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Author Topic: ETTR vs ISO  (Read 20010 times)
digitaldog
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« Reply #40 on: May 24, 2013, 02:27:26 PM »
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The exposures are the same, so how do you call the shot at higher ISO as optimal exposure for raw?
The combo of setting provided a superior capture. ISO has no role here? I have to at the very least enter some value for the meter.
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The appellation "ETTR" implies that the histogram is a determining factor and the histogram gives some indication of the number of photons collected only at base ISO. Certainly, at any ISO it is not wise to leave space at the right of the histogram is one is interested in the best SNR.
Where and why does ETTR have to do anything with a Histogram? Which Histogram? In the raw processor (which is now part of the development process)? On the camera (not useful)?
In my mind, ETTR is using the various tools and settings we have to produce the optimal capture data. I don't see how the Histogram is even necessary expect to understand you didn't expose to the right enough or you exposed too far and you clipped. You could find this out without a Histogram too.
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I wouldn't call it exposure to the right, since the exposure is the same in both instances. However, this is all semantics and the important point it to obtain maximal image quality.
Yes it's semantics but that's all we have at this point. Maybe ETTR is the wrong term. Expose to the right of an incorrect histogram? How about just Expose Optimally? Expose to right implies that there's this 'recommended' exposure but that's 'wrong' so adjust everything over (to the right). The recommendation prior to moving to the right is incorrect in terms of an ideal exposure, would you agree? If so, ETTR probably is the wrong term and I think most agree, it is confusing to a lot of users. They think they are over exposing when they are simply exposing optimally and not using the recommendation of a meter that's been designed for film and later, a JPEG. IF one tests where the sensor clips data they wish to capture, and move a tad to the left, would this not be correct and further ideal exposure? Maybe the term should be ETTL (after you figure out what not to clip).
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« Reply #41 on: May 24, 2013, 02:39:55 PM »
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This entire ETTR, exposure, ISO, testing takes me back to the mid 1980's while at photo school. I think 2nd trimester, we had one of our first assignments shooting color (first trimester we only shot 4x5 B&W film, it could not be burned or dodged in the darkroom for any assignment). This new color assignment was to shoot 4x5 color neg, I think it was Kodak VPS II or something. Stated ISO 160 on the box. The subject had to be stationary and have an 18% gray card in the center filling up at least 20%. We were to shoot at the recommended ISO, then 1, 2 and 3 stops under and over. We processed all the film together. Then in the darkroom, we had to make prints whereby the gray card on the print matched the actual gray card. Once all 7 prints were mounted and viewed, the results were very surprising! The plus 1 and 2 stops were easily printable and both produced a better print quality than the "normal" ISO 160 image. The under exposed prints all suffered compared to the 'normal' exposure.

ISO 160 for VPS worked just fine! But rating it at ISO 80 (or 40) and treating the rest of the process the same produced a very visible and beneficial result! No Histograms. But we did expose to the right if you will.
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« Reply #42 on: May 24, 2013, 02:56:30 PM »
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Where and why does ETTR have to do anything with a Histogram?
The very phrase "Expose To The Right" seems to originate in Michael Reichmann's article Expose (to the) Right, and refers to a strategy that is explicitly involved the camera's preview histogram:
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The simple lesson to be learned from this is to bias your exposures so that the histogram is snugged up to the right, but not to the point that the highlights are blown.

So at the risk of getting into a semantic debate, I agree that for what you are talking about with external meters and such,
[Maybe] ETTR is the wrong term.
Maybe your point is just the advantages of exposing for the highlights, and the possible advantage (mostly with Canon sensors) of pushing the analog gain (ISO) as high as possible without producing amplifier clipping (at least up to about ISO 1600 or 3200).
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jrsforums
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« Reply #43 on: May 24, 2013, 03:00:57 PM »
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Hi John,

Jim Kasson devised an illustrative way to determine the maximum useful ISO setting, beyond which it is better to just underexpose and boost with the Raw converter's exposure setting.

See the attachment where I used a similar method to determine it for my camera.

Cheers,
Bart

Thanks, Bart

I must have missed that thread.  Only had seen Jim's work from his blog.  From the length of the thread, I got a lot of reading to do :-)  ....and some testing...
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« Reply #44 on: May 24, 2013, 03:35:33 PM »
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I have mentioned Jim Kasson's series of blog posts on ETTR and using in-camera histograms.  For those interested, here is a link to them:
http://blog.kasson.com/?page_id=2387

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« Reply #45 on: May 24, 2013, 03:46:42 PM »
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i had discussed with Jim my method of using the 5D3's built in 1.5% spot meter to place the significant highlight.

