S5 base/native ISO

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pdk42
pdk42 Senior Member • Posts: 1,107
S5 base/native ISO

I'm a bit confused by things I've read on the sensor of the S5. I've always understood that sensors have a "base ISO". Now I know that ISO is a complex (and to some degree arbitrary) concept in digital cameras, but let's just say that by base ISO, we mean that we'll get an image of acceptable brightness with almost but not quite full sensor wells when we expose using an ISO-calibrated meter at that setting. In other words, there's no/minimal amplification of either the analogue signal before D to A or digital amplification after if we use "base ISO".

My understanding was that on this measure the base ISO of the S5 is 100. However, there are lots of articles on the web quoting the "dual native" capabilities of the S5's sensor and these invariably put the native ISOs at 640 and 4000.

Can anyone clarify what's going on? Is the base ISO really 640 and ISO 100 a 2-and-a-bit stop ETTR? That might explain why there's so little room for highlight recovery - it's even worse than the Olympus EM1.3 - which is quite counter-intuitive given the difference in size of the charge wells.

Ideas?

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