Olympus OM-D (EM-5) comparison samples are now.. (continued)

Started Mar 17, 2012 | Discussions thread
Andrew Westlake Senior Member • Posts: 2,928

bobn2 wrote:

However, the fact seems to remain that you photograph the same scene with usually the same lighting ('critically-controlled level') at the same ISO settings and get very different exposures for different cameras. How does that happen?

The ISO testing uses critically-controlled lighting. Once you know the results of the that, nothing else needs to be shot under 'critically' controlled lighting (i.e. to a fraction of an EV) , it just needs to be shot to a controlled output brightness. Then, by the very definition of ISO, it doesn't matter whether the light level is slightly different and you compensate by changing the shutter speed - if the grey patches are rendered at the correct output brightness, you've got the same exposure.

Put simply, you can adjust the shutter speed to compensate any changes in the lighting, just as you do all the time when taking photographs. This means you can compensate for how the lights can drift slightly over time (for various reasons); alternatively you can allow, for example, other lights of the same type to be switched on in the studio at the same time, perhaps to shoot a resolution test chart. It simply doesn't matter if they shift the light level in the studio comparison setup by 1/3 stop. This in turn means we can make better use of studio time and get testing done more quickly.

To pre-empt the smart next question, yes we do know what the various tonality-tweaking controls are called, and we do turn them off first. This despite the fact that it's not even strictly necessary - Canon ALO doesn't do much unless it sees a face, and the various Apical-equipped brands (Nikon, Olympus, Sony) don't tend to respond to the limited DR of our test scenes. Panasonic iDynamic doesn't really seem to respond to anything .

So, just to reiterate - the studio comparison shots are not ISO tests - they've not necessarily run under strictly-controlled lighting, for entirely pragmatic reasons. We've also recently changed the entire lighting setup to one that's sensibly dimmable, which means we don't run out of shutter speeds when testing cameras that can run at ISO 102800, and therefore don't have to mess around with ND gels over the lights. This has changed the base light level - and it simply doesn't matter given how our testing regime works.

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Andy Westlake

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