Exposure basics, lesson two point one (& ISO)

Started Mar 19, 2013 | Discussions thread
Timur Born
Senior MemberPosts: 3,879
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Re: It's about fair comparisons - not which is better
In reply to Anders W, Mar 20, 2013
However, is the majority really much different in this regard? If, for the moment, we bypass the more complex forms of metering, the meters of different cameras give pretty much the same reading at the same camera ISO in my experience. The manufacturers tend to follow the SOS ISO norm in this regard, just as they do with regard to the brightness of the OOC jpegs for an 18-percent gray target, wouldn't you say?

Curiously I just asked myself if Matrix/Multi-metering really has to follow any ISO norm at all?! And even if they follow the norms, we know that this only applies to JPGs and leaves room for applying digital instead of analog gain. The reason I came to that question is my observation of Fujifilm X20 images. There are ongoing discussions on how its JPG engine seriously smears away dark mids detail. When I saw the images I was instantly reminded of what the E-M5's "Auto Gradation" (AG) images look like when well lit areas border badly lit areas, which in turn makes AG lift the shadows heavily. This led me to believe that the X20 underexposes its images to apply digital gain afterwards.

To evaluate my theory I asked an owner to take some shots in RAW + JPG at different exposure compensation settings. Interestingly even at +2 (two!) EV exposure compensation there was nearly no highlight information lost and you have to do serious pixel-peeping to even find that. The images were shot at base ISO (100) and the only variable changing with EC was exposure time. My gallery holds examples of this in the X20 album.

So Fujifilm seems to haven chosen the same approach of leaving high headroom for whatever purpose. Bob's possible explanation of leaving room for exposure and processing decisions with matrix metering seems to make some sense. I can think of another one: "Trying to keep the customer from harming himself", aka people tend to misjudge and blow highlights. But as a result of that decision on the small 2/3" sensor shadows and more importantly mids reveal too much noise that is then all plastered with heavy-handed noise reduction in JPGs. Also seems like many image example are too dark, which again puts the whole "ISO norm" thing in question.

Hopefully this isn't becoming too much of a tendency, especially if the motivation really is to mother customers instead of some sensible technical reasons.

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