Why 'more or less stopped using ISO'?

Started 7 months ago | Questions
l_d_allan
Senior MemberPosts: 2,198Gear list
Like?
Why 'more or less stopped using ISO'?
7 months ago

In a recent thread where the OP was about base ISO
What determines a sensors Base ISO?

I was unclear about the following posts ...

bobn2 wrote:

Iliah Borg wrote:

Bob, even with film ISO rating is not very useful, it is just some approximate guideline. It is even less useful with digital. You know that...

-- hide signature --

I do know that, Iliah. Personally, I've more or less stopped using ISO.

I'm in the category of "not knowing that" ... about digital ISO being less than not very useful. Please clarify.

  • Is this specifically about "iso-less sensors" like many Sony and Nikon cameras?
  • So for such cameras ... just leave ISO at the camera's base ISO (typically 100)?
  • ...
  • Or does this also applies to Canon DSLR's (which I don't think can be described as iso-less)
  • Or because modern DSLR's have so little noise that use of Auto-ISO is appropriate?
  • So bobn2 and Iliah aren't concerned about what ISO is picked by Auto-ISO?
 l_d_allan's gear list:l_d_allan's gear list
Panasonic Lumix DMC-TZ3 Panasonic Lumix DMC-FZ47 Canon PowerShot S110 Canon EOS 5D Mark II Canon EOS 600D +22 more
ANSWER:
This question has not been answered yet.
Mark Scott Abeln
Veteran MemberPosts: 3,921Gear list
Like?
Re: Why 'more or less stopped using ISO'?
In reply to l_d_allan, 7 months ago

l_d_allan wrote:

I'm in the category of "not knowing that" ... about digital ISO being less than not very useful. Please clarify.

  • Is this specifically about "iso-less sensors" like many Sony and Nikon cameras?
  • So for such cameras ... just leave ISO at the camera's base ISO (typically 100)?
  • ...
  • Or does this also applies to Canon DSLR's (which I don't think can be described as iso-less)
  • Or because modern DSLR's have so little noise that use of Auto-ISO is appropriate?
  • So bobn2 and Iliah aren't concerned about what ISO is picked by Auto-ISO?

Boosting ISO usually decreases the dynamic range of the image, for all brands of cameras, although this is greatly influenced by the characteristics of your camera. Choosing exposure to preserve highlights, at base ISO, often leaves enough dynamic range in the shadows, which can be selectively brightened in post processing.

I don’t always use this process for two reasons:

  • Laziness.
  • Inability, at the time of capture, to see precisely what tones have been preserved well. 
 Mark Scott Abeln's gear list:Mark Scott Abeln's gear list
Nikon D200 Nikon D7000 Nikon AF-S DX Nikkor 35mm f/1.8G Nikon AF Nikkor 50mm f/1.8D Rokinon 85mm F1.4
Reply   Reply with quote   Complain
Luke Kaven
Veteran MemberPosts: 5,142
Like?
Re: Why 'more or less stopped using ISO'?
In reply to l_d_allan, 7 months ago

l_d_allan wrote:

bobn2 wrote:

Iliah Borg wrote:

Bob, even with film ISO rating is not very useful, it is just some approximate guideline. It is even less useful with digital. You know that...

I do know that, Iliah. Personally, I've more or less stopped using ISO.

I'm in the category of "not knowing that" ... about digital ISO being less than not very useful. Please clarify.

  • Is this specifically about "iso-less sensors" like many Sony and Nikon cameras?
  • So for such cameras ... just leave ISO at the camera's base ISO (typically 100)?
  • ...
  • Or does this also applies to Canon DSLR's (which I don't think can be described as iso-less)
  • Or because modern DSLR's have so little noise that use of Auto-ISO is appropriate?
  • So bobn2 and Iliah aren't concerned about what ISO is picked by Auto-ISO?

The Sony Exmor family of sensors (used in, for example, the D3x/D800/D7000, Sony cams, Pentax K-5), by doing all processing on the sensor, much of it right around the photosite, reduces read noise such that read noise is near-optimal at base ISO.  Near optimal.

