How fast is the continuous AF of the Panasonic GH4?
We're working on the write-up of our Panasonic GH4 test, in which we focus on the improvements the GH4 includes over the GH3. One of the most noticeable innovations, after 4K video, is the improved usability for action photography.
The AF of the GH4 (and GH3) is sublime for static subjects. With moving subjects, the GH4 beats out the GH3 with AF. In addition, the shooting speed is increased. The GH4 sensor is lightning-fast, and the camera is able to keep that up through many shots, thanks to a large buffer and high write speed – ideal for action photography. We took the GH4 along to a bird show. Birds flying fast overhead from a relatively short distance makes, not only for the camera, a more difficult subject than athletes or cars from somewhat further away.=.
Contrast AF with DFD Technology for fast series shots
Panasonic GH4 + Panasonic 35-100mm f/2.8, continuous AF with 7.5 RAW + jpg shots/second @ 1/2000 sec, 200 ISO, f/2.8. Image excerpt (30%) of a fast overflying - flying, not gliding - Harris' hawk.
DFD ("depth from defocus') technology
The continuous AF of the Panasonic GH4 makes use with moving subjects of the bokeh character of Panasonic lenses, which is stored in the camera. On the basis of that, the Panasonic GH4 can calculate from two images (far and closely focused) the approximate distance where the subject is located. This is called DFD ("Depth from defocus"). The picture here, borrowed from the Panasonic website, illustrates what happens: With conventional contrast AF, the subject is followed in small steps, that are shown with the blue line. Fast moving subjects are already gone, before you've gotten a sharp image.
With DFD, the Panasonic GH4 calculates how far the subject is removed. The AF motor then makes a big jump, shown in red on the Panasonic illustration, in order to then focus precisely with contrast AF. From this, the Panasonic GH4, when using Panasonic lenses, is the fastest micro-43 action camera.
Don't expect that the continuous AF of the Panasonic GH4 will beat out a professional camera like the Canon 1Dx for action photography. It is certainly a huge leap forward for photographing fast-moving subjects with a contrast-AF camera. You come home – in my case – with a lot of failed pictures. The experience of the photographer with action photography as well as the small size and high speed of the subject play an important role here. The good news is this: there are now many more successful shots as well – even of difficult-to-follow subjects!
Panasonic GH4: 12 (RAW + jpg) bps with AF-S and 7 bps with AF-C
With 12 bps (S-AF) or 7 bps (C-AF), where both RAW and jpg files are saved, the performance of the GH4 is comparable to better SLR cameras. In the picture here, the Panasonic GH4 uses continuous AF to follow a small bird, which in the first picture (right) is not yet in focus and in the second picture (left) from a series made with C-AF is already nearly sharp. In the first picture, the trees are sharp and the bird is completely blurred. In the second picture, the trees are completely blurred, because the Panasonic GH4 focuses on the bird. It's going so fast that in the next picture I no longer had the bird in the AF window.
Click on the image to the right for a larger version (expanded to 100%).
Panasonic GH4: 40 shots per second
I'm not an action photographer and photograph almost always in the single-shot mode. And I expected that 5 shots per second would be more than enough for practically all action photos. From testing, I discovered that some, even everyday, subjects are so fast that even 12 shots per second is not enough – a sparrow that flies away, for example. Because the buffer of the Panasonic GH4 is particularly large, you can anticipate the moment that the sparrow takes off.
If you want to be even faster, you can save 40 jpg images per second in a lower resolution (2336 x 1560). You focus in advance – because with such extremely high shooting speeds, there is no interim focusing – and then press the shutter before the bird flies away. You can be a couple seconds too early; the buffer of the Panasonic GH4 is big enough. You just throw the extra shots away. At 40 images per second, the sparrow is still completely still in image 0, and the sparrow is completely out of frame in image 4. Below are the three interim shots, made with a 400 mm focal distance (comparable with 800 mm @ full frame). At a speed of 8 shots per second – there are many SLR cameras that are less fast – you only shoot 1 image in the same timeframe. The chance of a successful shot is then small.
Another tactic is to switch to video, with which you manually set a fast shutter speed. If you use the Panasonic GH4 video in 4K (4096 x 2160), then you shoot 30 frames at 8 megapixels per second. From the resulting video frames, you choose the best image for a beautiful print on A4. Photographing with 4K appears in our Panasonic GH4 test, which will appear soon.
Author: Ivo Freriks
With Camera Review Stuff I hope to make a modest contribution to the pleasure that you get from photography. By testing cameras and lenses in the same way, evluating the results and weighing up the pros and cons, I hope to help you find the right camera or lens.