Anybody here using base-ISO exclusively or predominantly?

Started 9 months ago | Discussions thread
Jeff Charles
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Re: Anybody here using base-ISO exclusively or predominantly?
In reply to nixda, 9 months ago

nixda wrote:

I am asking, because ETTR is a popular approach, but it's useful at base-ISO only.

The idea behind ETTR is to put as much light on the sensor as possible, short of blowing essential highlights. The technique uses the histogram as a gauge: When it is pinned to the right side, we've achieved "maximum" ETTR.

It's said that ETTR is "useful at base-ISO only", because, although increasing ISO will move the histogram to the right, it does not increase the actual exposure of the sensor. Only changes to aperture and shutter speed can increase actual exposure.

In real life, "maximum" ETTR is rarely possible, because the shutter speeds and apertures we choose are constrained by our need to control motion blur and to get sufficient DOF. However, maximizing the amount of light reaching the sensor should still be the goal. That can be achieved by using the widest aperture and the slowest shutter speed that the situation permits.

In fact, auto ISO can serve as a useful aid in achieving this objective, because it indicates the actual exposure that will result at the shutter speed and aperture we've set. For example, if we set shutter speed to 1/250 and aperture to f/5.6, and auto ISO goes to ISO 6400, it means that the sensor will receive very little exposure at those settings. We can then consider if 1/125 and f/4 would be "good enough." If we decide that they are, that gets us ISO 1600, and much better IQ.

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Jeff
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