What will you do then?

Equivalence threads pop up every week. Give it a few days, there will be another MFT user with inaccurate claims and people who'll correct him. It'll get to 150 posts too.

Repeat everything in 2 weeks time.

Great Bustard Forum Pro • Posts: 40,751
Re: "Adding to the confusion"

walkaround wrote:

Great Bustard wrote:

Wasn't it you who said:

http://www.dpreview.com/forums/post/51377460

Equivalent images all have identical:

- ISO

- Shutter Speed

- Aperture

- Framing

Anyone who says "equivalence" means something other than the above is an idiot.

Anyone who disagrees with my definition of "equivalence" is an idiot.

Hmm.

Yes, and it was obviously sarcasm, and noted as such. But then you knew that already.

Actually, I missed that.  Apologies.

Your "entertainment" continues. Sad for you that this thread will get to 150 soon. What will you do then?

I would like you to answer this question, which I have now posed to you three times without an answer:

If noise and DOF do not matter, then what is the difference between f/2 ISO 100, f/2.8 ISO 200, f/4 ISO 400, f/5.6 ISO 800, etc.?

Hen3ry
Hen3ry Forum Pro • Posts: 18,218
Re: You say, "An f-stop is an f-stop...
1

Great Bustard wrote:

Hen3ry wrote:

An f-stop is an f-stop, a shutter speed is a shutter speed, and an ISO is an ISO (although various manufacturers fudge the latter a little just as in the old days the film manufacturers fudged things a little in respect of sensitivity). So f2 @ 1/200 with a 25mm focal length lens on m43 produces an image of near enough to the same density and general characteristics as f2 @ 1/200 with a 50mm on FF.

...a shutter speed is a shutter speed, and and ISO is an ISO."  But apparently you stop short of focal length.  That is, you didn't say "A focal length is a focal length."

I find that omission curious.

That is, just as the effect of 25mm on mFT has the same effect as 50mm on FF, the effect of f/2 on mFT has the same effect as f/4 on FF.  And yet you feel "an f-stop is an f-stop" but apparently don't think that "a focal length is a focal length".

Like I said -- curious.

Oh, don’t be a silly Bustard! The curious thing is that you have written the non sequitur above.

The effect of focal length was implicit in what I wrote -- such as 45mm (90mm equiv).

The primary effect of focal length is viewing angle and perspective. Hence m43 45 is 35mm 90 equivalent. The aperture doesn't come into it.

DoF? Now there is where aperture matters. I’ll worry about that when I want to but basically I'm not a razor thin DoF photographer.

Total light on the sensor? In practical terms, what nonsense. As I said in my post, we went through all that stuff 50 years ago when 35mm was the small format barbarian hammering at the gates. What we want is correct exposure in our given sensor size.

For that m43 f2 25mm is equivalent to FF f2 50mm.

Cheers, geoff

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Lee Jay Forum Pro • Posts: 52,721
Re: You say, "An f-stop is an f-stop...
2

Hen3ry wrote:

The primary effect of focal length is viewing angle and perspective.

Changing focal length doesn't change perspective.  Only changing shooting location does.

Total light on the sensor? In practical terms, what nonsense.

In practical terms, that's what dictates signal-to-noise ratio, so it's only nonsense if you don't care about how much detail and noise is in your images.

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Great Bustard Forum Pro • Posts: 40,751
Re: You say, "An f-stop is an f-stop...
3

Hen3ry wrote:

Great Bustard wrote:

Hen3ry wrote:

An f-stop is an f-stop, a shutter speed is a shutter speed, and an ISO is an ISO (although various manufacturers fudge the latter a little just as in the old days the film manufacturers fudged things a little in respect of sensitivity). So f2 @ 1/200 with a 25mm focal length lens on m43 produces an image of near enough to the same density and general characteristics as f2 @ 1/200 with a 50mm on FF.

...a shutter speed is a shutter speed, and and ISO is an ISO."  But apparently you stop short of focal length.  That is, you didn't say "A focal length is a focal length."

I find that omission curious.

That is, just as the effect of 25mm on mFT has the same effect as 50mm on FF, the effect of f/2 on mFT has the same effect as f/4 on FF.  And yet you feel "an f-stop is an f-stop" but apparently don't think that "a focal length is a focal length".

Like I said -- curious.

