Should you use ETTR at higher ISO, or only at base ISO?
Asked 10/31/2014
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2 answers
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I’ve often read that expose to the right (ETTR) is only worthwhile at a camera’s base ISO, because increasing ISO amplifies the signal in-camera and may reduce or cancel ETTR’s benefit. But in practice, I’ve found that on some cameras, images exposed as far right as possible can still look very clean even at ISO 1600 after normal RAW adjustment.
Assuming shutter speed and aperture are already constrained by motion blur or depth of field, does it still make sense to ETTR at higher ISO? Or is it better to stay at base ISO and give up on ETTR in those situations?
Please assume the goal is always to capture as much actual light as possible where feasible. I’m specifically asking about cases where exposure time and aperture can’t be changed further, so the only remaining variable is ISO.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
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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.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
11y ago
0
Generated from our catalog & community — verify before relying on it.
Yes—sometimes, but it depends heavily on the sensor.
If aperture and shutter speed are fixed, raising ISO does not add light; it amplifies the captured signal before readout. On cameras with relatively high read noise, that can improve the signal-to-noise ratio in the shadows, so using higher ISO to push the histogram right can be beneficial.
On sensors with very low read noise (often described as more ISO-invariant), raising ISO in RAW shooting gives little advantage beyond preview brightness and metering convenience, while increasing the risk of clipping highlights. In those cameras, ETTR by changing ISO alone may not buy you much.
What always helps is more actual light—longer exposure or wider aperture—so ETTR is most valuable when it comes from gathering more photons, not just from amplification.
In practice: if shutter and aperture are locked, using higher ISO to move the histogram right can help on some cameras, but not all. The best answer is camera-specific testing of your RAW files.
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