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Author Topic: DR, DxO, DSLR, MFDB, CMOS, CCD  (Read 18556 times)
ErikKaffehr
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« on: July 08, 2010, 03:53:25 PM »
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Hi,

There are a lot of discussion about DR (Dynamic Range) on this forum. It is quite obvious that persons with considerable experience have quite different opinion on the issue.

- One thing that I suppose we all agree on is that bigger is better as long as Depth Of Field is not an issue. A bigger sensor collects more photons and therefore will have better photon statistics. If we assume an MFDB sensor having the double area of a FX (Full Frame) sensor the theoretical advantage would be about a half stop.

- It is my understanding that normally the noise floor is dominated by shot noise (statistical variation of incident photons) and in the darks possibly by read noise. It is also my understanding that read noise is less on DSLRs than on MFDBs. The number of electrons each pixel can hold is about the same on sensors having the same pitch

So according to the above we would never see an advantage in excess of say one stop maximum on MFDBs over full frame DSLRs. DxO labs publishes detailed measurements that pretty much are consistent with the above observations.

It is my understanding that if we correctly expose right we would essentially have non specular highlights near saturation. In this case DR would show up as latitude for underexposure quite similar to increasing ISO. As a matter of fact, on MFDBs not having variable pre amplifiers underexposure would work identical to high ISO settings.

We would expect that if a camera A would have a 4 stop advantage in DR over another camera B it would perform identical to camera B at 16 times the ISO. So would an MFDB have a 4 stop advantage it would achieve the same image quality at 1600 ISO as the lesser camera at 100 ISO. But it seems that this is clearly not the case. MFDBs don't perform very well at high ISOs (except the PXX+ series).

Now, many experienced observers clearly see a 4-6 stop advantage with MFDBs over DSLRs. I don't have any issue with that, but I cannot understand where it is coming from.

It would be very nice if some could come up with a physically feasible explanation for MFDBs having a significant advantage in DR or samples clearly demonstrating the effect.

Best regards
Erik Kaffehr
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BernardLanguillier
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« Reply #1 on: July 08, 2010, 06:11:25 PM »
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Quote from: ErikKaffehr
Now, many experienced observers clearly see a 4-6 stop advantage with MFDBs over DSLRs. I don't have any issue with that, but I cannot understand where it is coming from.

Essentially one person is making these claims.

Quote from: ErikKaffehr
It would be very nice if some could come up with ........ samples clearly demonstrating the effect.

Wouldn't that be nice? Starting from clear experimental facts to build a theory?  

- there is no theoretical reason why it should be more than one stop (not at image level, even less at pixel level),
- measurments show less than one stop,
- I have never seen samples showing more than one stop

I would propose we stop all DR discussion till the day somebody shows me on actual samples more than one stop difference in DR between a P65+ anda  D3x files correctly exposed to the right. I will have zero problem to acknowledge I was wrong if presented with clear evidence.

And... please don't come and tell me it is hard to measure... if it is hard to measure then it is no more than one stop.  

Cheers,
Bernard
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deejjjaaaa
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« Reply #2 on: July 08, 2010, 07:36:39 PM »
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Quote from: ErikKaffehr
but I cannot understand where it is coming from.

you have a chance - 3 slots left - http://luminous-landscape.com/forum/index....c=44724&hl=
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« Reply #3 on: July 08, 2010, 09:48:04 PM »
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Quote from: BernardLanguillier
- there is no theoretical reason why it should be more than one stop (not at image level, even less at pixel level),
- measurments show less than one stop,
- I have never seen samples showing more than one stop

I would propose we stop all DR discussion till the day somebody shows me on actual samples more than one stop difference in DR between a P65+ anda  D3x files correctly exposed to the right. I will have zero problem to acknowledge I was wrong if presented with clear evidence.

And... please don't come and tell me it is hard to measure... if it is hard to measure then it is no more than one stop.  

Cheers,
Bernard
Unless the laws of physics are suspended, you will not see such samples demonstrating a full stop difference in DR between these two cameras. The DXO measurements, which place the noise floor for DR at a S:N of 1:1, show that the D3x has more DR than the P65+. If you set the noise floor higher, the P65+ would come out better, since the DR at the higher noise floor would be limited more by shot noise than read noise. The D3x apparently has less read noise, giving it an advantage where the noise floor is set very low.

Figure 12 of Emil Martinec's essay allows determination of the DR for a given ISO and noise floor for the Canon 1D3. One merely notes where the S/N curve for a given ISO crosses the x-axis for a given S/N and then reads off how many stops that represents on the x-axis. Where shot noise predominates, the slope of the curve approaches 0.5, whereas it approaches 1 where read noise predominates. Similar curves are available for other cameras, but apparently not for the P65+.
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ErikKaffehr
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« Reply #4 on: July 08, 2010, 10:20:20 PM »
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Thanks for the suggestion, would be interesting.