Among these, in the D800, there is apparently a slight measured noise advantage to using analog gain up to about ISO 1200.  But it is not a big advantage, and you could shoot at ISO 100 all day and all night if you choose.  Everywhere from ISO 1600 and up is done strictly using digital multiplication and no analog gain, and potential highlight bits are thrown away needlessly.  If you stay at ISO 1600, you can always defer on the decision to use gain for ... years if you wish.

The Canon cameras (at least the ones I know) are similar to the D3/D700, D3s.  These sensors route low-level sensor signals to outboard chips for amplification and A-to-D.  They are noise limited at low ISO settings.  I would use full-stop ISO settings in-camera for everything up to ISO 1600.  But everywhere from ISO 1600 and up, these cameras are basically linear, and you can top out your auto-ISO settings at ISO 1600 with some confidence.

Reply   Reply with quote   Complain
bobn2
Forum ProPosts: 30,003
Like?
Re: Why 'more or less stopped using ISO'?
In reply to l_d_allan, 7 months ago

l_d_allan wrote:

In a recent thread where the OP was about base ISO
What determines a sensors Base ISO?

I was unclear about the following posts ...

bobn2 wrote:

Iliah Borg wrote:

Bob, even with film ISO rating is not very useful, it is just some approximate guideline. It is even less useful with digital. You know that...

-- hide signature --

I do know that, Iliah. Personally, I've more or less stopped using ISO.

I'm in the category of "not knowing that" ... about digital ISO being less than not very useful. Please clarify.

  • Is this specifically about "iso-less sensors" like many Sony and Nikon cameras?
  • So for such cameras ... just leave ISO at the camera's base ISO (typically 100)?
  • ...
  • Or does this also applies to Canon DSLR's (which I don't think can be described as iso-less)
  • Or because modern DSLR's have so little noise that use of Auto-ISO is appropriate?
  • So bobn2 and Iliah aren't concerned about what ISO is picked by Auto-ISO?

The whole concept of 'ISO' is based around a methodology which says 'choose a processing regime' and then 'choose an exposure to match'. The implication is that the purpose of controlling exposure is to control output image brightness. If you are one who controls the processing after capture, for instance by processing from raw, then you don't want to control exposure to conrol brightness, you need to control it in order to capture the maximum scene information, then you process to get the required brightness. Since ISO is all about mapping from exposure to output image brightness, it isn't much use when you want to maximise capture information - then you need to use other methodologies for exposure control, which have become loosely wrapped up as 'ETTR' or 'ISOless'.

In any case, what you're trying to do is use all of the sensor's capture range for whatever is the luminosity range of the subject.

-- hide signature --

Bob

Reply   Reply with quote   Complain
xpatUSA
Senior MemberPosts: 3,255Gear list
Like?
Re: Why 'more or less stopped using ISO'?
In reply to bobn2, 7 months ago

bobn2 wrote:

The whole concept of 'ISO' is based around a methodology which says 'choose a processing regime' and then 'choose an exposure to match'. Since ISO is all about mapping from exposure to output image brightness, it isn't much use when you want to maximise capture information - then you need to use other methodologies for exposure control, which have become loosely wrapped up as 'ETTR' or 'ISOless'.

Quite so.

With my camera, if shoot a scene at ISO 100 and 1/100 sec and then at ISO 400 and 1/100 sec, the raw data is the same in each image. I guess that makes it a) an 'ISO-less' camera and b) a waste of time messing with the ISO 'knob'.

cheers . . .

-- hide signature --

Ted

 xpatUSA's gear list:xpatUSA's gear list
Sigma SD9 Sigma SD10 Sigma SD14 Panasonic Lumix DMC-GH1 +2 more
Reply   Reply with quote   Complain
edhannon
Senior MemberPosts: 1,287Gear list
Like?
Re: Why 'more or less stopped using ISO'?
In reply to xpatUSA, 7 months ago

Which cameras do not change the content of the raw file when you change ISO without changing exposure (f-stop & shutter speed)? All that I am familiar with change the brightness.

