Is the term ISO “totally fake”?

AlanF

Canon 5DSR II
Aug 16, 2012
5,663
2,921
There has been a lot of hot air about the inconsistency of iso among manufacturers. There is real evidence, however, to the opposite. DxOMark has been measuring for years the actual iso values for tested sensors and plotting them against the stated ones. There is in fact a remarkable consistency among the top makers I have looked at, and a consistent pattern of deviations of the manufacturers stated from the actual, as seen in these two comparisons. Such remarkable agreement among these manufacturers suggest they are attempting to conform to the standards of ISO, and maybe even their tabulated values might be correct and there are systematic errors in DxOMark's measurements (figures courtesy of DxOMark).

183356
183357
 

Michael Clark

Now we see through a glass, darkly...
Apr 5, 2016
918
439
There has been a lot of hot air about the inconsistency of iso among manufacturers. There is real evidence, however, to the opposite. DxOMark has been measuring for years the actual iso values for tested sensors and plotting them against the stated ones. There is in fact a remarkable consistency among the top makers I have looked at, and a consistent pattern of deviations of the manufacturers stated from the actual, as seen in these two comparisons. Such remarkable agreement among these manufacturers suggest they are attempting to conform to the standards of ISO, and maybe even their tabulated values might be correct and there are systematic errors in DxOMark's measurements (figures courtesy of DxOMark).

View attachment 183356View attachment 183357
Digital cameras tend to overstate the ISO. What they call ISO 400 is really more like ISO 250-320. Film was often the opposite: what was actually sensitive at around ASA 80 would be sold as ASA 64. Of course, as film ages the sensitivity goes down, so that ASA 64 that was actually ASA 80 when it was factory fresh might only be ASA 72, or even ASA 64 by the expiration date.
 

AlanF

Canon 5DSR II
Aug 16, 2012
5,663
2,921
Digital cameras tend to overstate the ISO. What they call ISO 400 is really more like ISO 250-320. Film was often the opposite: what was actually sensitive at around ASA 80 would be sold as ASA 64. Of course, as film ages the sensitivity goes down, so that ASA 64 that was actually ASA 80 when it was factory fresh might only be ASA 72, or even ASA 64 by the expiration date.
The DxOMark data do consistently show that the makers consistently overstate the isos above 100, and understate at iso 50. DxO explains this in https://www.dxomark.com/About/In-depth-measurements/Measurements/ISO-sensitivity where the detail the measuring of iso values. They say manufacturers deliberately overstate the iso to avoid clipping of highlights. But, something smells when different manufacturers have exactly the same deviations from the DxO measurements. Do you know of any other independant measurements?
 

3kramd5

EOS 5D MK IV
Mar 2, 2012
3,082
404
Digital cameras tend to overstate the ISO. What they call ISO 400 is really more like ISO 250-320.
They are supposed to round up to the nearest 1/3 stop. 321 should be reported as 400. 250 to 400 breaks both the ISO and the industry standard. I wonder if amateur comparisons are done consistency with proper conditions.
 

Kit.

EOS 6D MK II
Apr 25, 2011
1,265
682
The DxOMark data do consistently show that the makers consistently overstate the isos above 100, and understate at iso 50. DxO explains this in https://www.dxomark.com/About/In-depth-measurements/Measurements/ISO-sensitivity where the detail the measuring of iso values. They say manufacturers deliberately overstate the iso to avoid clipping of highlights. But, something smells when different manufacturers have exactly the same deviations from the DxO measurements. Do you know of any other independant measurements?
What bothers me is that in their "testing protocol" (https://www.dxomark.com/About/In-depth-measurements/DxOMark-testing-protocols/ISO-sensitivity) they don't specify the color temperature of their light source and even do explicitly mention LEDs. And then they also don't say what they do if the saturation of the different color channels happens at different exposures.
 
  • Like
Reactions: SwissFrank

flip314

EOS RP
Sep 26, 2018
231
305
I wonder what made Nikon stop at 3.2 million ISO. I want to be able to shoot at ISO 4 billion, even if there's literally zero dynamic range.
 

Berowne

... they sparkle still the right Promethean fire.
Jun 7, 2014
253
92
Perhaps you are referring to photon counting cameras, that can resolve single photon events? Neither CMOS nor CCDs are in general photon counters. CMOS and CCDs both record the photo-electric charge, but are read out differently. CCDs are read out by moving the charges row- or column-wise to the detector edge where they are A/D converted, while CMOS are A/D converted on site. This is the main reason why CMOS are so much faster at reading out.
"CMOS and CCDs both record the photo-electric charge" - so this is the reason why they are called analog devices? Because charge is a continuous value, not a discrete one (0 or 1).
 