Best Regards
Erik


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ErikKaffehr
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« Reply #5 on: July 08, 2010, 10:45:56 PM »
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Hi,

I think that there are more than one. Mark Dubovoy says about six stops, but he also mentioned that Jeff Schewe came up with four stops. I think Michael Reichmann came up with a similar conclusion. Anders HK doesn't really discuss DR but sees a real difference.

I'd also like to see an explanation to the difference in high ISO performance.

Some thing I'd point out is that most compare with Canons and at least according to DxO the Canons are significantly worse contenders than the Nikon D3X.

When Michael Reichmann compared 5DII, Alpha 900 and D3X he did not test for DR but he found image quality to be quite similar at low ISO. So even when the Nikon D3X has a significantly better image quality than the Sony Alpha 900, Michael could not readily see the difference.

Another discussion, http://www.imx.nl/photo/leica/camera/page176/s2part4.html really shows a difference between the D3X and Sony Alpha 900. I don't understand where that difference is coming from, either, but it's very much visible. There has been a lot of negative remarks on Erwin's testing, suggesting he does good lens tests and bad camera tests. Erwin may even test for DR in a future article.

Best regards
Erik


Quote from: BernardLanguillier
Essentially one person is making these claims.
« Last Edit: July 08, 2010, 10:48:13 PM by ErikKaffehr » Logged

BernardLanguillier
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« Reply #6 on: July 08, 2010, 11:07:11 PM »
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Quote from: ErikKaffehr
When Michael Reichmann compared 5DII, Alpha 900 and D3X he did not test for DR but he found image quality to be quite similar at low ISO. So even when the Nikon D3X has a significantly better image quality than the Sony Alpha 900, Michael could not readily see the difference.

With all due respect to our host, his testing of the D3x was done during an antartica trip and less than 5% of his shooting was done with the D3x if I am not mistaken... Michael's focus at that time was not specifically DR by any means, and certainly not the DR of the D3x. Testing the D3x was one of his many goals during this trip and he had made it clear already that he was not that interested in that camera for various reasons.

Rightfully so. Snowy landscapes are definitely not the type of scene I would personnally pick to have a realistic understanding of the DR of a camera (I do a lot of snowy landscapes...). The only vaguely dark area is the sea and the sky where there is little detail to be found in the first place.

I have had access to A900 files and they are good for sure (probably a tad better colorwise in fact), but the shadows do not exhibit the same quality found in D3x files. There is also more noise in the mid-tones. I am telling you things the way they are, I would have zero issue with the A900 being better although it is 3 times cheaper... after a detailed computation of the cost for me (think system, lenses,...) the D3x ended up being cheaper than a switch to Sony anyway.

There has been extended discussions on why the D3x, although it is based on the same sensor as the A900, could have more DR. Simply put it is for the same reason Leaf back owners have been claiming that they backs have more DR than a ZD based on the same sensor. DR is controlled by shadow noise and the quality of the processing electronics plays a huge role here. The same can be seen in among DX cameras where the D90 has more DR than other cameras using the same Sony sensor.

Cheers,
Bernard
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ErikKaffehr
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« Reply #7 on: July 09, 2010, 12:05:49 AM »
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Hi Bernard!

I have no issue with the D3X being better than the Sony Alpha 900. In addition Nikon has Live View and Sony don't. The two things I wanted to point out was that difference between the two is clearly significant in DxO testing, but it was not really obvious in Michael Reichmann's review.  Michael compared Sony Alpha 900, Nikon D3X and Canon 5DII in studio, but he was not discussing DR. To be more specific:

DxO (whom both you and me seem to trust) say that you need about 5 points on the DxO mark to see a visible difference. The Nikon D3X and the Sony Alpha are 10 points apart, but the difference is still not very visible in Michael Reichmann's studio shots. The Nikon D3X and the Phase One P65 score quite evenly on DxO but now we suddenly have 4-6 stops in DR advantage  in some reports.

Michael Reichmann is more cautious in his own writing:

He says that

- P65+ i significantly better than Leica M9
- Leica is significantly better than Alpha 900
- Alpha 900 is significantly better than Panasonic GH1

He essentially states that there are visible and significant differences, doesn't say it's DR.

I actually don't understand how we can judge dynamic range from a print. Any print has significant manipulation of the gradation curve, we may add clarity and so on. Prints have a DR of about 7 stops so if we have more than that we need to do some tone mapping. Putting 12 stops into a DR of 7 stop without manipulation would result in a very flat print.