All of the discusions about using bzse ISO and brightening in PP only talk about the impact to noise. The arguement is that, since SNR does not get better with increased ISO with the ISO-less cameras, you a re better off doing brightening in PP.

This ignores the potential for posterization when you push in PP. The curve of ADU wrt exposure in stops is exponential. The curve is very flat in the shadows and steep in the highlights. When you push by more thsn a couple of stops you loose a lot of bit re solution.

IMHO the best approach is to expose with as much light as you can and use ISO brightening to bring the highlights up to just short of saturation.

-- hide signature --
 edhannon's gear list:edhannon's gear list
Canon EOS 40D Pentax K10D
Reply   Reply with quote   Complain
bobn2
Forum ProPosts: 30,003
Like?
Re: Why 'more or less stopped using ISO'?
In reply to edhannon, 7 months ago

edhannon wrote:

Which cameras do not change the content of the raw file when you change ISO without changing exposure (f-stop & shutter speed)? All that I am familiar with change the brightness.

All of the discusions about using bzse ISO and brightening in PP only talk about the impact to noise. The arguement is that, since SNR does not get better with increased ISO with the ISO-less cameras, you a re better off doing brightening in PP.

This ignores the potential for posterization when you push in PP. The curve of ADU wrt exposure in stops is exponential. The curve is very flat in the shadows and steep in the highlights. When you push by more thsn a couple of stops you loose a lot of bit re solution.

IMHO the best approach is to expose with as much light as you can and use ISO brightening to bring the highlights up to just short of saturation.

-- hide signature --

I like to distinguish between 'P' and 'PP'. The point is that you set up your processing to get the brightness you want, not that you process for the 'ISO normal' brightness and then brighten in post-processing. That way, you can't ever get 'posterisation' - the reason being that you are never using any 'bit resolution' that was not there in the first place. In fact, using the in camera gain (if your camera isn't 'ISOless' doesn't provide any more 'bit resolution' - all it does is shift the signal to use more significant bits, clear of the noise generated late in the digitisation chain, which can sometimes occupy as much as the three lower bits.

-- hide signature --

Bob

Reply   Reply with quote   Complain
xpatUSA
Senior MemberPosts: 3,255Gear list
Like?
Re: Why 'more or less stopped using ISO'?
In reply to edhannon, 7 months ago

edhannon wrote:

Which cameras do not change the content of the raw file when you change ISO without changing exposure (f-stop & shutter speed)?

Sigma SD9, SD10, SD 14 and maybe the other Sigmas. The camera firmware creates the raw file from the sensor analog outputs (all three of them). The ISO setting does not change the 'gain' between the sensor outputs of (SD9) 550mV and the three 12-bit ADC converters. The firmware does some scaling, noise reduction, linearization but only passes the user's ISO selection as metadata in the raw file.

All that I am familiar with change the brightness.

Then you are only familiar with cameras that mess around with the gain between the sensor and the ADC, if that is what is meant by 'change the brightness'?

-- hide signature --

A Statement passed without Proof carries little Weight
Ted

 xpatUSA's gear list:xpatUSA's gear list
Sigma SD9 Sigma SD10 Sigma SD14 Panasonic Lumix DMC-GH1 +2 more
Reply   Reply with quote   Complain
Iliah Borg
Forum ProPosts: 16,083
Like?
Re: Why 'more or less stopped using ISO'?
In reply to xpatUSA, 7 months ago

xpatUSA wrote:

edhannon wrote:

Which cameras do not change the content of the raw file when you change ISO without changing exposure (f-stop & shutter speed)?

Sigma SD9, SD10, SD 14 and maybe the other Sigmas.

All my "Merrill" Sigmas. Plus nearly all MF cameras, some Panasonic cameras for high ISO settings, some early Pentax cameras, etc. Maybe a good name for the method is "ISO by MakerNote tag".

