Of course, by this time, I have no first hand experience of the camera what so ever. My knowledge of the camera is solely based on images, video and text online.
In terms of technical specifications, not so much has changed. We have a higher video FPS rating at 1080p, as expected. And we have a higher video bitrate. Under the hood, there is of course a lot of technical details, for example a higher frame rate used for the contrast detection auto focus system (CDAF), which has the potential for better and faster autofocus. And there is a higher sensitivity, as well as the usual promise of a better dynamic range.
The really big change is the ergonomics. The GH3 is bigger than the GH2:
|Dimensions (w, h, d)||124 x 90 x 76 mm||133 x 93 x 82 mm|
The size accommodates a better grip, more space for buttons, three control wheels (the GH2 had one single only), more connectors. As the camera does not really take up that much more space in the bag, I see this as purely a positive thing. The ergonomics of the GH1 and GH2 left quite a bit to be desired. The layout is rather cluttered, and it is easy to press a button by a mistake. The GH3 is going to be much easier to handle, especially with a large lens.
On the flip side, one could argue that the whole purpose of the Micro Four Thirds system was compactness. So why introduce a larger flagship model?
The GH3 deviates from the predecessor GH cameras in a significant way: It no longer offers the oversized, multi aspect sensor.
With the multi aspect sensor, the GH1 and GH2 could take photos at 4:3, 3:2 and 16:9 aspect ratios while retaining the same diagonal field of view. This has the advantage of utilizing the lens imaging circle better. More importantly, it could record videos at the 16:9 aspect ratio while retaining the same field of view as well.
Without this feature, the lenses effectively lose some wide angle feature when switching to video. It means that the wide angle property that you were used to when using the GH2 are going be a bit disappointing when switching to the GH3. The difference is not too significant, but noticeable.
When using a fisheye lens on the GH2, for example, you get a 180° diagonal coverage in both photos and videos. With the GH3, though, you get the 180° diagonal field of view only in the 4:3 still image mode, and less than that in video mode. This applies to the Samyang 7.5mm f/3.5 fisheye lens for example.
The GH3 takes the Micro Four Thirds system into the professional territory: With better ergonomics, splash protection, better video bitrate and connectivity. Sadly, it also comes at a significantly higher price point.
While it doesn't live up to all the expectations people had, I am confident that the GH3 will be loved by the users.
Those who are put off by the size increase could still look to the Panasonic G5. While it does not offer quite the same feature set as the GH3, it is still a quite impressive camera given its size.