ISO 100, OMD-EM1II and firmware 3.0?

Started 2 months ago | Questions thread
bobn2 Forum Pro • Posts: 61,716
Re: Basics of digital camera ISO

Architeuthis wrote:

Chris Noble wrote:

Native vs. extended. Extended is not just at the top and bottom: In Panasonic cameras, the 1 eV ISO steps are native (analog steps) and the 1/3 and 2/3 steps between them are extended (analog + digital).


What do you mean with "digital"? Postprocessing of the already digitized information (=digital multiplication of the digital number delivered by the A/D converter with 1,33 and 1,67)? Or does the digitalization range of the A/D converter change (e.g., when maximum intensity readout would be e.g. 5V: from 0V to 5V it would change to 0V to 5-2.5/3=4.17V (+1/3 EV) or 0V to 5-2.5*2/3=to 3.33V).

I think this statement illustrates well why Chris' definitions of 'native' and 'extended' isn't a very good one. He's about the only person I know of who would think of the 'in-between' ISO settings as 'extended', and in fact, it's a very odd usage of the word 'extended'. They don't 'extend' the ISO range, they fill it in.

His example is entirely spurious, because you don't know (or care) what are the internal voltages used within the camera - and actually his example is completely unrealistic, no camera would be using a voltage as high as 5V for 'full scale', it simply requires too much power to drive a signal to 5V at the speeds required (I know old fashioned logic used to work with a 5V signal, but that just has to be 'on' or 'off', so the precision of the control doesn't matter too much), generally the voltages used are around a volt or so. But really, for the photographer, it's irrelevant. People who have believed the 'ISO is gain' calumny tend to concentrate on voltages, because they think that's what it's about.

Maybe someone could open a separate tread on ISO and working principles of the MFT sensors and at the end we all know exactly how the sensor is working

ISO setting is independent of the sensor.

Ah now I see from where some of the problems arise: in this definition the sensor is just the photoactive surface, while for others the sensor is the entire arrangement up to the digital numbers delivered...

That's a common problem in this discussion, although also an irrelevance. When you realise what the photographic process is, and what ISO actually does, you realise that whilst where the sensor starts and stops is of academic interest, it's irrelevant to the discussion. ISO says what lightness should result from a given exposure. To determine the lightness in the output file, all the camera needs to be able to do is measure the exposure in each pixel. 'Gain' doesn't change the exposure in the pixel, but it can change how accurately it is measured. People have difficulty with this concept because they tend to call both the input and output 'exposure', in which case they think of 'gain' as giving a bigger 'exposure' from a smaller one, but that is not what is happening. Exposure and lightness are different things, which is why two words are needed.

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263, look deader.

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