Exposure basics, lesson two point one (& ISO)

Started Mar 19, 2013 | Discussions thread
bobn2
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Re: Pushing ISO in order to ETTR
In reply to richarddd, Mar 21, 2013

Not quite. Increasing ISO so as to ETTR while keeping exposure constant is an advantage in that region where the relationship between camera ISO and DR is nonlinear, i.e., the region in which read noise (as measured in electrons) keeps falling with increasing camera ISO. On the E-M5 it falls up to about ISO 1600 although the main read-noise reduction occurs between ISO 200 and ISO 400.

I thought the EM5 had relatively constant read noise from ISO 800 on up:

http://www.sensorgen.info/OlympusOM-D_E-M5.html

By the way, probably better to refer to "ETTR via higher ISO" as "BTTR" (brightness to the right) or "GTTR" (gain to the right), as the exposure is unaffected.

Those who insist that people use the official definition of exposure might look a bit odd using their own versions of the well accepted ETTR

I wouldn't call ETTR 'well accepted'. Talking to its proponents, you find most have their own individual definition. In fact the original motivation for ETTR (giving more raw levels) was completely bogus. The effect of ETTR is due to increasing exposure at base ISO or minimising read noise at higher ISO's. The idea that it was down to anything else is probably due to not seeing the obvious for lack of knowledge about what the effects of raising exposure are. In any case, ETTR throws the Petersen 'exposure triangle' out of the window, so its not a strong starting point ofr proponents of that.

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Bob

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