Ah, a few thoughts about ISO-less

Started Jul 10, 2013 | Discussions thread
Jeff
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Theory versus Practice ...
In reply to bobn2, Jul 11, 2013

The problem with this ISOless concept is that it just doesn't buy that much practical utility.  The core idea is to set aperture and shutter independently at the time of exposure, then adjust gain afterwards to map the exposure to a desired image. That can work only if your sensor has substantial usable dynamic range beyond that required in the image.

To put it another way, if I want to minimize noise by working near the saturation limit of the sensor, then shutter and aperture are not independently set. I might as well just work at base ISO. At the other extreme, the amount of noise I'm willing to tolerate  again couples shutter and aperture so I could just as well work at my maximum acceptable ISO.  It's only between these two limits that one gains independence in the choice of shutter and aperture. With current technology that's generally a range of 3-4 stops at most, and often less with small format cameras.

In practice I'm constantly concerned about controlling noise. When I can I maximize exposure. But sometimes I have to compromise, such as when shooting indoor sports under poor lighting. In those conditions I very definitely want to know the effective ISO at the time of exposure so that I can reach a tradeoff in motion capture, dof, and noise.  You can talk ISOless until the cows come home, but in practice I *want to know ISO at the time of exposure* in order to visualize the image I'm trying to create, noise and all.

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