He did not have a 5D3, but did test with a hand held spot meter.  His results are here:
http://blog.kasson.com/?p=2215

Even using this method, I still use the histogram to make sure the shadows are includd and no bracketing is required.  If bracketing is required, I use the spot meter to capture the highlights in the first shot and subsequent shots are +EC to capture the shadows.

I do believe the histogram is a tool to use, unfortunately it does not give true readings of the RAW image.  However, using this or other methods Jim tested (and have been written up other places) one can, using Emil's term, Maximize Exposure...and it can be done mostly without external tools, handheld meters, etc.,  of the bygone film era.
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« Reply #46 on: May 24, 2013, 03:53:49 PM »
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Jim Kasson devised an illustrative way to determine the maximum useful ISO setting, beyond which it is better to just underexpose and boost with the Raw converter's exposure setting.

Thanks, Bart. After working with the photon-compensated SNR curves for a while, I now believe that they ought to be used in conjunction with the Unity-Gain ISO to determine the point where you should stop turning up the ISO and start using the Exposure control in your favorite raw developer instead. Conventional UG ISO wisdom is that you should stop turning up the ISO a stop or two above the UG ISO. The photon-compensated SNR curves usually, but not always, bear that out. I'll show some examples further on in this post.

There's one other ISO you should consider: it's the one where your camera just throws in the towel and stops increasing the analog gain between the sensor and the analog-to-digital converter (ADC) and starts shifting the data to the left, first by one bit, and then, as the ISO goes up, by more. You certainly don't want to crank the ISO up past that point, unless you can't see the image in the back of the camera when you're chimping.

How do you find out when your camera stops amplifying more and starts shifting bits? The easiest way is to take a series of pictures of a featureless subject exposed per meter across a range of ISOs, and bring the raw data into RawDigger, and look at the histograms. When every other bucket is empty, the camera has shifted the data one bit-position to the left.

If you're new to Unity-Gain ISO, here's a place to start, and a method to find out what the UG ISO of your camera is.

OK, now for the examples. Here's one for a Nikon D4:



As you can see, the D4 is essentially ISO-less until about 3200, which is about 2 stops above the UG ISO. Both US ISO and SNR agree that you shouldn't use ISOs above 3200 unless you have some special reason. Up to ISO 6400, the D4 does no bit shifting.

 
With the D800E, the situation is similar:



Above ISO 1600, a little over two stops above the UG ISO, the SNR starts to degrade. At ISO 3200, the D800E becomes a 13-bit camera, and turns into a 12-bit camera at ISO 6400. Best to stop at 1600. A friend who is into astrophotgraphy did extensive subjective testing with his D800E and decided that you shouldn't go any higher than 1250.

With the Sony RX-1, here's the situation:



The reason for the two UG ISO arrows is that, although Sony advertises the RX-1 as a 14-bit camera, my copy has every other histogram bucket empty, indicating that it's really a 13-bit camera. The SNR curves show that less than two stops above the 13-bit UG ISO, the party is pretty much over. Up to ISO 6400, the RX-1 does no bit shifting.

With the Sony NEX-7, the curves look like this:



These curves give a different result from the ones above with respect to UG ISO. They indicate that you shouldn't use the NEX-7 above its UG ISO. Because the NEX7 is a 12-bit camera, the UG ISO is two stops higher than it would be if it were a 14-bit camera. If it were a 14-bit camera, the two-stops-above-UGISO rule would apply.

Now for something completely different. Here are the curves for a camera with a non-Sony sensor. In fact, the sensor in the Leica M9 isn't even a CMOS sensor:



We see dramatic reductions in SNR above 640, which is about a stop and a half abouve the UG ISO. The M9 does no bit shifting.

I don't have results for any Canons, and I have been told that they do better than the five cameras for which I've shown data here as the ISO increases.

Jim
« Last Edit: May 24, 2013, 04:23:32 PM by Jim Kasson » Logged

bjanes
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« Reply #47 on: May 24, 2013, 04:58:33 PM »
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The combo of setting provided a superior capture. ISO has no role here? I have to at the very least enter some value for the meter. Where and why does ETTR have to do anything with a Histogram? Which Histogram? In the raw processor (which is now part of the development process)? On the camera (not useful)?

