I've tried to measure the focus speed of the GH3, compared with the GH2. I did so in two lightning conditions, moderate indoor light (6 EV), and very low indoor light (3 EV). I also used two lenses, the Sigma 30mm f/2.8 EX DN and the GH3 kit lens Lumix X 12-35mm f/2.8.
I tested them by setting the cameras on a tripod, with centre spot focus mode enabled. And I put a small figure on the table in front of the cameras, with a distance of about 40cm. When turning on the camera, the lenses are usually reset to around infinity focus.
I video recorded the process using a GH1 camera. To measure the time the camera needs to focus on the figure and take the picture, I've analysed the audio, to find the time from my finger taps the shutter button, until the camera snaps the picture.
Here are some example tests in moderate light (6 EV):
And the results are:
|Lens / Camera||GH3 (6 EV)||GH3 (3 EV)||GH2 (6 EV)||GH2 (3 EV)|
|Lumix X 12-35mm @ 35mm||0.23s||0.74s||0.43s||0.45s|
|Lumix X 12-35mm @ 12mm||0.18s||0.25s||0.27s||0.28s|
In the table, we can note that in the GH3 excels in good light with the Lumix X 12-35mm zoom lens, especially in the wide setting. This is as expected: The GH3 can use the higher framerate for the AF sensor output in bright light.
In dim light, though, the results are a bit unexpected: The GH2 comes out the best. This may be down to the fact that the GH2 is more mature, the firmware has been updated some times for better AF performance. I guess the GH3 will too, and probably the AF performance will be tweaked for the better in the future.
There is also the odd result that the GH2 and Sigma 30mm combination performs better in very low light than moderate light. I would attribute this to some random variations. After all, these are just single observations.
The GH3 performs very well in reasonable light, especially with the Lumix X 12-35mm f/2.8 kit zoom lens. However, in very dim light, it is not as good as the GH2. However, keep in mind that the GH2 has a more mature firmware.