ISO - does it matter if shooting RAW?

[Fabrice C.]

[font color=\'#000000\']No, ISO setting directly affects Raw files : the raw file is the data recorded by the sensor and the ISO setting tells the sensor which sensitivity to use. A same given amount of light might give, depending on the ISO setting an output level in your raw file of 0%, 50% or 100% of the output range.[/font]

[mcanyes]

[font color=\'#000000\']In practical terms you can correct a little more than 1 stop under or over. However, the correction is not linear and you run into distortion problems like odd colors or loss of shadow detail. To find out how much you can correct shoot a correct exposure and several over and under. Correct the over and under shots to look like the correct one by changing the exposure in software - don't use levels or curves. Then compare them and see how far you can go.
Michael[/font]

[Wayne Fox]

[font color=\'#000000\']If the sensor captures "raw" data while the shutter is open, is there really any difference if you change the ISO?  Seems like the only difference is the metadata stored with the image, but the actual data would be the same.  

So rather than changing the ISO, you could just underexpose some frames and get the same RAW data...as though you changed the ISO to get the exposure right[/font]

[font color=\'#000000\']All chips have a base level ISO. When you increase the setting you are asking the camera's electronics to boost the signal. This is much different than playing with the final output in the raw converter or Photoshop.

Michael[/font]