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Author Topic: ETTR vs ISO  (Read 23035 times)
dreed
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« on: May 23, 2013, 10:31:14 PM »
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ETTR is a mantra that I often see spouted on the Internet as the cure for better IQ and at ISO 100, it makes complete sense.

But if I'm at ISO 3200 (say) and shooting at 1/200 +1 EV, would I get better IQ if I shot at ISO 1600 and used 1/200 at +0 EV?

Or does this depend on the sensor?
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Tony Jay
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« Reply #1 on: May 23, 2013, 10:40:31 PM »
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As you say, at ISO 100 (or, in fact, base ISO) it makes sense.
If not at base ISO it is (non)sense...

Tony Jay
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ErikKaffehr
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« Reply #2 on: May 23, 2013, 11:42:47 PM »
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It depends on sensor, or more exactly signal readout electronics. But, it is really exposure that matters.


Sony sensors: Iso matters little
Canon: Better shadow noise when increasing ISO, but little difference in mid tones. My guess.
Nikon: Depends, D800, D600 use Sony sensor D4 is more like Canon

Best regards
Erik


ETTR is a mantra that I often see spouted on the Internet as the cure for better IQ and at ISO 100, it makes complete sense.

But if I'm at ISO 3200 (say) and shooting at 1/200 +1 EV, would I get better IQ if I shot at ISO 1600 and used 1/200 at +0 EV?

Or does this depend on the sensor?
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Ray
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« Reply #3 on: May 24, 2013, 01:54:33 AM »
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What a coincidence. I'm in the process of gradually reorganizing my images, and just yesterday came across some images stored on an old hard drive, of a test I'd conducted in April 2006 to satisfy myself that increasing ISO on a Canon 5D to create an ETTR, as opposed to underexposing at ISO 100, really did have a substantial benefit regards general image quality.

My first reaction on coming across these images was to junk them, because the information they provide is now 'old hat' for me, and also I didn't have the RAW images stored in the same folder. I'll probably discover them later on some other old hard drive.

Anyway, I decided to keep the conversions in my newly created 'Technical issues and Lens Tests" folder and have attached below a couple of comparisons crops.
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jrsforums
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« Reply #4 on: May 24, 2013, 02:10:58 AM »
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ETTR is a mantra that I often see spouted on the Internet as the cure for better IQ and at ISO 100, it makes complete sense.

But if I'm at ISO 3200 (say) and shooting at 1/200 +1 EV, would I get better IQ if I shot at ISO 1600 and used 1/200 at +0 EV?

Or does this depend on the sensor?

Dreed, this subject has been covered in quite a few threads over the last couple years.  The best summary I have seen came from ejmartin

http://www.luminous-landscape.com/forum/index.php?topic=56947.msg463071#msg463071

Quote
What is the appropriate mantra?  I would prefer "Maximize Exposure"; maximize subject to three constraints:

(1) maintaining needed DoF, which limits how much you can open up the aperture;
(2) freezing motion, which limits the exposure time;
(3) retaining highlight detail, by not clipping wanted highlight areas in any channel. 

Note that ISO is not part of exposure.  Exposure has only to do with aperture and shutter speed.  Maximizing exposure guarantees that one captures as many photons as possible subject to photographic constraints, and therefore optimizes S/N.

How does ISO enter?  It enters as a subsidiary aspect of optimizing S/N.  On many cameras (those with CCD sensors, and the newer Sony Exmor sensors), there is little or no advantage to raising the ISO, which aids point (3) -- leaving the ISO at a low value may leave the histogram "to the left" for your chosen exposure, it will give more highlight headroom but will not degrade S/N; such cameras can safely be operated at close to their lowest ISO (the precise optimal ISO depends on the details of a given camera design).  On the other hand, for many other CMOS sensor'd cameras, such as Canon's offerings, and Nikons with Nikon-designed CMOS sensors (D3/D700/D3s, for example), noise relative to exposure is improved by increasing the ISO; after you have maximized the exposure (ie by satisfying criteria (1) and (2)), you have a tradeoff to make for (3) -- raising the ISO lowers shadow noise (up to a camera-specific point of diminishing returns, usually about ISO 1600), therefore improving S/N, but reduces highlight headroom for your chosen exposure, so one has to decide how high the ISO can go and still keep wanted highlights unclipped. 