  • Like
Reactions: Michael Clark

Kit.

EOS 6D MK II
Apr 25, 2011
1,265
682
"CMOS and CCDs both record the photo-electric charge" - so this is the reason why they are called analog devices? Because charge is a continuous value, not a discrete one (0 or 1).
As we can disregard number-phase uncertanty for photoelectrons, charge is a discrete value (a number of electrons). But counting electrons one by one is too slow for our goals, so the charge is measured by the voltage it creates on a given capacitor, and voltage is a continuous value.
 
  • Like
Reactions: Berowne

Berowne

... they sparkle still the right Promethean fire.
Jun 7, 2014
253
92
What bothers me is that in their "testing protocol" (https://www.dxomark.com/About/In-depth-measurements/DxOMark-testing-protocols/ISO-sensitivity) they don't specify the color temperature of their light source and even do explicitly mention LEDs. And then they also don't say what they do if the saturation of the different color channels happens at different exposures.
Kit, if i remember well, the exposure meter is sensitive to different colours (measures different values for different colours), but not the sensor. Anyway, if you take photos of a grey-card (18%), this should not matter at all.
 

Kit.

EOS 6D MK II
Apr 25, 2011
1,265
682
Kit, if i remember well, the exposure meter is sensitive to different colours (measures different values for different colours), but not the sensor. Anyway, if you take photos of a grey-card (18%), this should not matter at all.
The sensor has 3 color channels saturating with some degree of independence: the ones corresponding to R, G, and B color filters of its Bayer pattern. You don't just "take photos of a grey card", you take photos of a grey card that is illuminated by light of a particular spectrum. If it's a bluish light (high color temperature), the B channel would normally saturate at a lower exposure (and the R channel would normally saturate at a higher exposure) than if it were a reddish light (low color temperature). If it's a LED light, with spectrum vastly different from the spectrum of an incandescent source, both the R and the B channels can saturate before the G channel does.
 
  • Like
Reactions: Berowne

TAF

EOS RP
Feb 26, 2012
341
30
If you know your skills as well as your equipment, you will be successful in a thousand photographs.
If you know your skills but not your equipment, for every successful photograph, there will be a failure.
If you know neither your skills nor your equipment, use the green box setting...

with apologies to Sun Tzu
 
  • Like
Reactions: BeenThere

Pape

EOS RP
Dec 31, 2018
381
225
you dont need know how wheel works to drive with bicycle. Just jump to saddle and have fun :)
same goes with ISO i believe ? were it fake or not it reduces post editing job :)
 

TAF

EOS RP
Feb 26, 2012
341
30
Perhaps I am simply old (yet not even 60), but doesn't everyone use an 18% gray card and evaluate their new toy equipment to make certain they know how it really works before getting serious?

In the days of film, when I bought a new type of film, I would put a few 'known exposure' frames at the head of the roll and then follow the manufacturers instructions precisely, so that I would know how far it deviated from my expectations. I could then make appropriate adjustments, and I was all set. Since the film makers were VERY consistent within their own product, I rarely noticed any changes once I knew where I was.

But KODAK to Agfa to Fuji etc? And then within film types? Plenty of differences to account for.

At least our modern sensors don't change over time, at least not that I have noticed. Has anyone with a really early camera noticed any changes? We are exposing a silicon surface to light, which does cause changes on the microscopic level. And of course, the shutter could need eventually adjustment, but I haven't had a digital SLR that hasn't warranted upgrading within a short enough period of time (under 10 years so far) such that perhaps there isn't time for deterioration to set in.
 

Don Haines

Beware of cats with laser eyes!
Jun 4, 2012
8,129
1,650
Canada
Perhaps I am simply old (yet not even 60), but doesn't everyone use an 18% gray card and evaluate their new toy equipment to make certain they know how it really works before getting serious?

In the days of film, when I bought a new type of film, I would put a few 'known exposure' frames at the head of the roll and then follow the manufacturers instructions precisely, so that I would know how far it deviated from my expectations. I could then make appropriate adjustments, and I was all set.
HA!

You have no idea how many pictures I have of my Kodak colour card! :)

Shooting in RAW and the ability to adjust white balance in post (at least to me) has to be the greatest leap forward in shooting with digital.......
 

BeenThere

EOS 6D MK II
Sep 4, 2012
842
169
HA!

You have no idea how many pictures I have of my Kodak colour card! :)

Shooting in RAW and the ability to adjust white balance in post (at least to me) has to be the greatest leap forward in shooting with digital.......
Certainly one of the greatest. For me, instant gratification (not having to wait for film developing) would have to be the greatest leap forward of digital photography.
 
  • Like
Reactions: Click