Exposure basics, lesson two point one (& ISO)

Started Mar 19, 2013 | Discussions thread
Anders W
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Re: It's about fair comparisons - not which is better
In reply to Jack Hogan, Mar 20, 2013

AndersW wrote: Let's assume, as in the above example, that the G3 and the E-M5 are shot at the same exposure (same light, same lens, same f-stop, same shutter speed). Then consider the following questions and answers.

Question: If the cameras are set to the same camera ISO, say 1600, will the G3 clip the highlights at a lower light level than the E-M5?

Answer: Yes. It follows directly from the DxO "measured ISOs" of 1481 and 782, respectively, that the G3 will start clipping about one EV before the E-M5 does.

OK, but in fact the G3 was the one properly set up for the assignement. So the EM5 recorded 1 additional stop of highlights that were not called for at the expense of 1 stop of shadows that instead were called for (ok 2/3 of a stop to be precise). You are fired

No. If you had read and understood the rest of my reply you would have realized that if, in the scenario you outlined, you keep the E-M5 at ISO 1600 rather than raise it to ISO 3200, the E-M5 gains one additional EV worth of highlight headroom without sacrificing anything in terms of shadow noise.

If you think differently, then please answer the following question: If exposure is kept constant, as it is in the scenario you outlined, the amount of light hitting the sensor is exactly the same regardless of whether the camera is set to ISO 1600 or ISO 3200. So on what grounds would shadow noise be worse in the first case than in the second?

And so with the other questions. AndersW, if you've followed my posts you know that they are only about two issues: that manufacturers label in-camera ISOs inconsistently and that therefore it is often misleading to compare two cameras' performance at the same in-camera ISO aotbe. I did not bring up the EM5-G3 example, ultimitsu did in a thread titled 'DxOMark's measured ISOs vs. manufacturer ISOs', four threads ago. I merely chimed in with my opinion and for some reason texinwein and mjancor have been chasing me ever since.

I don't care about the EM5 vs the G3 (I am a DSLR guy), what I care about is fair comparisons.

I realize that. But my point is that you have in some important ways misunderstood what you refer to as an inconsistency in ISO labeling and therefore also misunderstood in some important ways what it takes to make a comparison fair. My response addressed one of these misunderstandings.

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