Anyway, the prescription is to set the exposure (shutter speed and aperture only) according to (1) and (2); back off the exposure if at base ISO and you are compromising (3).  If you are compromising (3) with your chosen exposure and you are not at base ISO, then you should have started with a lower ISO.  Afterward, depending on the specifics of the camera's noise profile, further optimization results from raising the ISO, up to the limit specified by (3), or the camera's ISO point of diminishing returns, whichever is arrived at first.

So, it's (almost) all about ME.     
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John
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« Reply #5 on: May 24, 2013, 06:23:43 AM »
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3 or 4 articles on ETTR on this site, http://chromasoft.blogspot.ca/2009/09/why-expose-to-right-is-just-plain-wrong.html

Schewe has a short article on it as well, http://schewephoto.com/ETTR/

Emil has an intensive article on his site, http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html, scroll down to the S/N and Exposure Decision section.
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digitaldog
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« Reply #6 on: May 24, 2013, 08:32:29 AM »
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ETTR is a mantra that I often see spouted on the Internet as the cure for better IQ and at ISO 100, it makes complete sense.

It does depend on the camera system. In this example, using a Canon 5DMII, a HIGHER ISO produces less noise due to ETTR:



ETTR is nothing more than Exposure 101, in this case for processing raw data in your converter (Exposure + Development). You still need to decide an appropriate shutter and what DOF you wish and how much light you can work with. ETTR is about optimal exposure, not over exposure. If you increase the signal data for less noise only to end up with camera shake or the incorrect DOF you desire, it's a waste! You have linear raw data (your neg), you need to test your camera system to uncover the ideal way to expose for that data which many call ETTR. It should just be called ideal exposure for the media (raw) which is quite different than ideal exposure for the camera generated JPEG. Then you have to test the development (normalize for ideal rendering from ETTR data). Again, exposure and photography 101 so to speak, just different equipment and data to work with.
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Andrew Rodney
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BJL
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« Reply #7 on: May 24, 2013, 09:07:50 AM »
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Dreed, this subject has been covered in quite a few threads over the last couple years.  The best summary I have seen came from ejmartin
http://www.luminous-landscape.com/forum/index.php?topic=56947.msg463071#msg463071
Agreed! The only thing that I can see being worth adding is details on how high it is worth pushing up the ISO speed setting on a particular camera before you stop gaining anything with noise and instead are just saving the effort of adjusting levels up in post-processing, but at the added risk of blowing highlights due to "ISO amplifier clipping" even when the photosites themselves were not overfilled.

Some answers seem to be:
  • With the combination of a CCD and a high quality ADC, as in DMF backs, there is no IQ benefit to increased "ISO amplification", because all the noise enters before the amplification.
  • With Canon's combination of CMOS sensors (with on-sensor ISO amplification?) and off-board ADC, there can be benefits all the way up to about ISO 1600; see Ray's post for example.
  • With recent Sony and Nikon system cameras, there can be some benefit to going one stop above base ISO speed, to about ISO 400, but no significant benefit beyond that.
  • Similarly with the current generation of micro Four Thirds sensors, there can be some benefit to going one or even two stops above base ISO setting, maybe to ISO 800, but not beyond.
I am sure that others in this forum can add quantitative details (and corrections), based on all the testing that has been reported in other discussions here.
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BJL
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« Reply #8 on: May 24, 2013, 09:19:02 AM »
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That article is mostly rather silly, with all its comparisons at higher ISO settings and between images taken at different ISO setting. In the end it almost entirely contradicts its link-bait "completely wrong" headline with this
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there is one situation where ETTR can help - when you're already at the lowest ISO setting you camera offers
and this
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Bottom line - ETTR offers improved image quality in only one specific situation - where you can use a lower ISO setting than your camera has. In all other situations, ETTR will only ever decrease image quality.
But working at base ISO speed is a key part of the "classic ETTR" as described by Michael Reichmann in the article that this article quotes, so the bottom line is to agree that ETTR as originally described and advocated by Michael Reichmann (and Thomas Knoll?) is a good approach! All the rest is a straw man argument.
« Last Edit: May 24, 2013, 09:31:04 AM by BJL » Logged
jrsforums
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« Reply #9 on: May 24, 2013, 09:29:18 AM »
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Agreed! The only thing that I can see being worth adding is details on how high it is worth pushing up the ISO speed setting on a particular camera before you stop gaining anything with noise and instead are just saving the effort of adjusting levels up in post-processing, but at the added risk of blowing highlights due to "ISO amplifier clipping" even when the photosites themselves were not overfilled.

