ISO 100, OMD-EM1II and firmware 3.0?

Started 2 months ago | Questions thread
bobn2 Forum Pro • Posts: 61,766
Re: Meaning of base vs. extended ISO

Architeuthis wrote:

The situation is confusing, but I did now some recherches in Internet and think I know now what extended ISO means:

Be careful of 'researches on the internet'. A whole load of the articles on the internet are written by people who think they know about a topic, but don't. 'ISO' is one of the worst. In the early days of digital photography, a whole load of web sites wrote tutorials on 'ISO' and got it entirely wrong.

Here, among other decriptions, is an interesting post about the difference between native (and base) ISO and extended ISO:

That article is very wrong. The author hasn't done his research, hasn't read the ISO standards, doesn't understand how camera electronics work. In short, it's garbage. Don't take anything from that at all.

Chris Noble was very close to it.

He was close to something completely wrong, hence wrong himself. The terms 'native' and 'extended' ISO are essentially meaningless. Camera manufacturers will give some ISO settings numbers, which in effect means that they say that those settings adhere to the ISO standard, and that is all. The other ones are simply ones for which they are not prepared to say that. In the case of low ISO settings, it is likely because they don't have sufficient headroom to cover the fill exposure range required for that ISO (but not always), for high ones, likely because the noise is enough that they want to say at users's risk only. There is no hard and fast technical diagnostic which allows one to say whether on any particular camera an ISO setting should be 'native' or 'extended', only the manufacturer's claims.

The question is just, whether the raw file is affected by the extended ISO setting or only the JPEG is. In other posts/articles, not referenced here, I saw that indeed the raw file can be affected by extended settings, but not always.

As I said, the ISO standard does not apply to raw. The camera manufacturers' ISO control will affect the raw file, but how it does is completely unstandardised, and to know how it does you have to do your own research, using tools such as Raw Digger.

The way depends on the camera model and manufacturer. In the case of EM1-II people are saying that the digital information is processed towards highlight clipping, improving S/N in less bright pixels (dynamic range at the cost of S/N). So extended ISO remains useful for people that work with JPEGs out of the camera, but not the ones who postprocess raw files...

That's an entirely wrong conclusion. John got it right, the additional exposure will always bring benefits by increasing the shot noise SNR, irrespective of whether you shoot JPEG or raw.

For my needs I must conclude the extended ISO 64 and 100 are useless. It would need lower ISO in circumstances where I would require lower sensor sensitivity, not leading to output clipping (e.g. having sunbursts directly in the frame)

ISO has nothing to do with sensor sensitivity. That's another wrong idea put around by the merchants of ISO misinformation.

Hopefully future MFT sensors will provide lower base ISO (but I am quite happy with my EM1-II as it is)...

You're completely wrong on what ISO is, what base ISO is and what is the effect of lowering base ISO.

There is also no way that I doubt DxO benchmarks. The only way to challenge them would be to make benchmark by my own and I do not have the means, time and also not the moods to do so (prefer to go diving and make photos)...

I'm not sure which DxOmark measurements you're talking about. Whilst they make some errors, overall they are quite good. It's just understanding what the actually signify. Their 'measured ISO' measurement is actually very useful indeed, it's just misnamed. It isn't 'measured ISO'. A better name would be 'saturation exposure', where the measurement of exposure is a non-standard ISO rating.

Here the interesting description how DxO measures ISO sensitivity (and it is clear from the description and what is said above that extended ISO64 (and ISO100) and base ISO200 in the EM1II are almost the same regarding raw files):

Thank you. I'm very familiar with how DxOmark (not DxO) measures it's 'measured ISO' and why it doesn't conform to the ISO standard, and what it does actually measure. What is not the same, as both John and I tried to explain to you, is that if you set 100 ISO and use you meter as intended, you will get twice the exposure, than you would using 200 ISO. which will give you less noise., by a factor of 1.4.


Thanks for your kind attempt to educate me on a topic which I know a whole load more about than the authors of the sources that you have used. You went to bad information sources and came back with very wrong information.

I suggest a better source than the one you have used is the one written on this site by Richard Butler, the Technical Editor here.

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263, look deader.

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