Autofocus

Nikon has developed an all-new hybrid AF system for its two Z-series cameras that is responsive and accurate, though there are a few foibles and Nikon DSLR users may find some familiar features missing.

Key takeaways:

  • AF speeds are excellent in good light and fine most of the time in low light
  • The subject tracking implementation requires too many button presses to be usable, making it more cumbersome than Nikon DSLR 3D Tracking. It's also less reliable.
  • The camera tracks approaching and randomly moving subjects very well when using continuous AF and a manually chosen zone or AF point
  • In Auto Area mode, the Z6 may have difficulty refocusing on another subject if it's previously been locked on something in the foreground or background
  • Face detection in low light is effective and works with subjects wearing glasses, which is a pleasant surprise. While there's no Eye AF, Nikon has confirmed that it will be added via firmware.

The Z6's AF system is much like that of the Z7's, just with fewer points. It works differently than Nikon's DSLRs in that the AF modes are different, selecting a subject to track is cumbersome and an equivalent to the company's famed 3D Tracking feature is nowhere to be found. We dedicated an entire page in our Z7 review that goes covers the differences in usability between that camera and Nikon's DSLRs, so have a read for more details, particularly around why engaging and using subject tracking is problematic.

AF-C performance

To test continuous AF performance, we first try to shoot a subject approaching at a steady speed using the central AF point. This lets us see how good the camera is at assessing subject distance and whether it can drive its lens to that point quickly. In the example below we used an adapted Nikon 70-200 F2.8 ED VR II lens.

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The Z6 performed extremely well in this test, with a nearly perfect hit rate through numerous runs at 5.5 fps, which is the fastest speed with both continuous focus, exposure and live view (you can shoot at 9 fps as well, though you lose live view).

We then have the subject weave across the camera's AF region in a way the camera can't predict. This has the advantage that the approach rate varies as the subject changes direction. For this test we use the camera's subject tracking mode, so it needs to identify and follow a subject around the scene, as well as trying to keep it in focus. The only AF mode in which you can specify a subject to track is Auto Area. You can choose your subject via the touchscreen, joystick or four-way controller.

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Generally speaking the Z6 did an excellent job tracking Richard as he weaved toward the camera. The AF point wasn't always on top of him, but the camera still nailed the focus. There was one run where the Z6 lost him and focused on the background, but it eventually re-acquired him and focused correctly from then onwards.

After extensively testing the Z6 we noticed some frustrating quirks with the AF system. The most bothersome was how, in Auto Area or subject tracking modes, the camera was very slow to refocus on new subjects after it's been focused on something in the foreground or background. Even if you take your finger off the shutter release, recompose, and half-press again, it is reticent to refocus. Even if the focus points were sitting on top of the new subject, the Z6 might not refocus. This didn't happen every time but occurred enough to cause missed shots.

Something else we observed is that there's occasional 'jitter' as the AF is trying to lock onto low contrast subjects. This was mainly an issue using continuous AF; the camera was more decisive using single AF. Backlit situations consistently caused hunting and misfocus in any AF area mode, so if backlit portraits are your thing, there are better performers out there.

Fast action

We wanted to see how the camera performed for fast action, so tried it out in two different situations. First, we went to an 'Extreme Air Sports' venue in California to see how the camera did with a (very) fast-moving child on ziplines and obstacle courses. When the subject really stood out from the background, the camera was able to track them. Most of the time, however, the camera latched onto the background and stayed there. Subject tracking simply wasn't reliable consistently in the real world, and given how cumbersome it is to use anyway, we found ourselves missing Nikon's '3D Tracking' available on its DSLRs.

Cropped to taste | ISO 640 | 1/800 sec | F2.8 | Nikon 70-200mm F2.8G ED VR II @ 70mm
Photo by Jeff Keller

The second thing we tried was shooting an 'ultimate frisbee' match using an adapted 70-200 F2.8 lens. Unlike the previous example, where there was time to tap on a subject to track, we specified an AF area (Dynamic mode) and kept the camera pointed at the subject. Generally speaking, the Z6 did quite well at refocusing as we followed the subjects around the field.

When it missed, it was almost always because the focus point was no longer on the subject. Even at 5.5 fps with liveview, the EVF refresh is a bit laggy with significant blackout between updates, making it difficult to see to where your subject is at any given moment. That makes it hard to keep your focus point over the subject consistently as it moves around the frame. This is where subject tracking can be immensely useful, but again we don't find it reliable or usable enough on the Z6.

The Sony a7 III handles this much better, fading to black in between live frames - at a faster frame rate no less. This gives more of an impression of continuous subject movement, making it easier to follow the action. The Nikon holds a live frame for a few frames, then immediately switches to a black frame for many frames, leading to a jarring blackout experience that makes it hard to follow action. It's not much easier to follow action in its H+ (9/12 fps) drive mode either, since that's just a slideshow of last-shot images.

Low light AF

Nikon claims that the Z6 can, with an F2 lens, focus at light levels as low as -2EV in 'normal' mode and -4EV in 'low light mode'. (By comparison, Nikon's D750 focuses down to a claimed -3EV, and the EOS R down to approximately -4.5 EV with an F2 lens in our tests.)

In low light with F1.8 primes, Sony's a7 III focuses a bit faster and more confidently than the Z6, with reliable Eye AF in those conditions. This is true both in AF-S and AF-C. As light levels dropped further, performance between the two cameras evened out. With F4 lenses the Z6 had a slight edge. As you'd expect, the Z6 performed better with the faster F1.8 lens than the F4. Regardless of the lens we tried, we found the Z6 to be more responsive and accurate at focusing in low light than its big brother, the Z7.

In extremely low light, if you've turned it on, 'low light mode' activates (in AF-S), and when it does you'll notice it - there's a noticeable drop in EVF refresh rate, and focus slows down, a lot. However, the mode can allow the camera to lock onto static subjects in very dim conditions... eventually. However, it's so slow in real-world use to be impractical.

The test below aims to simulate a social event in dim lighting. In the example below we put the camera into Auto-Area AF mode and used both face detection at a burst rate of 5.5 fps. Our lens of choice was the 35mm F1.8 S.

The Z6 did a pretty good job in this test, with the rare ability to detect the face of a person wearing glasses. While the concept of being able to use the four-way controller or touchscreen to switch between faces is nice, in reality it didn't work all that well. That's because all it takes is for one of the subjects to look away and you lose the option to select it. The experience ends up feeling like a video game, trying to hit the arrow key as quickly as the camera provides the option, just it case it disappears again.

It's worth noting again that while the Z6 doesn't offer Eye AF like several of its peers, Nikon is working on a firmware update to add that useful feature.

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