Exposure basics, lesson two point one (& ISO)

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

Jack Hogan WQrote: 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

AndersW wrote: 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?

I see your point, bad example then.  The point is not favoring one or the other in a comparison in order to have useful apples-to-apples data.

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.

This was the example that brought this discussion to this point, on the effect that inconsistent ISO labelling across cameras and manufacturers can have on a naive evaluation of the SNR performance of two cameras :

Noise performance when both cameras are set to the same in-camera ISO = 3200

Noise performance when both camera's ISO dials are set so that they will produce the same mean raw value for the same signal*

My original opinion , which I continue to hold, is that it appears to me that the more useful of the two is the bottom one, but that most people would not know it.  In fact my sole mentioning it four threads ago has resulted in flaming that is still ongoing.

Cheers,
Jack

*From DPR's comparometer and trusting DxO, which I generally do.  In fact the EM5 is penalized by 1/3 of a stop less light, but you get my point.

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