Dynamic range refers to the camera's ability to provide decent detail in both the brightest and the darkest areas of a picture. After all, when you take a picture, the camera provides only one exposure and it is usually an average based on light tones, mid tones and dark tones. Mid tones might be exposed perfectly but light tones might be overexposed and dark tones underexposed. The less the dynamic range, the more likely this will be the case. And of course it is especially noticeable in images where there are both lots of bright areas and lots of dark areas.
Today, I compared the GH2 and E-M5 with a couple of pictures that had both bright areas (white clouds) and dark areas (shadows in the trees). As it turns out, neither camera was stressed by these conditions and both did a very nice job providing details in the clouds and sky while at the same time not being too dark in the shadows. Of course, the human eye would be able to see more deeply into the shadows than this, but a camera's sensor does not have the dynamic range of the human eye.
As far as I can tell, if there is a difference, it doesn't make a difference. These both look good to me, and quite similar.
However, I will try to find a more rigorous test. This will require a scene with even more contrast, with brighter brights and darker darks.
These two images are jpegs created from raw files in Lightroom 4. The lens was the Olympus 14-54II. Both were shot and 1/125th and F11. I used P-mode and autoISO. Both cameras set ISO at base levels of 160 (Pany) and 200 (Oly). In Lightroom I set WB at 5500 Kelvin. I used "Auto Tone" to equalize the exposure, contrast, and saturation settings. I used Lightroom's default sharpening settings.
If you want to see bigger files, they're here:
|Panasonic GH2 with Olympus 14-54II. A bit more magenta than Olympus even|
at the same WB setting. Note the "purple-ish" color cast in
the driveway asphalt. But the dynamic range seems the same as the Olympus
|Olympus E-M5 with 14-54II. Dynamic range seems to be equal to the Panasonic. To me, both look good.|
The next step with these images it to see if one file is easier than the other to bring up (i.e. lighten) the shadows, as the shadows here are darker than what my eyes saw. In other words, perhaps we can "engineer" more dynamic range better from one than the other.