I have been thinking about the Zone System and its goal of maximising image quality given the limitations of film sensitivity and the necessity to choose specific developing parameters.
Clearly you can't extract information that was never recorded or was burnt out but given that raw images can be tweaked in post processing, how critical is it get things exactly right at the outset? Does for example +/- 1 stop exposure compensation have any value beyond the quality of a jpeg (if you shoot raw+jpeg)?
Perhaps what I am asking is how much latitude do I have with post processing raw images? (Nikon D90 and P7100). I have zero experience with raw so far (in case you hadn't guessed).
Answer
It's very important, but depending on the dynamic range of the scene you're shooting. If you have bright skies, but also deep shadow areas, then the dynamic range may exceed what your sensor can capture. You will lose detail in the shadow or in the highlights, or both, even shooting in RAW. Shooting RAW means you retain more of the original information, but it doesn't extend the dynamic range of the camera.
If the scene is lower contrast you may have leeway to under- or overexpose by a stop and still not blow highlights or lose shadow details.
You can get an approximation of this by looking at the histogram (although it is derived from a JPG version of your image, so isn't 100% reliable).
There is more information and a higher signal to noise ratio in the higher exposure values than there are in the shadows. So if you do have leeway to adjust exposure, you're generally better off to "expose to the right" (moving the histogram to the right hand side) and then you can adjust the exposure down in post processing if you want to. If you have most of the histogram to the left, and try to raise the exposure in post processing, you're more likely to end up with noise or banding.
More about expose to the right here and here
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