Some answers seem to be:
  • With the combination of a CCD and a high quality ADC, as in DMF backs, there is no IQ benefit to increased "ISO amplification", because all the noise enters before the amplification.
  • With Canon's combination of CMOS sensors (with on-sensor ISO amplification?) and off-board ADC, there can be benefits all the way up to about ISO 1600; see Ray's post for example.
  • With recent Sony and Nikon system cameras, there can be some benefit to going one stop above base ISO speed, to about ISO 400, but no significant benefit beyond that.
  • Similarly with the current generation of micro Four Thirds sensors, there can be some benefit to going one or even two stops above base ISO setting, maybe to ISO 800, but not beyond.
I am sure that others in this forum can add quantitative details (and corrections), based on all the testing that has been reported in other discussions here.

As I remember, I believe it was Emil who "tied" the increased ISO capability to the DxoMark DR curve.  That is, as long as the DR curve was relatively flat, you could get some ETTR gain from increased ISO.

In the chart below you can see your examples of the 5D3 and MFT sensors and the Sony sensor in the D800.
« Last Edit: May 24, 2013, 09:30:49 AM by jrsforums » Logged

John
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« Reply #10 on: May 24, 2013, 09:33:05 AM »
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That article is mostly rather silly, with all its comparisons at higher ISO settings and between images taken at different ISO setting. In the end it almost entirely contradicts its link-bait "completely wrong" headline with thisand thisBut working at base ISO speed is a key part of the "classic ETTR" as described by Michael Reichmann in the article that this article quotes, so the bottom line is to agree that ETTR as originally described and advocated by Michael Reichmann (and Thomas Knoll?) is a good approach! All the rest is a straw man argument.

BJL...The articles major focus seemed to be on ISO benefit (or lack of) for ETTR.  Unfortunately the camera used was a Canon G10, which is CCD....so in Emil's terms....ISO-less.
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« Reply #11 on: May 24, 2013, 09:42:26 AM »
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@jrsforums thanks for the graphs. My understanding of the math of it is that there is no further benefit once the curve hits the straight line "one stop per stop" slope section at right. So, unravelling the misguided and confusing horizontal axis shift on those graphs, the rule seems to be:
  • D800: no significant IQ benefit to increasing ISO setting (with same shutter speed and f-stop)
  • E-M5: worth going one stop, to the ISO 400 setting (I think due to having 12-bit ADC rather than 14.)
  • 5D Mk 3: worth going as far as the ISO 1600 setting, and maybe even 3200
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RFPhotography
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« Reply #12 on: May 24, 2013, 10:03:02 AM »
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That article is mostly rather silly, with all its comparisons at higher ISO settings and between images taken at different ISO setting. In the end it almost entirely contradicts its link-bait "completely wrong" headline

Don't agree.  What he's doing is showing why ETTR doesn't apply at higher ISO settings with many cameras.  Basically, cameras with sensor response like the D7000 and Pentax K5 - I think those were the first well-known about 'ISOless' sensors don't benefit from ETTR at other than base ISO.  Some other cameras, that have a more curved response will benefit, to a point, using ETTR at higher than base ISO.  But even in those cameras, after a point there is no longer a benefit because the response becomes like those with 'ISOless' sensors.  I'm not completely convinced by his hue twist argument but the ISO comparisons are valid.

Quote
But working at base ISO speed is a key part of the "classic ETTR" as described by Michael Reichmann in the article that this article quotes, so the bottom line is to agree that ETTR as originally described and advocated by Michael Reichmann (and Thomas Knoll?) is a good approach! All the rest is a straw man argument.

Neither the original article from 2003 nor the updated article from 2011 mention shooting at base ISO.  I just looked at both again and didn't see anything about base ISO. 

