Back by popular demand: Nex-7 vs OMD

A larger sensor collects more light at the same exposure settings (same exposure density times greater area yields greater total exposure to light).  This results in a higher* signal to noise ratio allowing you to shoot at a higher ISO.

*Assuming similar sensor technologies.  An older FF might be outperformed by a state of the art APS-C, and the sensor in the RX100 might outperform the first micro 4/3 sensors (or at least be closer than it should, based on size).

As for the Oly ISO settings, that might result in Oly files looking better than they should in comparisons that use the same ISO.  So the trick is to compare using the same exposure settings.

DXOMark shows SNR at measured exposure settings rather than nominal.  It shows the EM5 tracking very close to the NEX-7 through measured ISO values or around 2600 or so (where NEX-7 is set to 3200 and a little before EM5 is set to 6400) with the EM5 lagging by a small bit (1/4 stop or 1/3 stop - nothing significant) and then widening to a little under a stop.

Given that there's a 1.33X crop factor between them, you'd expect APS-C to enjoy almost a 1-stop advantage, so the fact that the EM5 is so close represents an impressive sensor by Sony. (Hopefully a sign of improvements yet to come to APS-C).

So based on samples I've seen, EM5 results are impressive.  But seeing the dxomark test, I have to interpret those results with a grain of salt as they high ISO settings aren't as high as on cameras I'm used to.  Still, knowing it's just behind the NEX models and a bit better than my A700, I'd be content using it (if I had other reasons for choosing it).

If I were picking a mirrorless camera specifically for low light, I'd probably go for a Fuji, but between the Oly and NEX, I'd probably choose a NEX-6 over the NEX-7 (because despite my generally high confidence in dxomark, I don't think the NEX-7 matches the 5n/6 from ISO 3200, even downsampled) but would have to seriously think about it - maybe test them out for low light focusing, and consider the lenses, where Oly offers the 17/1.8 (or Panny 20/1.7), 45/1.8 and 75/1.8 while Sony only offers the 35/1.8 and 50/1.8 with stabilization, and neither of those FLs appeal to me nearly as much as the Oly options.

- Dennis

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