ISO does have a role, but as Emil points out here, ISO is not exposure. He explains it better than I can and with more authority, so why don't you go to the link and read up on the matter?

The histogram that one uses when actually deciding on exposure in the field is the camera histogram. You could ask Michael what he meant by ETTR, but I think he was using the camera histogram to set ETTR exposure, hence the term right refers to the appearance of that histogram. The camera histogram is useful if you now how to use it and have done your homework with Rawdigger. Jim Kasson has some useful tips. One can also use UniWB to get an approximation of the raw histogram. The ACR/LR histogram has problems, since it uses a baseline exposure. Also, PV2012 has image adaptive exposure and tends not to clip highlights. RawTherapee does have a raw histogram available with the click of the mouse.

In my mind, ETTR is using the various tools and settings we have to produce the optimal capture data. I don't see how the Histogram is even necessary expect to understand you didn't expose to the right enough or you exposed too far and you clipped. You could find this out without a Histogram too. Yes it's semantics but that's all we have at this point. Maybe ETTR is the wrong term. Expose to the right of an incorrect histogram? How about just Expose Optimally? Expose to right implies that there's this 'recommended' exposure but that's 'wrong' so adjust everything over (to the right). The recommendation prior to moving to the right is incorrect in terms of an ideal exposure, would you agree? If so, ETTR probably is the wrong term and I think most agree, it is confusing to a lot of users. They think they are over exposing when they are simply exposing optimally and not using the recommendation of a meter that's been designed for film and later, a JPEG. IF one tests where the sensor clips data they wish to capture, and move a tad to the left, would this not be correct and further ideal exposure? Maybe the term should be ETTL (after you figure out what not to clip).

I agree. However, the term ETTR does imply the use of a histogram and this leads to confusion. What do you think right is referring to? Nevertheless, a properly interpreted histogram is helpful at base ISO. Measuring the highlight reading with a spot meter where the sensor saturates is a good method, but then you have to determine the location in the scene where the brightest highlight you don't want to clip is, take the reading with a 1 degree spot meter, and transfer it to the camera. When you do all this you may miss action in other than a static scene. The spot metering on the camera is often does not have a sufficiently narrow angle of view.

With today's high performance sensors such as the Sony Exmoor, ETTR is less important than it used to be and it is often more expeditious to use matrix metering and adjust the exposure if the camera histogram is too far to the left. However, bit of highlight headroom is sometimes advisable and one can make corrections with the raw converter. Remember that SNR varies with the square root of the exposure, so underexposing by one whole stop (not advisable in most situations) reduces the SNR by only a factor of sqrt(2).

Bill
« Last Edit: May 24, 2013, 05:09:29 PM by bjanes » Logged
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« Reply #48 on: May 24, 2013, 05:50:12 PM »
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ISO is part of exposure.  Emil hints at in in his response linked above.  He says that the idea is to maximise exposure within the constraints of DOF and the shutter speed necessary for the situation.  Depending on the shooting circumstances, ISO has to be taken into consideration and, thus, is part of exposure.  At least insofar as the response of the sensor is concerned.  But also with respect to the needs of the photographer and the ability to post-process.

Shooting, for example, fast moving sports like hockey or motor racing requires faster shutter speeds to get the necessary action-stopping movement.  PJs shooting in these conditions don't have the luxury of time to fiddle with sliders in post.  They shoot and fire the images off to their publication or agency in order to get the pics in the public eye as quickly as possible.  A little extra noise isn't of significant concern so hiking up the ISO to get the required shutter speed for a 'normal' exposure is what will be done; as opposed to shooting at base ISO and screwing around in post while the competition is getting images onto the web for distribution or the competing newspaper is getting a jump on a story.  This doesn't apply just to sports, of course, but any situation where conditions merit cranking the ISO to get a 'normal' exposure.
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« Reply #49 on: May 24, 2013, 06:10:44 PM »
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ISO is part of exposure.  Emil hints at in in his response linked above.  He says that the idea is to maximise exposure within the constraints of DOF and the shutter speed necessary for the situation.  Depending on the shooting circumstances, ISO has to be taken into consideration and, thus, is part of exposure.  At least insofar as the response of the sensor is concerned.  But also with respect to the needs of the photographer and the ability to post-process.