The problem with the 'ETTR Mantra' is that there are some who will claim that ETTR is the only way to shoot in all circumstances.  That's simply not the case.  That's what the Chromasoft articles point out and, if I recall, I think Schewe's article talks about using base ISO (would have to go back and reread to be sure).
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digitaldog
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« Reply #13 on: May 24, 2013, 10:42:49 AM »
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  • 5D Mk 3: worth going as far as the ISO 1600 setting, and maybe even 3200
According to Eric Chan, if you shoot Raw, there’s no reason to shoot above ISO3200 on the 5DMII, not sure about the III. The noise levels will either be the same or might actually be worse if you don’t simply pin the max at ISO 3200 and adjust that Raw using the Exposure slider in ACR. ISO’s above 3200 are only useful for 5DMII users shooting JPEGs. That was back when we were using PV2003/2010 but I don't know that PV2012 would make that any different.

Quote
That article is mostly rather silly,
I agree!
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Andrew Rodney
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« Reply #14 on: May 24, 2013, 10:46:51 AM »
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The problem with the 'ETTR Mantra' is that there are some who will claim that ETTR is the only way to shoot in all circumstances.  That's simply not the case.  That's what the Chromasoft articles point out and, if I recall, I think Schewe's article talks about using base ISO (would have to go back and reread to be sure).

It's only a problem when the photographer doesn’t understand the basics of exposure and the role it plays on other aspects of photography which I mentioned (ETTR that causes camera shake, undesired DOF etc). Otherwise ETTR is simply an attempt at producing the best quality data. In the old days, we could pop ISO 100 film OR ISO 800 film based on what we knew or thought we knew about exposing a scene. We used ISO 100 when we knew we wanted lower noise (grain) than ISO 800 and we had abundant light to produce the desired results (san's camera shake etc). IF you have enough light, why would you not setup the camera system to provide the most noise free image? Then you can go out and buy a plug-in that adds noise to look like film <g>.
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Andrew Rodney
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« Reply #15 on: May 24, 2013, 10:57:57 AM »
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Fair enough: the article by MR does not explicitly talk about working at base ISO; it is just that in the context of what MR has said elsewhere on the same site, I tend to take it as "so obvious as to not need stating" that the first step to improving IQ is to use the lowest viable ISO setting, before moving on to refinements like ETTR.

Rather than debate his blatantly exaggerated "just plain wrong" criticism, based mostly on the inadequate example of a now almost irrelevant CCD sensor, let me just restate what might in the end be points of agreement:

  • Many people misapply the ETTR concept at higher than base ISO settings. (C.f. my criticism of DxO's ISO speed calibration.)
  • When one can use base ISO speed, the "ETTR" strategy of increasing exposure to just below highlight clipping can sometimes give better results than an exposure that places the mid-tones normally. The main case is when one can use an Exposure Index lower than the base ISO speed setting, due to a relatively small gap between midtones and brightest highlights, and with CCD's and most non-Canon CMOS sensors, this might often be achieved more easily by using the special "low ISO" settings.
  • With some CMOS sensors (mostly Canon these days), there can also be an advantage to increasing ISO speed with the same exposure level (same shutter speed and aperture ratio) until the ADC output level histogram is "at the right".
  • As MR notes in followups to his original article, the preview histograms that cameras give us, based on a JPEG preview, are not ideal. For example, on many cameras, that preview shows clipping one or more stops before there is any clipping of raw data. So optimal ETTR can involve being willing to push exposure a bit into "highlight red-lining".
  • Auto-bracketing of exposure might be a far easier approach for most people most of the time!
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digitaldog
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« Reply #16 on: May 24, 2013, 11:04:35 AM »
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Fair enough: the article by MR does not explicitly talk about working at base ISO; it is just that in the context of what MR has said elsewhere on the same site, I tend to take it as "so obvious as to not need stating" that the first step to improving IQ is to use the lowest viable ISO setting, before moving on to refinements like ETTR.

But it's not obvious as I tried to illustrate with the Canon. A higher ISO produces less noise than a lower one (again, due to ETTR).

