AF Review: 7D MK2 vs NX1 vs GH4

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Action photography was the exclusive domain of the SLR.

Action photography, a bit over a year ago, meant that you used an SLR on continuous AF and burst mode. And then took shots at around 5 images per second. When I took pictures for CameraStuffReview with an SLR camera (or a Nikon 1) of a speeding car that was coming right at me, then with a series I got primarily sharp—and a few less sharp—shots. Phase detection of an SLR camera, since the appearance of the Minolta 7000 in 1985, has grown into a lightning-fast system.

01AFtest

Phase-detection AF is also able to anticipate the direction of movement of the subject. Compact cameras and many compact system cameras make use of contrast-detection AF, which was clearly slower. And this system needs time to establish the direction of movement of the subject. Until recently, contrast detection was too slow to follow a moving subject.
In 2015, there are system cameras with fast contrast detection (see the GIF animation in our Panasonic GH4 review), system cameras with lightning-fast hybrid AF (Nikon 1) and system cameras with phase detection on the sensor (Olympus E-M1 and Samsung NX1). The best compact system cameras and SLR cameras take 10 to 15 shots per second in full resolution. If you only photograph in jpg, they can keep that up for a very long time. These are important improvements for action photographers.

Practically all reviewers—including me—say that for action photography—in contrast with photographing a static subject—the SLR has a lead on compact system cameras.

How great is that lead for action photography? I know very few tests where AF systems have been compared directly with each other in practice when making action photos. In a continuous AF test by Traumflieger, the continuous AF of an SLR with 10 images per second and two system cameras (with 7 and 15 images per second) are compared with each other in practical situations.

Single-shot AF: suitable for standing still and moving?

01AFtest2

Nikon V3 + Nikon 70-200 mm f/2.8 (via FT1 adapter) @ 200 mm f/5.6 1/500 sec

The accuracy and the speed of AF will typically be tested in the single-shot mode, and not in the continuous AF mode. That is not illogical, because single-shot AF will also be used much more by photographers. A few years ago, when taking a single picture, the phase detection AF of SLR cameras was faster than the contrast detection of compact system cameras. On the other hand, the reproducability and accuracy of system cameras, which focus on the sensor signal and therefore are not bothered by front or back focus, was difficult to match with SLR cameras.
Where we "previously" wrote for an AF test that the AF of an SLR camera was fast because the lens could focus within a second and a half from infinity to close-up, there are now SLR cameras and compact system cameras that focus in milliseconds. And—when you have corrected shots from an SLR camera for any front or back focus—all modern AF systems are reproducibly accurate when it comes to focusing on a static subject. It might surprise you how often you can get a sharp photo of a moving subject—racecars and the like excepted—while the camera is set on single-shot AF.

Continuous AF test: AF for a moving subject

If, however, you want to take multiple shots right after each other, then you are better off switching to continuous AF and the burst mode. In a video more than 20 minutes long, Traumflieger shows how they carried out different AF tests for a moving subject. You do not have to be able to understand German in order to understand the video. The images speak for themselves:

  • For the AF test with a slow-moving subject, someone who is walking towards the camera, the continuous AF of the Panasonic GH4, Canon 7D MK2 and the Samsung NX1 do about equally well; some 95% of the shots of a moving subject are sharp. All three of the cameras are tested at f/2.8 and the same field of view, corresponding with 300 mm full-frame equivalent. The cameras took pictures during this test in RAW + jpg, whereby you can hear that the Samsung NX1 (which has one-and-a-half times as many pixels as the Canon 7D MK2 and twice as many as the GH4) was not tested at its maximum speed of 15 images per second because otherwise the buffer of the camera would fill up too quickly during the test and the number of images in the second part of the test (when the person comes close to the camera) would be much lower than at the start of the test.
  • In the AF test with a fast-moving subject, a driving car that comes towards the camera in bad weather (pouring rain) and low light, is the toughest test for these three cameras, not only because the subject is moving much faster, but also because the AF of all the cameras focuses more slowly in low light. Here, the differences in AF quickly became apparent.

Runner up: Panasonic GH4 (with Olympus 40-150 mm f/2.8)

GH4 back700

Bokeh or focal depth?
Rather a running cheetah that is sharp from head to tail than sharp from tail to body.

