Underexposing vs. Raising ISO: a question for the sensor experts

Started Jul 17, 2012 | Discussions thread
jfriend00
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Re: See above
In reply to Marianne Oelund, Jul 20, 2012

Marianne Oelund wrote:

mnodonnell wrote:

If you came across a scene, tripod in tow, and you measured it to have 10 stops of DR (I don't know how to do it, bet let's say it could be done), you wouldn't match the 10 stops with an ISO equal to 10 stops (1600), would you? If you're in a position where the exposure time is of no consequence isn't it always best to shoot at base ISO?

Yes, see my correction above. You do not want to use an ISO higher than where the camera DR matches the scene DR, but going lower, down to the slowest shutter speed you can tolerate, is better.

I wonder if this would be an interesting innovation for Nikon to build in a new auto ISO mode perhaps called auto-DR-ISO that you'd set a min shutter speed and the camera would use its metering sensor to detect the DR of the scene (perhaps ignoring small spectral highlights like point reflections) and apply all this logic for us that we're talking about. The hard thing for us in doing this is knowing how much DR we have in the scene without taking a bunch of test shots and examining the histogram.

We could set the aperture and min shutter speed as inputs and a this auto-DR-ISO mode would first get us the max light it could to the sensor with our min shutter speed and set aperture (as needed) and then raise the ISO as needed only until it ran out of DR. It could use this logic exclusively in the ISO-less area of the curve (higher ISOs), but perhaps favor an ISO raise (even at the expense of some DR) in the lower ISOs where there's some advantage to raising the ISO.

This would produce many shots that weren't as bright as needed and we would fix that in post, but retain more DR than if the camera raised the ISO as far as needed to get ideal brightness and give us the flexibility of raising the brightness in different ways than the camera would do it with an ISO raise (like we raise shadows, but not highlights - thus preserving/enhancing recorded DR).

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