Regarding where the advantage is coming from would be interesting to know. It seems that the D3X has no external ADCs (?). Fourteen bit readout seems slow compared with twelve bits. Does the D3X have a different and slower on chip ADC? Someone suggested that they could take two separate readouts using different settings of on chip pre amps, but Emil Martinec says that would give a visible signature in raw files and that isn't there.

Now, if Nikon came up with a really unique idea they may probably not tell.

Also, camera electronics only affect readout noise. If we look at the Noise diagram the D3X has constantly less noise than the Sony, curves on Nikon and Sony are very similar and quite different from say Canon. But Nikon is simply better. My guess would be differences in CGA and microlenses. Another observation is that in Erwin Puts tests the Nikon is much sharper. I'd presume that is a difference in optical low pass filter, or possibly Nikon being better focused.

Best regards
Erik


Quote from: BernardLanguillier
With all due respect to our host, his testing of the D3x was done during an antartica trip and less than 5% of his shooting was done with the D3x if I am not mistaken... Michael's focus at that time was not specifically DR by any means, and certainly not the DR of the D3x. Testing the D3x was one of his many goals during this trip and he had made it clear already that he was not that interested in that camera for various reasons.

Rightfully so. Snowy landscapes are definitely not the type of scene I would personnally pick to have a realistic understanding of the DR of a camera (I do a lot of snowy landscapes...). The only vaguely dark area is the sea and the sky where there is little detail to be found in the first place.

I have had access to A900 files and they are good for sure (probably a tad better colorwise in fact), but the shadows do not exhibit the same quality found in D3x files. There is also more noise in the mid-tones. I am telling you things the way they are, I would have zero issue with the A900 being better although it is 3 times cheaper... after a detailed computation of the cost for me (think system, lenses,...) the D3x ended up being cheaper than a switch to Sony anyway.

There has been extended discussions on why the D3x, although it is based on the same sensor as the A900, could have more DR. Simply put it is for the same reason Leaf back owners have been claiming that they backs have more DR than a ZD based on the same sensor. DR is controlled by shadow noise and the quality of the processing electronics plays a huge role here. The same can be seen in among DX cameras where the D90 has more DR than other cameras using the same Sony sensor.

Cheers,
Bernard
« Last Edit: July 09, 2010, 12:09:39 AM by ErikKaffehr » Logged

John R Smith
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« Reply #8 on: July 09, 2010, 03:11:44 AM »
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An issue here is the almost total lack of hard technical information from the manufacturers. Compare that with film, where you have highly detailed specification sheets from Kodak, Ilford and so on for all their emulsions, with characteristic curves and everything you need.

The effect of different implementations of the same physical sensor would also be really interesting, beacause then we could examine how on-board processing of the image data affects the end result. For example, the same Kodak KAV 39000 sensor is used by various MF digital backs, but as far as I know no-one has compared say the Phase P45, Hass HD-39 or CFV-39 in terms of the RAW data they produce at a given ISO.

John
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« Reply #9 on: July 09, 2010, 04:16:05 AM »
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Quote from: John R Smith
Compare that with film, where you have highly detailed specification sheets from Kodak, Ilford and so on for all their emulsions, with characteristic curves and everything you need.
And then... Each film maker had its own grain measurement, and we're essentially in the same boat : if not as desirable, noise has a bit the same subjective qualities as film grain, and therefore is hard to quantify.

My 2 (euro) cents worth :
- yes, electronics quality (read noise) seems to control at least as much quality as "laws of physics" (shot noise), if not more,
- moreover, what all measurements don't show so far is noise quality : is there any pattern in noise, such as banding or blotching, making it suddenly far more objectionable even if noise level (RMS) stays the same?
« Last Edit: July 09, 2010, 04:17:12 AM by NikoJorj » Logged

Nicolas from Grenoble
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« Reply #10 on: July 09, 2010, 04:31:01 AM »
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I'll try to be as constructive as I can.

I've put a disclaimer somewhere in Lu-La about that topic.

OP's question: Why is so that persons with considerable experience have quite different opinion on the issue?

IMO, simply because all these apparently contradictory statements have a part of truth.

I don't like at all those "in between lines" sarcastic comments on Mark that are diseminated each time this topic appears.
Putting constantly an etiquette on someone's under the pretext that he was wrong in an article is not a practise I enjoy reading,
very teenager behaviour. So as we are in between men I guess, it would be nice if ones for a while we could bring that debate ahead
without pointing Mark's "heresy". Because he might not be as wrong as we think and let me explain this point.