Shooting, for example, fast moving sports like hockey or motor racing requires faster shutter speeds to get the necessary action-stopping movement.  PJs shooting in these conditions don't have the luxury of time to fiddle with sliders in post.  They shoot and fire the images off to their publication or agency in order to get the pics in the public eye as quickly as possible.  A little extra noise isn't of significant concern so hiking up the ISO to get the required shutter speed for a 'normal' exposure is what will be done; as opposed to shooting at base ISO and screwing around in post while the competition is getting images onto the web for distribution or the competing newspaper is getting a jump on a story.  This doesn't apply just to sports, of course, but any situation where conditions merit cranking the ISO to get a 'normal' exposure.

Please reread Emil's quote on the mantra "Maximize Exposure" in Reply#4 above.  I think it takes in all the conditions you mention.  If ISO must be raised to get the aperture and shutter speed you need, that's it....they are the first consideration.

...but exposure, per Emil, is the amount of light reaching the sensor.  Increasing ISO does not increase exposure, it increase the amplification of the signal.
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« Reply #50 on: May 24, 2013, 06:19:58 PM »
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ISO is part of exposure. 
Agreed, has to be (part).

bjanes:
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ISO does have a role, but as Emil points out here, ISO is not exposure.
So if I set exposure then ISO, no change? Doesn't seem that way. It plays a role, always has. Let's put it this way, exposure and ISO have to both be under equal consideration. Or... exposure without any recognition of ISO is hard!

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However, the term ETTR does imply the use of a histogram and this leads to confusion.
Seems that way if we are to interpret ETTR to mean Expose to the Right of the incorrect camera Histogram. I'd prefer we call it ER (Expose Right). Or ERFR (Expose Right For Raw). IF we had a true raw histogram we'd be foolish to ETTR. But my point is we don't need a histogram, we never did to expose right. It be great if we could use one that actually showed us the real data. I guess I'm old school. I've spent more years properly exposing film than shooting digital and old habits die hard. I question why I'd look at a Histogram that's flat out wrong, then expose to it's right instead of testing the sensor and exposure/development then get the correct exposure without looking at incorrect information.

If I could start over again, I'd prefer not to use ETTR but rather tell people that for raw capture, the current histogram is a hack. Use tools and techniques to expose right just as we did prior to the first camera histogram. Just as we did with film after testing. IOW, base ISO 100 for JPEG may very well be IOS 25 and it is easy to adjust for this when exposing. Just as I did with the color neg film (san's histogram <g>).

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Nevertheless, a properly interpreted histogram is helpful at base ISO.
Agreed, now all we need is the properly displayed histogram because interpretation on the one provided isn't close to an exact science.

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With today's high performance sensors such as the Sony Exmoor, ETTR is less important than it used to be
I'm sure that's true but I'd hate to suggest that due to this, we can and should be sloppy with exposure. Wasn't the case years ago when we shot transparency although we had some tricks: Snip tests, push/pull processing (more than ˝ a stop, you messed up), Polaroids (and back to interpretation), fill an A12 back with a roll and shoot 12 test shots, no snip tests etc. I suppose with digital, we can be far more off on exposure unlike chrome but that isn't ideal. But if you're shooting street scenes or animals at the zoo, getting a half decent exposure is fine. In a studio setup or controlled situations, I'd prefer to nail exposure because there's no reason not to.
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« Reply #51 on: May 24, 2013, 06:26:24 PM »
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Please reread Emil's quote on the mantra "Maximize Exposure" in Reply#4 above.  I think it takes in all the conditions you mention.  If ISO must be raised to get the aperture and shutter speed you need, that's it....they are the first consideration.

Absolutely agree! Lower ISO to reduce noise that add's camera shake isn't a good move! Just as in the old days, if we expected a lot of light, got the scene and found we had to replace the ISO 100 transparency for ISO 400 (despite more grain), we did so. This again is all photography 101. We're a bit spoiled that we can dial in any ISO, capture by capture as we wish. A noise free but blurry image isn't something most people desire. Sharp and a bit of grain, far better IMHO.

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...but exposure, per Emil, is the amount of light reaching the sensor.  Increasing ISO does not increase exposure, it increase the amplification of the signal.

The net results are what's important. The ISO on a camera and the ISO rated on film (which can be wrong) should not be considered 100% identical or on parity should they? What if instead of calling the dial ISO it was named something else, would not altering the settings alter the results (and exposure)? More semantics. Can we really separate ISO from exposure when making a capture? If I use ISO 100 film and push it 1 stop, but shoot another roll at ISO 100 and process it normal, don't we expect to see a difference in the two rolls of film (all else being equal)? Same amount of light hit the film.
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« Reply #52 on: May 24, 2013, 07:12:17 PM »
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.

