Nex-7 vs EM5 Shutter Speed comparision at ISO 200

Started Apr 3, 2013 | Discussions thread
texinwien
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Re: Nex-7 vs EM5 Shutter Speed comparision at ISO 200
In reply to CosmoZooo, Apr 4, 2013

CosmoZooo wrote:

No shooting, but some friendly advice that you have a lot to learn here, and it's a pretty complicated topic. Try to take your time, keep an open mind and not jump to conclusions while you're still figuring things out.

You're right and actually I kind of found the answer I was looking for although not entirely.

When Mjankor said:

"Dxo and sensorgen ratings are not actually related to manufacturers iso ratings. Both cameras are correct, or within a third of a stop or so, as per the standard."

He didn't give me much explanation but I found one here:

http://www.dpreview.com/forums/post/50892647

What that post as well as some other info I quickly read explained is that Measured ISO as stated by dxomark or sensorgen are somehow related to dynamic range and clipped highlights and not to ISO as would be measured by a light meter.

In the case of a light meter the ISO on the OMD is indeed with 1/3EV so I get at least that part now. All this talk about OMD overstating ISO is wrong and by people who themselves don't understand what Measured ISO actually means and then confuse folks like me who are new to all of it and are just trying to understand all the data flying around.

So essentially one can and should expect similar shutter for the same f.stop and ISO. If it is a bit off, it's only because different cameras may under or over expose a bit.

What I still don't quiet get is what is the Measured ISO really saying when comparing these cameras. Is that suppose to give me some sort of idea of a dynamic range vs noise trade off...I am still confused so if anyone can clearly explain please do.

It took me while to sort this ISO nonsense out but I am glad I found some info finally that was helpful.

The short story:

  1. The optimum exposure for every RAW photograph is the one that puts the most light on the camera sensor, taking into account the artistic and technical limitations on aperture and shutter speed, while avoiding 'blowing out' important highlights - call it saturation sensitivity-based exposure
  2. The optimum exposure for a JPEG photograph is the one that results in the desired brightness of the JPEG image that's produced by the camera. Call this ISO setting-based exposure
  3. Most camera makers choose ISO settings that are higher than the saturation sensitivities, e.g. ISO setting 200 = saturation sensitivity 159 on a NEX 6. The reason they do this is that they're making a tradeoff or compromise, accepting a little more noise for a lower chance of blowing out the highlights.
  4. As long as a camera meters within the allowed variance at different ISOs, it's not correct to talk about 'cheating'.

The NEX-6 leans more toward lower noise and lower highlight headroom at any ISO setting than the E-M5 does.

The next thing to consider is Exposing To The Right (ETTR), wherein a RAW photographer (mostly) ignores the ISO setting labels and sets exposure based on the camera's saturation sensitivities, instead.

There's a lot to learn about. Some people find it fascinating, some find it a distraction. I think it's pretty interesting...

Here are a few links on saturation sensitivity (aka DxO Measured ISO) vs. ISO settings (as labeled on the cameras):

  1. Wikipedia: Film Speed | Digital camera ISO speed and exposure index
  2. DxOMark: Pushed Sensitivity - Let's Make It Clear
  3. DxOMark: Measurements - ISO Sensitivity
  4. DPReview: Sense and Sensitivity
  5. Imatest: ISO Sensitivity and Exposure Index

I've been collecting these links as I come across them - the subject is somewhat complex, and it often trips even very intelligent people up.

Have fun!

tex

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