New answers tagged noise
A digital sensor only has ONE sensitivity, its one native sensitivity, probably rated ISO 100 for most DSLR today. All a sensor can do is to collect the light photons hitting its cells. It cannot attract more photons. :) Then basically, all any higher ISO setting can do is to multiply the existing data values, shifting the data up in the histogram, which ...
The answer is not that simple, also because of the compression scheme SONY are using. Technically, between ISO 50 and ISO 100 all that is supposed to happen is exposure meter shift, 1 stop. That is, ISO 50 shot is supposed to be ISO 100 shot overexposed by 1 stop, just as Mr. Grum wrote. However if one starts to split hairs and perform noise measurements, ...
They have lower level of noise, but also a lower ceiling for highlights. ISO 50 is effectively doing ETTR and then scaling back a stop. Whether or not the ceiling for highlights has been reduced too much is up to the scene and what you're trying to do.
ISOs lower than 100 on the A7 are not "real" in the sense that they don't lower the gain on the sensor, they just instruct the camera to increase exposure time as if the sensitivity was lower. The net result of this is reduced highlight headroom. If you shoot RAW there is nothing really to be gained from any ISO setting less than 100.
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