The DxO are NOT trustable on a real basis. Until you can not recognise that fact and take the DxO measurements as only an indication of a data,
you will not be able to accept the subjectivity and apparent contradictions.

So you are trying to understand something that seems absurd and questions will emerge over and over again without being answered
because the reference you are taking is not enough.

DxO is very similar to horsepower. They measure rigurously, in a scientific way, a value called DR.
A car can have 200 horsepowers, a camera can have 11 stops DR. This is a value, based on a sort of standard of measurement.
DxO is not even a worldwide standard like for example temperature measurement. DxO is french people who decided to do some testings following a specific
methodology. Just an observation. But anyway, let's say they are trustable. They are trustable only to bring some datas that have been measured in a specific
laboratory condition.

Now, we all know that horsepower is just one element of a car's performance. There are many other parameters that can make the differences.
In those, the conditions play an important role also. DxO is not trustable, not because they are bad, but because it simply can not explains
where and when those DR differences happen. They only give a usefull indication exactly like horsepower does. But the field is another story and can contradict these facts.
If you follow the formula one championship, maybe the most tech and demanding sport, you will see that those facts happen all the time: measurements that are not
trustable in this or that circuit, who are alterated by temperature, humidity etc...
If you relly on DxO to understand why those things happen, it is like you would relly on horsepower as a fix data to understand a fact, and of course, all that falls appart.
If the most tech demanding sport is actually unable to explain the differences by measurements, I doubt a little french comitee doing testing can give you any clew.

Then, there is another factor wich is the capture and the post production.
I think that the pictures in this thread are showing an impressive DR. Tipically the situation where you would prefer having a P65 than any other gear.
6 stops? No, of course not.
I don't know the D3x capability so I won't speak about it.
But then, there is the post-production task. What's called the room. The real information contained and the recuperation capacity.
Should we call that DR ? maybe that's the clew.
But in this area, the differences are indeed big.

In controled light, I doubt that the DR differences are significatives. But in others situations, they could be.

So all those concepts are subjectives, each case being a case in itself and maybe we should also consider the use of the 2 letters DR.

Cheers.
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BernardLanguillier
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« Reply #11 on: July 09, 2010, 04:34:16 AM »
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Quote from: NikoJorj
- moreover, what all measurements don't show so far is noise quality : is there any pattern in noise, such as banding or blotching, making it suddenly far more objectionable even if noise level (RMS) stays the same?

Absolutely, not to mention hideous painterly effects at micro detail level.

Cheers,
Bernard
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« Reply #12 on: July 09, 2010, 04:51:48 AM »
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Quote from: fredjeang
Then, there is another factor wich is the capture and the post production.
Ideally, two captures of the same scene with of two different cameras will get the same treatment, so post production could be set aside in a "fair" DR comparison.

But yes, as the DR limit is essentially the one of noise in the shadows (we know how to expose don't we?), postprocessing and more precisely noise treatment can play a big role (LR users have been given a good notch more of DR with LR3 eg) and unbalance some uncareful comparisons, as well as greatly emphasize the noise structure problem (banding is not only awfully ugly, it is also much harder to reduce in postprocessing).
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Nicolas from Grenoble
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BernardLanguillier
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« Reply #13 on: July 09, 2010, 05:30:07 AM »
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Quote from: fredjeang
So all those concepts are subjectives, each case being a case in itself and maybe we should also consider the use of the 2 letters DR.

Just one question then, how do you define the "real DR" that differs from the "lab DR" of DxO?

If we are able to see 2, 4 or 6 stops of DR gap along the "real DR" axis, it must have a definition and be a measurable entity, so how is it defined?

Thanks.

Cheers,
Bernard
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« Reply #14 on: July 09, 2010, 05:37:04 AM »
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Quote from: BernardLanguillier
Just one question then, how do you define the "real DR" that differs from the "lab DR" of DxO?

If we are able to see 2, 4 or 6 stops of DR gap along the "real DR" axis, it must have a definition and be a measurable entity, so how is it defined?

Thanks.

Cheers,
Bernard
That's exactly what I think is the problem.
How do we stritcly have to use a term.

I do not have the answer to your question, but it seems that DR embrasse something too large and therefore confuse.
Remember that horsepowers have also the same issue: there are 2 measurements.
The Data horsepower and the real horsepower. They are not the same.
This has been used in car engineering to define 2 concepts that where shocking together.

That would be a great idea if we could invent a similar terminology.

Cheers.