-- hide signature --
Reply   Reply with quote   Complain
edhannon
Senior MemberPosts: 1,287Gear list
Like?
Re: Why 'more or less stopped using ISO'?
In reply to Iliah Borg, 7 months ago

There are three places that brightening can be applied:

  • With amplification between the sensor andq analog to digital conversion (e.g. Pentax *ist line)
  • By using more bits in the analosg to digital conversion than are used in raw output file then bit shifting in firmware (e.g. Pentax K10)
  • By processing the raw data either in camera or in the raw converter.

The last one uses cheaper hardware but results in loss of effective bit depth.

-- hide signature --
 edhannon's gear list:edhannon's gear list
Canon EOS 40D Pentax K10D
Reply   Reply with quote   Complain
Iliah Borg
Forum ProPosts: 16,083
Like?
Re: Why 'more or less stopped using ISO'?
In reply to edhannon, 7 months ago

Brightening can be applied only to an image. Raw is not an image.

-- hide signature --
Reply   Reply with quote   Complain
D Cox
Senior MemberPosts: 7,628
Like?
Re: Why 'more or less stopped using ISO'?
In reply to bobn2, 7 months ago

bobn2 wrote:

The whole concept of 'ISO' is based around a methodology which says 'choose a processing regime' and then 'choose an exposure to match'. The implication is that the purpose of controlling exposure is to control output image brightness. If you are one who controls the processing after capture, for instance by processing from raw, then you don't want to control exposure to conrol brightness, you need to control it in order to capture the maximum scene information, then you process to get the required brightness. Since ISO is all about mapping from exposure to output image brightness, it isn't much use when you want to maximise capture information - then you need to use other methodologies for exposure control, which have become loosely wrapped up as 'ETTR' or 'ISOless'.

In any case, what you're trying to do is use all of the sensor's capture range for whatever is the luminosity range of the subject.

The problem I see with ETTR is the very small and low resolution display of the histogram on an LCD screen. Even in Photoshop's Levels control, it is poor (they haven't updated the display since screens were all 640x480).

This makes it difficult to find the highlights.

A "zebra" display might help (I haven't tried one), but would it show clipping on small specular highlights ?

(By the way, why do you write "methodologies" when you mean "methods" ? )

Reply   Reply with quote   Complain
D Cox
Senior MemberPosts: 7,628
Like?
Re: Why 'more or less stopped using ISO'?
In reply to xpatUSA, 7 months ago

xpatUSA wrote:

bobn2 wrote:

The whole concept of 'ISO' is based around a methodology which says 'choose a processing regime' and then 'choose an exposure to match'. Since ISO is all about mapping from exposure to output image brightness, it isn't much use when you want to maximise capture information - then you need to use other methodologies for exposure control, which have become loosely wrapped up as 'ETTR' or 'ISOless'.

Quite so.

With my camera, if shoot a scene at ISO 100 and 1/100 sec and then at ISO 400 and 1/100 sec, the raw data is the same in each image. I guess that makes it a) an 'ISO-less' camera and b) a waste of time messing with the ISO 'knob'.

Is it completely identical, including the metadata ? I would expect the file header to include some indication for the raw converter telling it by how much to multiply the numbers.

Reply   Reply with quote   Complain
Iliah Borg
Forum ProPosts: 16,083
Like?
Re: Why 'more or less stopped using ISO'?
In reply to D Cox, 7 months ago

The problem I see with ETTR is the very small and low resolution display of the histogram on an LCD screen.

Histogram is not telling much. Part of the image is blown, ok, but what part? Is it important part or not? Histogram does not tell it.

-- hide signature --
Reply   Reply with quote   Complain
D Cox
Senior MemberPosts: 7,628
Like?
Re: Why 'more or less stopped using ISO'?
In reply to Iliah Borg, 7 months ago

Iliah Borg wrote:

Brightening can be applied only to an image. Raw is not an image.

