So... I finally come to a decision to go with the OM-D... Is there any big hand users out there?

Started Mar 13, 2013 | Questions thread
texinwien
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Further Reading on ISO for Those So Inclined
In reply to texinwien, Mar 14, 2013

Not only has DPReview contradicted the misconception that the E-M5 received a 'performance bonus' in its high ISO tests due to ISO 'tricks' or 'cheating', DxOMark and others have addressed the question of cheating and tricks as it relates to differences between manufacturers' published Exposure Indices (EIs aka 'ISO Settings') and ISO Sensitivity measures (of which DxoMark's 'measured ISO' is one).

Here a few links with excerpts from those links - direct quotes are shown in italics, my comments are included in square brackets and any emphasis added is mine:

DxOMark - Measurements - ISO Sensitivity

As tests show, the ISO settings [aka Exposure Indices or EIs] reported by camera manufacturers can differ significantly from measured ISO [a type of Saturation-based Sensitivity measure] in RAW. This difference stems from design choices, in particular the choice to keep some “headroom” to avoid saturation in the higher exposures to make it possible to recover from blown highlights.

DxOMark: RAW ISO measures are inferior to manufacturer ISOs: is this a problem?

The RAW ISO measured value [a type of Saturation-based Sensitivity measure] is almost always inferior to [lower than]* the ISO [aka Exposure Index or EI] that you decided to use with your camera. Take a Canon EOS 60D, for instance. When you select ISO 200, the measured RAW ISO sensitivity is 160. At ISO 800, the measured value is 632.

* Regarding DxOMark's use of the phrase 'inferior to' here - DxOMark is a French company, and I believe the use of 'inferior to' in this sentence is due to a false translation - what some translators call a 'false friend'. 'Inferior to' implies a value judgement, but I believe the actual English phrase the DxOMark writers were looking for was the value-neutral 'lower than'. In other words, they were simply trying to say that the Saturation-based Sensitivity is almost always lower than whatever ISO Setting one might choose. Note also that this passage is not specific to the E-M5 or to Olympus cameras. It is a generalized statement applying to the world of digital cameras with no brand or model specificity implied.

...

In fact, it is precisely the JPEG ISO value [aka Exposure Index or EI] that all the manufacturers publish. They do so because JPEG (or any RGB) output is the visible output that photographers use. So when you select ISO 800 on your camera, you’ll have a JPEG ISO at 800, but the RAW ISO will be at (for instance) 550. The JPEG results are achieved by playing with the tone curve shape. This is absolutely legitimate: the ISO standard allows manufacturers to use this JPEG value. They are not cheating.

Not cheating—okay. A trick? Maybe. The RAW-to-JPEG conversion allows cameras to achieve improved speeds, and to boost ISO values. And this is nothing new. What happens today with digital cameras also happened in the past with film cameras. When manufacturers produced an 800 ISO film, for example, they often used revamped 400 ISO film, and simply “asked” that it be processed differently. So when lab operators received a film labelled 800 ISO, they treated it differently (keeping it twice as long in the chemicals, for instance) in order to produce a stronger signal on the film. Digital camera manufacturers have simply implemented this same strategy in the camera body, and so could be seen as a “good old tradition.”

Moreover, underexposing the RAW file allows manufacturers to use their own complex algorithms to obtain a better output for the highlights while retaining good medium tones.

Note: I take issue with DxOMark's characterization of this practice as 'maybe' being a trick, since 'trick' implies something dishonest or deceptive. What manufacturers are doing here is accepted practice, and it is practiced by multiple manufacturers. It comes from a long and well-known tradition stretching back to the days of film. If it's a trick, it's one that everyone knows is being played - some trick, huh?

Imatest: ISO Sensitivity and Exposure Index

Exposure Index [aka EI or ISO Setting] and [ISO] Sensitivity are closely related and sometimes used interchangeably, but should be kept distinct. For example, one might say, “The camera’s Saturation-based ISO sensitivity is 80 when the Exposure Index [aka EI or ISO Setting] is set to 100.


One thing I have to point out here - the ISO standard was pieced together over several years based on proposals and papers written by digital imaging experts. One thing I often see when I point out the specifics of the standard is people taking issue with how the standard is written. When they recognize that the standard doesn't say what they thought it did, they complain that the standard is 'wrong' or 'too permissive', but I'd argue that this is a facile way of looking at things. The experts who wrote the standard knew full well exactly what they were writing - better, almost certainly, than you or I or random Internet forum poster 'Mr. X'.

Let that sink in. Those who wrote the papers at the foundation of this ISO standard,a nd those who went on to compile them into the current standard did so with the express intention that the standard do exactly what it does today. They specifically DID NOT write it to do what you think it should do. They also specifically DID NOTwrite any other standard that does what you think should be done, and I'm quite certain they did that consciously and with good reasons that you may simply not yet have grasped

I have to admit, it's a bit of a complex subject to digest, but I think it's worth it if you're interested, and mandatory if you want to argue or discuss with others aboutit.

I will also be the first to admit that I'm still learning about it. I've come a long way in the past 10 months or so, but I still have a long way to go. Fascinating stuff!

tex

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