Are there any "rules" for using ISO?

Started Apr 3, 2013 | Discussions thread
GreenMountainGirl
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Re: Are there any "rules" for using ISO?
In reply to Barrie Davis, Apr 5, 2013

Barrie Davis wrote:

Spot metering only works if the subject represents a good target for metering. Just BEING the "subject" doesn't do that....

.... (statistically the chances of a subject by itself integrating tonally to the ideal target of an 18% grey are rather worse than a whole scene doing it with an averaging type reading.

The suggestion of spot metering has been put forth by OP, but although it sounds like a good possibility, I wondered about how it was more appropriate than evaluative metering.  Especially since it is often difficult to get that center spot to stay on a moving subject.

Evaluative metering endeavours to identify the nature of the subject being photographed. It does this by taking dozens of separated different area readings, instead of just one. Then, while also taking into account the general brightness level across those areas, it calls up an actual shutter speed and aperture from its database of known correct exposures for hundreds (thousands?) of subject types.

Although more sophisticated, isn't this also where we run into problems with trying to reach that "average" exposure?

Susan

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