Oh, don’t be a silly Bustard! The curious thing is that you have written the non sequitur above.

Really?  I kinda thought that was absolutely central to what is being discussed.

The effect of focal length was implicit in what I wrote -- such as 45mm (90mm equiv).

The primary effect of focal length is viewing angle and perspective. Hence m43 45 is 35mm 90 equivalent. The aperture doesn't come into it.

Sure -- if we are only talking about AOV, the f-ratio doesn't come into it.  I've said this countless times.

DoF? Now there is where aperture matters.

Also noise.  The wider the aperture, the more light that falls on the sensor for a given shutter speed.

I’ll worry about that when I want to but basically I'm not a razor thin DoF photographer.

It may interest you to know that the f-ratio doesn't come in the form "Razor thin DOF / Super Deep DOF" -- there's a range of values.

Total light on the sensor? In practical terms, what nonsense.

In practical terms, the total amount of light projected on the sensor, combined with the sensor efficiency, determines the noise in the photo.

So, what you call "nonsense" is instead a profound lack of understanding of what role exposure and total light play in terms of the visual properties of the photo.

As I said in my post, we went through all that stuff 50 years ago when 35mm was the small format barbarian hammering at the gates. What we want is correct exposure in our given sensor size.

For that m43 f2 25mm is equivalent to FF f2 50mm.

So all we want is "correct exposure"?  I kinda thought there was more to it.  By the way, if 25mm f/2 1/100 ISO 400 is "correctly exposed" on mFT, what about the exposure of 50mm f/4 1/100 ISO 1600 on FF?  Is it "incorrectly exposed"?

Yohan Pamudji Senior Member • Posts: 2,874
Re: One last stab
4

walkaround wrote:

Yohan Pamudji wrote:

What you are talking about is using the same exposure settings on 2 different formats--aperture, shutter, ISO--which will result in the same brightness

Yes. You think this is self apparent, but to others it is not. And dpreview adds to the confusion:

"Sigma's choice of F1.8 as maximum aperture isn't a coincidence; it means that the lens will offer the same control over depth of field as an F2.8 zoom does on full frame. What's more, it will also offer effectively the same light-gathering capability as an F2.8 lens on full frame. By this we mean that it will be able to project an image that's just over twice as bright onto a sensor that's slightly less than half the area, meaning the same total amount of light is used to capture the image. This is important as it's a major determinant of image quality."

(my emphasis)

The part that I put in bold above is only true (and only interesting) if your primary concern is image noise. If you are concerned, like most people taking a photograph, with "brightness" ie exposure, then it is not true. To the individual pixel or film grain the lens is an f/1.8 lens.

So you can save your explanations, I am fully aware of what the equivalence gang defines as "equivalence". I find it funny that I'm being called ignorant and insulted for pointing out what several of you have admitted is accepted fact, even "obvious".

No, you are being called ignorant for calling what you're pointing out as "equivalence", which it isn't.  And you still persist.  Nobody is disagreeing with the premise that equal exposure settings on different sensor sizes result in the same brightness.  People are just disagreeing with your claim that that represents equivalence, which it doesn't no matter how much you rage against it.

And with that I contribute another post toward 150 so this thread can die a peaceful death.

OP walkaround Senior Member • Posts: 2,551
Re: "Adding to the confusion"
2

Great Bustard wrote:

I would like you to answer this question, which I have now posed to you three times without an answer:

If noise and DOF do not matter, then what is the difference between f/2 ISO 100, f/2.8 ISO 200, f/4 ISO 400, f/5.6 ISO 800, etc.?

If I say "nothing" I suppose you will go "ha!! I got you!"... but then I clearly said I only shoot at base ISO, so noise is not important to me. I think my original post was clear. At least 14 people "like" what I was trying to show: exposure is exposure regardless of format.

OP walkaround Senior Member • Posts: 2,551
Re: One last stab
2

Yohan Pamudji wrote:

No, you are being called ignorant for calling what you're pointing out as "equivalence", which it isn't.  And you still persist.  Nobody is disagreeing with the premise that equal exposure settings on different sensor sizes result in the same brightness.  People are just disagreeing with your claim that that represents equivalence, which it doesn't no matter how much you rage against it.

Can you please point out the international body that has control over the word "equivalence"? Is there a committee somewhere? You don't like mine, I don't like yours: I guess we're even.

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