Under poor lighting conditions in the pouring rain, the Panasonic GH4, with the Olympus 40-150mm f/2.8 in the burst mode and continuous AF (7 images per second) was on target for 73% of the test shots. For reviewing SLR cameras, it's not long ago that I would have pinched myself over a score like that. But there are also footnotes. In contrast with the Samsung NX1 and the Canon 7D MK2, the Panasonic GH4 at f/2.8 has greater focal depth. The tester correctly notes that the Panasonic GH4 has 1 stop more focal depth under the selected testing conditions, so that it's a bit easier to get a sharp picture. Sometimes, action photographers can consider themselves lucky with a smaller sensor. For the same reason, I'm charmed by the Canon 7D MK and the Samsung NX1, but then in comparison with full-frame cameras.
Perhaps the AF of the Panasonic GH4 would be even a bit faster if the Panasonic 35-100 mm f/2.8 had been used, because the Panasonic GH4 only makes use of Depth from Defocus (DfD) when used in combination with Panasonic lenses. The AF of the Panasonic GH4 puts on its best performance where AF speed is concerned when you use a lens with which DfD can be applied (read: only Panasonic lenses). Because the Traumflieger testers carried out the AF tests in all three cases at f/2.8 and a field of view corresponding to around 300 mm, converted to a camera with a full-frame sensor, the maximal focal distance of the Panasonic 35-100 mm was too short to use this lens in the AF test.

Surprisingly good second: Samsung NX1

NX1

77% on target at 15 images per second;
averaging 12 sharp pictures per second

The Samsung NX1 is heavyweight in the test, when it comes to specifications. First, this camera has the largest number of megapixels. In addition, the Samsung NX1 is one-and-a-half to two times as fast as its two competitors. That places heavy demands on the image processor that has to process all this information, even moreso because the AF also uses the sensor signal. That's why the test with the moving car was only carried out with jpg files, so that the camera could carry on making 15 images per second. Of the 379 test shots made at the unprecedented speed of 15 images per second, 87 were blurred. That's an average of 3 blurred and 12 sharp shots per second.

AF test winner: Canon EOS 7D MK2

Top performance: on average, 8.4 out of 10 fps are sharp

The action photography test by Traumflieger was won by the Canon 7D MK2.
84% of the action shots were sharp. Rounded off, you get an average of 8.5 sharp and 1.5 blurred shots per second. The Canon 7D MK2 has the same AF system as the Canon 1DX, Canon's professional top model for action photography. The smaller sensor of the Canon 7D MK2 offers (compared to the Canon 1DX) a greater focal depth at the same field of view and the same aperture. I would not be shocked if a Canon 7D MK2 at 200 mm and f/2.8 delivered even more sharp pictures during action photography, due to the larger focal depth, than a Canon 1DX at 300 mm f/2.8.

Design Cut EOS 7D Mark II 2 W Special
Hats off to the Panasonic GH4 and the Samsung NX1
For the same reason, I expect that the AF of the Canon 6D, in a test at the same field of view and the same aperture, would perform more poorly than the—also much more advanced—AF of the Canon 7D MK2. That means that there will be a great many SLR cameras that do worse with action photography than the Canon 7D MK2. Because the Panasonic GH4 and the Samsung NX1 score nearly as well in this test as the Canon 7D MK2—and in the first part of the test, just as well—the difference in speed of these system cameras compared to many other SLR cameras is even smaller. Hats off.

End of SLR supremacy, even for action photography?

Too long, didn't read (TL/DR): AF of compact system cameras is fast enough for action photography, as it appears from a practical test of continuous AF.

If you want to get started with action photography, do not expect that you will immediately score more than 80% successful shots. Action photography is a specialty, where experience counts. Traumflieger justly notes that the number of successful shots for all three cameras would be lower if you were photographing under more difficult lighting conditions than those under which the AF test was carried out. They also admit that if you process the test results statistically, the difference in AF speed between these three cameras might not even be significant. That would mean that you would not notice any difference in practice when doing action photography where the AF speed is concerned between a system camera and one of the fastest SLR cameras available today. For the test situation with approaching cars, that's probably true. But when a subject moves less predictably than a moving car, then the most advanced SLR cameras are more accurate than a system camera.

CameraStuffReview has reviewed the Canon 1DX, Nikon D4S, Nikon D750, Nikon V3 (not yet published), Canon 7D MK2, Panasonic GH4 and the Samsung NX1 in practical tests, but not in a direct comparison like Traumflieger did. Based on our practical experiences, if my income depended on action photography, I would prefer a Nikon D4S, Canon 1DX or 7D MK2. However, if you—like me—do not have years of practical experience with action photography, then the number of "misses" will sooner be caused by the photographer than the camera, regardless of whether that's a system camera or an SLR. The Nikon V3, with its fast hybrid AF (only the buffer could be larger), pleasantly surprised me during the TT in Assen: I did not know that I was so good at action photography.

A little over a year ago, I did not believe that fast and compact system cameras would appear that, like the Samsung NX1, could deliver sharp action photos (of 28 megapixels) at 15 fps. The SLR had an answer ready with the Nikon D750 and the Canon 7D MK2. If you asked me now, then I would have to say that I expect that the supremacy of the SLR for action photography will last a few more years.

It could be that I'm proven wrong within a year.

Ivo Freriks
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.

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