Quote
- as MR notes in followups to his original article, the preview histograms that cameras give us, based on a JPEG preview, are not ideal. For example, on many cameras, that preview shows clipping one or more stops before there is any clipping of raw data. So optimal ETTR can involve being willing to push exposure a bit into "highlight red-lining".
We had no such LCD on film cameras yet many photographers learned to expose properly (ideally) for their film and development and didn't take any ISO setting at face value. ETTR is just ideal exposure for raw data. That the camera LCD is lying to us just forces us to learn to expose as we all did prior to digital capture. IF you capture raw data and use the LCD as your guide, you are basically under exposing that data which isn't ideal exposure. Just as we could under expose film and push it (to a degree), it wasn't considered an ideal exposure and development process.
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Andrew Rodney
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jrsforums
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« Reply #17 on: May 24, 2013, 11:52:38 AM »
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We had no such LCD on film cameras yet many photographers learned to expose properly (ideally) for their film and development and didn't take any ISO setting at face value. ETTR is just ideal exposure for raw data. That the camera LCD is lying to us just forces us to learn to expose as we all did prior to digital capture. IF you capture raw data and use the LCD as your guide, you are basically under exposing that data which isn't ideal exposure. Just as we could under expose film and push it (to a degree), it wasn't considered an ideal exposure and development process.

I agree...sorta.

Just like with film, we can "calibrate" our results, so we "know' how to "get it right in the camera"....which means optimally exposed....which is different by media...whether it is different film stocks, digital jpeg, or RAWs from different digital sensors.

Doing my own testing with RawDigger, I found, for the 5D3, that I could spot meter the highest significant highlight and then place it at +3 to +3.5 stops over metered.  This gave me an image exposed as far to the right as possible, without any channels clipped.

Jim Kasson, on his blog, The Last Word, did a lot of testing on different cameras...many which did not have spot meters, to arrive at means to adjust the histogram to more closely mimic a RAW histogram.
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John
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« Reply #18 on: May 24, 2013, 11:54:19 AM »
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It does depend on the camera system. In this example, using a Canon 5DMII, a HIGHER ISO produces less noise due to ETTR:



ETTR is nothing more than Exposure 101, in this case for processing raw data in your converter (Exposure + Development). You still need to decide an appropriate shutter and what DOF you wish and how much light you can work with. ETTR is about optimal exposure, not over exposure. If you increase the signal data for less noise only to end up with camera shake or the incorrect DOF you desire, it's a waste! You have linear raw data (your neg), you need to test your camera system to uncover the ideal way to expose for that data which many call ETTR. It should just be called ideal exposure for the media (raw) which is quite different than ideal exposure for the camera generated JPEG. Then you have to test the development (normalize for ideal rendering from ETTR data). Again, exposure and photography 101 so to speak, just different equipment and data to work with.

In this example, the exposure (if I read the exposure data properly--it is somewhat blurred) is the same: 1/60 sec @ f/5.6. As Emil states:

"Note that ISO is not part of exposure.  Exposure has only to do with aperture and shutter speed.  Maximizing exposure guarantees that one captures as many photons as possible subject to photographic constraints, and therefore optimizes S/N."


In the case of the Canon used here, increasing the ISO will give a better looking histogram, but the real reason for increasing the ISO in this case is to reduce the read noise. Photon noise will be unchanged, since the number of photons collected is the same. With an ISO-less sensor, one could leave the ISO setting at base and increase exposure with the raw converter and get the same results, while providing more highlight headroom.

Bill
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digitaldog
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« Reply #19 on: May 24, 2013, 12:10:56 PM »
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In this example, the exposure (if I read the exposure data properly--it is somewhat blurred) is the same: 1/60 sec @ f/5.6.

Yes. Exposure settings for aperture and shutter are identical, the only difference is the ISO setting. And the differences in the amount of noise is significant as one would expect with ETTR (optimal exposure for raw).


Quote
As Emil states:

"Note that ISO is not part of exposure.  Exposure has only to do with aperture and shutter speed.  Maximizing exposure guarantees that one captures as many photons as possible subject to photographic constraints, and therefore optimizes S/N."


In the case of the Canon used here, increasing the ISO will give a better looking histogram, but the real reason for increasing the ISO in this case is to reduce the read noise. Photon noise will be unchanged, since the number of photons collected is the same. With an ISO-less sensor, one could leave the ISO setting at base and increase exposure with the raw converter and get the same results, while providing more highlight headroom.

I don't care about the Histogram! But what I see is a vast difference in noise whereby the ONLY setting change is ISO. So it's obviously affecting the degree of noise.

You saying increasing the ISO in this case is to reduce the read noise, this isn't also ETTR? Seems the number of photons collected should be the same since what he's calling exposure is fixed in both examples. The results however are clear in terms of the differences in noise and I understand that not all camera sensors respond as this Canon does.
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Andrew Rodney
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