A digital image (as opposed to a film or a print) is an array of numbers with X, Y coordinates representing brightness levels at each point. Usually there are three values for each point, for the three primary colours.

A raw image is also an array of numbers stating the values read by the sensor at each X, Y point.

It is just as much an image file as is a TIFF or a GIF. JPGs could be regarded as corrupted image files.

Reply   Reply with quote   Complain
Iliah Borg
Forum ProPosts: 16,083
Like?
Re: Why 'more or less stopped using ISO'?
In reply to D Cox, 7 months ago

D Cox wrote:

Iliah Borg wrote:

Brightening can be applied only to an image. Raw is not an image.

A digital image (as opposed to a film or a print) is an array of numbers with X, Y coordinates representing brightness levels at each point.

No, not brightness.

-- hide signature --
Reply   Reply with quote   Complain
edhannon
Senior MemberPosts: 1,287Gear list
Like?
Re: Why 'more or less stopped using ISO'?
In reply to D Cox, 7 months ago

The way I use ETTR is:

  • Determine through testing how many stops above the meter reading saturation of the first channel occurs. I do this by taking images of a gray card at various exposures and plotting the raw values of the three channels.
  • With this knowledge I spot meter the important highlights - the ones I need detail in.
  • I use Zone System to "place" important highlights below saturation.

Spectral highlights do not need to be placed below saturation - only those that I need to retain detail.

Note that I only do ETTR when I have a difficult subject brightness range and need the precision. Most of the time Av or Tv modes are adequate.

-- hide signature --
 edhannon's gear list:edhannon's gear list
Canon EOS 40D Pentax K10D
Reply   Reply with quote   Complain
xpatUSA
Senior MemberPosts: 3,255Gear list
Like?
Re: Why 'more or less stopped using ISO'?
In reply to D Cox, 7 months ago

D Cox wrote:

xpatUSA wrote:

With my camera, if shoot a scene at ISO 100 and 1/100 sec and then at ISO 400 and 1/100 sec, the raw data is the same in each image. I guess that makes it a) an 'ISO-less' camera and b) a waste of time messing with the ISO 'knob'.

Is it completely identical, including the metadata ? I would expect the file header to include some indication for the raw converter telling it by how much to multiply the numbers.

To paraphrase Bill Clinton "it all depends what the meaning of 'it' is"

Myself, I said 'raw data', not meta-data and not 'the file'.

-- hide signature --

Cheers,
Ted

 xpatUSA's gear list:xpatUSA's gear list
Sigma SD9 Sigma SD10 Sigma SD14 Panasonic Lumix DMC-GH1 +2 more
Reply   Reply with quote   Complain
jonas ar
Regular MemberPosts: 312
Like?
Re: Why 'more or less stopped using ISO'?
In reply to edhannon, 7 months ago

edhannon wrote:

The way I use ETTR is:

  • Determine through testing how many stops above the meter reading saturation of the first channel occurs. I do this by taking images of a gray card at various exposures and plotting the raw values of the three channels.
  • With this knowledge I spot meter the important highlights - the ones I need detail in.
  • I use Zone System to "place" important highlights below saturation.

Spectral highlights do not need to be placed below saturation - only those that I need to retain detail.

Note that I only do ETTR when I have a difficult subject brightness range and need the precision. Most of the time Av or Tv modes are adequate.

Would it not be much simpler to bracket the exposure and pick the appropriate one retrospectively?

Reply   Reply with quote   Complain
edhannon
Senior MemberPosts: 1,287Gear list
Like?
Re: Why 'more or less stopped using ISO'?
In reply to jonas ar, 7 months ago

Even with bracketing you need to determine a starting point and how many stops to bracket.

Starting point needs to be close to where highlights are just below saturation.

In difficult exposure situations I find it best to spot meter several areas and then plan the exposure.

I have not found bracketing that useful.

-- hide signature --
 edhannon's gear list:edhannon's gear list
Canon EOS 40D Pentax K10D
Reply   Reply with quote   Complain
Keyboard shortcuts:
FForum MMy threads