The net results are what's important. The ISO on a camera and the ISO rated on film (which can be wrong) should not be considered 100% identical or on parity should they? What if instead of calling the dial ISO it was named something else, would not altering the settings alter the results (and exposure)? More semantics. Can we really separate ISO from exposure when making a capture? If I use ISO 100 film and push it 1 stop, but shoot another roll at ISO 100 and process it normal, don't we expect to see a difference in the two rolls of film (all else being equal)? Same amount of light hit the film.

The net results are important....but you have to understand the perspective

For a photographer, the exposure net result includes the consideration of ISO.

For the sensor scientist, the exposure net result is ONLY the light hitting the sensor, which does not include ISO. 

This is important to understand for CCD and Exmor where the sensors are called ISOless, because you will not get any result from increasing ISO in camera than you can get in the RAW conversion.  In these cases, ISO for the photographer becomes the same as the sensor scientist...meaningless...except for the jpeg he sees in the LCD on the back of the camera.

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« Reply #53 on: May 24, 2013, 07:15:31 PM »
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For a photographer, the exposure net result includes the consideration of ISO.
Agreed!

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For the sensor scientist, the exposure net result is ONLY the light hitting the sensor, which does not include ISO.  
I'm not a scientist (sensor or otherwise), don't even play one on TV. ;-)

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This is important to understand for CCD and Exmor where the sensors are called ISOless, because you will not get any result from increasing ISO in camera than you can get in the RAW conversion.  In these cases, ISO for the photographer becomes the same as the sensor scientist...meaningless...except for the jpeg he sees in the LCD on the back of the camera.
Valid and a necessary consideration for such devices. All my cameras don't work that way. ISO plays a role as I illustrated. Now why do such systems even have an ISO setting?
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« Reply #54 on: May 24, 2013, 07:22:54 PM »
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Now why do such systems even have an ISO setting?

Because you and I would yell and scream if it didn't.  :-)

Not to mention the chimpers of the world...which often includes me.
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« Reply #55 on: May 24, 2013, 07:39:29 PM »
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With today's high performance sensors such as the Sony Exmoor, ETTR is less important than it used to be and it is often more expeditious to use matrix metering and adjust the exposure if the camera histogram is too far to the left. However, bit of highlight headroom is sometimes advisable and one can make corrections with the raw converter. Remember that SNR varies with the square root of the exposure, so underexposing by one whole stop (not advisable in most situations) reduces the SNR by only a factor of sqrt(2).

Bill

Bill,

Why is ETTR (Optimizing/Maximizing Exposure) less important? 

Is it the greater dynamic range from the new sensors giving us greater "slop" range?  (I don't really mean that as slanted as it sounds.)

I understand that there are different conditions we shoot under...and there are time where it is more important to get the shot then it is to maximize the dynamic range.  But there are still times where we want (need) to maximize it.  How has that changed?
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« Reply #56 on: May 24, 2013, 07:40:32 PM »
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Now why do such systems even have an ISO setting?

1) To make the jpegs come out right.
2) So you can chimp in dim light.
3) tradition
4) for the amusement of the photographers.

Jim
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« Reply #57 on: May 24, 2013, 08:20:14 PM »
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For a photographer, the exposure net result includes the consideration of ISO.


This is a photography discussion board and despite the heavy dose of scientific discussion on this board, I think many of are photographers so those practical considerations are important.
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« Reply #58 on: May 24, 2013, 08:35:45 PM »
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This is a photography discussion board and despite the heavy dose of scientific discussion on this board, I think many of are photographers so those practical considerations are important.

Then I think you should include the rest of the quote...

This is important to understand for CCD and Exmor where the sensors are called ISOless, because you will not get any result from increasing ISO in camera than you can get in the RAW conversion.  In these cases, ISO for the photographer becomes the same as the sensor scientist...meaningless...except for the jpeg he sees in the LCD on the back of the camera.
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« Reply #59 on: May 24, 2013, 09:00:17 PM »
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1) To make the jpegs come out right.
2) So you can chimp in dim light.
3) tradition
4) for the amusement of the photographers.

IOW, for this audience who I assume captures raw data, nothing useful. OK, I do like a little amusement.
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