ISO 100, OMD-EM1II and firmware 3.0?

Started 2 months ago | Questions thread
Chris Noble
Chris Noble Veteran Member • Posts: 3,144
Re: Basics of digital camera ISO

Architeuthis wrote:

Chris Noble wrote:

A lot of confusion in this conversation. Might be useful to start with the basics:

In a film camera, ISO refers to the sensitivity of the film. In a digital camera, the sensor sensitivity is fixed. The term ISO is used in a different way: the ISO setting controls an analog gain stage between the sensor output and the A/D converter. The higher the ISO setting, the higher the analog gain. The "base" setting is the lowest analog gain. The "native" settings are the various analog gain settings. The "extended" settings are extensions beyond the native settings that are obtained by digital scaling after the A/D converter. Because the extended-ISO scaling is digital, there is no benefit if you are shooting Raw as you can effect the same scaling in post-processing, with finer control.

Hi Chris,

You say that upon increasing ISO the analog gain, before digitalization is increased. From which source do you have this information?

You can observe it by shooting the same exposure at various ISO settings and looking at the Raw histogram.

It is in contrast to this description here, that has been made by an internationally recognized astrophysic scientist (these people need to understand very well the basics of sensors and optics):

http://www.clarkvision.com/articles/iso/

Roger Clark agrees with me. He says "ISO chooses a range to digitize", and it's always the bottom part of the range. The analog multiplication spreads that range across the entire range of the A/D. Can you point to any part of his description that says something different?

Or is it maybe a mixture of both analog amplification and digitalization at the A/D converter in case of the OMD cameras that makes th edifferent ISO?

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).

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.

And is it possible to provide trustworthy sources about the difference between extended and native ISO?

Look at the Raw histogram. Missing codes and A/D range limitations indicate digital gain steps.

Will Extended ISO100 or 64 prevent output clipping compared to base ISO 200?

No; the clipping just occurs in the middle of the A/D range.

Several people say, based on their own trials, extended ISO even promotes it, bobn2 claims the opposite (although he insists that the sensitivity of the sensor is an invariable constant, so output clipping should be the same at base and extended lower ISOs)...

Wolfgang

Examining the Raw histogram carefully for missing codes and range limitation answers that question, but each manufacturer uses a different combination of analog and digital gains.

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