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I have read in a number of places that exposing to the right (ETTR) only makes sense at your camera's base ISO, with the justification being that if you are boosting the gain in camera (by raising the ISO), you are negating the benefits of ETTR.

My own experience is very different. I have found that if you ETTR maximally, even at ISO 1600 (on a 5D Mk3), the noise is fairly negligible once the photo has been adjusted correctly.

Obviously the huge benefit to raising the ISO is it gives you much more room to manoeuvre, allowing you to maximally ETTR in situations where it would be impossible at base ISO.

So does it make sense to expose to the right at high(er) ISOs, or to select high(er) ISOs specifically so that you can ETTR?

Note: For anyone else answering, please take it as a given that the ideal is to get as much actual light into the camera as possible. I am interested in situations (in my experience, most situations) where something has to give - you need a fast shutter-speed to prevent motion blur, you need to close up the aperture for more DoF – in these situations where you can't just let more light in, what is the best strategy? To forego ETTR or boost the ISO to achieve ETTR?

  • I think that photo.stackexchange.com/a/6622/1943 covers this pretty well. – mattdm Oct 31 '14 at 14:24
  • possible duplicate of Is high ISO useful for photography? – mattdm Oct 31 '14 at 14:25
  • That second question is very general but I think the top answer covers this, even though it doesn't really address ETTR explicitly. – mattdm Oct 31 '14 at 14:26
  • FWIW I think this is a different question. I'm not asking about whether or not I should use high ISOs. I'm asking about the tradeoff between ETTR and using high ISOs which is not the same thing. In an ideal situation with plenty of light, of course the base ISO should be used, but I'm interested in un-optimal situations where the choice is either 'correct' exposure at base ISO or maximal ETTR with a higher ISO. – Undistraction Oct 31 '14 at 15:21
  • @Pedr It probably depends of how much noise your specific hardware introduces when increasing ISO, and it might even vary at different ISO intervals. My advice would be, when possible, try doing both, then compare the results in post. – Jim Bolla Nov 4 '14 at 19:07
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It depends on the properties of the sensor in your camera.

Raising the ISO setting means you amplify the signal before reading it out, this means your signal level is higher and thus read noise is lower relative to the signal, improving the overall signal to noise ratio.

However Sony Exmor sensors (found in all NEX bodies, and many current Nikon/Pentax models but not Canon) and some newer Panasonic sensors have such low read noise that it doesn't really matter if you boost the signal before readout or not.

With such sensors there is little benefit to using the ISO setting at all when shooting RAW in manual mode as all you are doing is increasing the chance of overexposing the image somewhere.

  • Thanks. I tagged the question as 5D MK III and this is the sensor I'm specifically interested in. So in low light, is it better to forego ETTR or achieve maximal ETTR by boosting the ISO? – Undistraction Oct 31 '14 at 15:23
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    @Pedr With a 5D mkIII the best performance is achieved by getting as much light in as you can (by opening the aperture/using a slower shutter), and then pushing up the ISO as high as you can (without overexposing any important areas of the image). – Matt Grum Oct 31 '14 at 16:12
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I also think that it depends on the camera. Factors include the bit-depth of the A/D, the various sources of noise, and unknown details.

With all the theory requiring possibly unknown parameters even if the model is right, the only thing to do is a real test.

Assuming the histgram fits completely in the exposure so you aren't deciding which end to cut off, shifting the darks up is expected to give less quantization as there are more numbers for the zone. But, if the number of discrete electons being measured is also in the same range, multiplying it won't reveal any more shades other than noise.

Note that adding more light (e.g. longer exposure) without cutting off whites is always a clear win. Cranking the ISO is what I'm lamenting on above. Assuming you don't grt blooming or crosstalk in the brightest... so try it.

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    +1 The "more numbers in the zone" aspect of ETTR is often explained in a way that is somewhat misleading. There are more numbers because there are more photons to count when there is more light, not because of a quirk of digitization. More light is always good (at least, in the right places and of the right quality). – mattdm Nov 1 '14 at 13:22

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