Ps: somethinmg similar also exists in audio I think. I'm not an expert at all but I remember having heard about real power and data power.
« Last Edit: July 09, 2010, 05:38:58 AM by fredjeang » Logged
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« Reply #15 on: July 09, 2010, 06:39:28 AM »
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Quote from: ErikKaffehr
Another discussion, http://www.imx.nl/photo/leica/camera/page176/s2part4.html really shows a difference between the D3X and Sony Alpha 900. I don't understand where that difference is coming from, either, but it's very much visible. There has been a lot of negative remarks on Erwin's testing, suggesting he does good lens tests and bad camera tests. Erwin may even test for DR in a future article.

And none of the negative remarks I have seen have been accompanied with actual criticism on his methodology, and consist of unsupported dismissals, hand-waving and thinly veiled ad hominems.
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« Reply #16 on: July 09, 2010, 08:51:37 AM »
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Quote from: BernardLanguillier
Just one question then, how do you define the "real DR" that differs from the "lab DR" of DxO?

If we are able to see 2, 4 or 6 stops of DR gap along the "real DR" axis, it must have a definition and be a measurable entity, so how is it defined?

Thanks.

Cheers,
Bernard

DxO does have the requisite information if you know where to look:
http://luminous-landscape.com/forum/index....c=42158&hl=

It is a bit exasperating to continually hear this complaint about DxO.  The points about noise character are well taken however.  They can be quantified by a more refined analysis of the noise spectrum, but DxO does not do this (at least, they don't present any results on their website).
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« Reply #17 on: July 09, 2010, 10:29:07 AM »
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Emil,

What is your point on my assumption that a significant advantage (like 4-6 stop) in DR for MFDBs would also be seen as good high ISO performance?

The ideas that exposing to the right we would have highlight near saturation so the extensive DR would be on the shadow side, essentially allowing for underexposure which is essentialy the same as fake ISOs.

I started this discussion because I would like to see any feasible explanation for having several steps of advantage of MFDBs over DSLRs, or is it the emperors new cloths?

Best regards
Erik


Quote from: ejmartin
DxO does have the requisite information if you know where to look:
http://luminous-landscape.com/forum/index....c=42158&hl=

It is a bit exasperating to continually hear this complaint about DxO.  The points about noise character are well taken however.  They can be quantified by a more refined analysis of the noise spectrum, but DxO does not do this (at least, they don't present any results on their website).
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« Reply #18 on: July 09, 2010, 11:03:49 AM »
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Quote from: ejmartin
DxO does have the requisite information if you know where to look:
http://luminous-landscape.com/forum/index....c=42158&hl=

It is a bit exasperating to continually hear this complaint about DxO.  The points about noise character are well taken however.  They can be quantified by a more refined analysis of the noise spectrum, but DxO does not do this (at least, they don't present any results on their website).

The problem is you are arguing about what amounts to religion with science, which is bound to fail
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« Reply #19 on: July 09, 2010, 12:16:05 PM »
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Quote from: ErikKaffehr
It is my understanding that if we correctly expose right we would essentially have non specular highlights near saturation. In this case DR would show up as latitude for underexposure quite similar to increasing ISO. As a matter of fact, on MFDBs not having variable pre amplifiers underexposure would work identical to high ISO settings.


Erik,
This is my understanding too.

Jonathan Wienke took the trouble a few years ago to produce a DR chart which defined the concept in terms of the legibility of text, in order to cut through the subjective confusion.

Is there anyone who would claim that a camera which could not provide legible text at a specific underexposure, has a higher DR than another camera which can produce legible text in the same circumstances, using lenses of comparable quality?

The chart consisted of progressivley smaller text and numbers on different colored backgrounds.

The procedure, when comparing the DR of two cameras, was to start with a full ETTR exposure of the chart from each camera, then progressively underexpose shots of the chart with both cameras.

For example, if camera A shots which were underexposed 12 stops still revealed legible text of a certain size on the chart, which camera B shots could reveal as legible at no greater underexposure than 10 stops, then camera A could reasonably be considered to have a 2 stop DR advantage, provided that the same text at -12 & 1/3rd EV (using Camera A) and -10 & 1/3rd EV (using camera B ), were both illegible.

This method also allowed DR testing at either the pixel level or the 'equal FoV' level. To compare DR at the pixel level, the distance to the chart would be adjusted so that the shots from each camera would consist of the same number of pixels.

However, in my view, the DR at equal FoV is more significant. The camera with the higher pixel count may have a DR advantage which should not be ignored.

DXO Mark shows the D3X as having a slightly higher DR than the P65+ at the pixel level, but a slightly lower DR at equal print sizes.

It would be interesting to compare results using Jonathan Wienke's method.
« Last Edit: July 09, 2010, 12:17:24 PM by Ray » Logged
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