Autofocus tracking

Processed to taste in Adobe Camera Raw. Nikon 70-200mm F2.8E
ISO 64 | 1/2000 sec | F2.8

We've already written a lot about subject tracking and Nikon's 3D Tracking in particular. In spite of other cameras on the market perhaps offering more frames per second, more autofocus points, or both, we continue to find that the 3D Tracking implementation on the flagship D5 is still the best overall performer in terms of focus accuracy and tracking reliability. It's remarkably reliable at automatically shifting the AF point to stick to your original subject.

But the D850 is not a D5, it just shares the autofocus system. So, we set it up in front of a man on a bicycle to find out how it copes with semi-quick, non-predictable (for a camera) subject movement.

Bike test

As with all Nikon DSLRs these days, the D850 performed near-flawlessly with a rider coming straight at the camera, continuously autofocusing with a single point over his face. So no surprises there - but we were surprised to find some issues with the D850's 3D Tracking when the cyclist was weaving side-to-side.

As with all Nikon DSLRs these days, the D850 performed near-flawlessly with a rider coming straight at the camera

While the rider coming straight at the camera assesses whether a camera is able to deal with depth information and asses whether the camera can even drive the lens' focus elements fast enough to keep up, introducing the weave necessarily introduces greater stresses on the camera. It must be both reactive and predictive in an effort to keep the proper autofocus point on the subject.

And in many instances, the camera was able to correctly recognize and follow the subject around the frame which, combined with the ability to judge depth and drive the focus quickly (that we saw in the straight-on test), gave a very good result.

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Now this isn't a bad show considering the amount of lateral movement, with a lot of movement towards the camera, at seven frames per second and 46 megapixels. However, without any rhyme or reason, this would sometimes happen:

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The D850 would sometimes, mid-burst, lose track of the subject it had initially been tracking. This happened both in the middle of the autofocus area, as above, and also near the edges (usually at the apex of a turn, indicating a change in approach speed to the camera). It happened regardless of whether the camera's 'Subject Motion' parameter of 'Focus tracking with lock-on' was set to Erratic, Steady, or in-between.

And this didn't happen overwhelmingly often, or with any regularity - there were times, such as when Dan was backlit by car headlights, that I expected the camera to get distracted, and it didn't. We also swapped the D850 out for a D5 and ran the same test with the same lens three times, at 12fps, without any such problems. The D850 exhibited this issue within the first three runs on two testing occasions.

In any case, the story with autofocus tracking appears to be similar to that involving autofocus precision; the D850 is certainly capable of tracking extremely well, but there appears to be some other factor(s) at play holding it back.

Low light autofocus

One of our favorite use-cases for 3D Tracking, or subject tracking in general, is candid, social photography. Allowing the camera to track your subject while you freely change your composition can come in very handy - when it works.

With the D850, we're happy to report that there weren't any egregious focus errors such as what we found in our bike tests. However, we have found both in this test and our less structured observations while using the camera, that the autofocus point seems more prone to 'jump around' our initially chosen subject, rather than sticking tenaciously to the exact point on that subject at which autofocus was initiated.

Granted, we are comparing here to the flagship D5, though the D850 still performs far better than some competing brands in this regard, including Canon's iTR or Intelligent Tracking and Recognition.

It's also worth mentioning that the AF point is hard to see in low light or low contrast situations. When tracking the black point is often difficult to make out, and even when the camera flashes the selected AF point red when you initiate, it's not very bright. The brightness is adaptive: brighter in bright light and dimmer in dim light, but we'd rather prefer it to always be bright, as can be enabled on Nikon's flagships.

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Appropriately for a highly capable camera, the D850 comes with a highly capable autofocus system. In single-point Single AF and Continuous AF, as well as in its Dynamic area settings, accuracy, hit rate and precision all rank pretty high. However, the D850's massive resolution shows up some inherent issues in terms of how DSLR autofocus systems work that might prevent you from getting all 'keepers' all the time, especially if your lens requires calibration. This shows up most often in wide-aperture work, such as some styles of portraiture, where autofocus precision is of paramount importance.

In terms of subject tracking, we continue to be perplexed by our experiences with 3D Tracking - but we must admit that, during burst shooting, the D850 pulls away handily when compared to its predecessor, the D810, as well as the Canon 5Ds R and Sony a7R II (though the Sony tracks better in Eye AF mode as long as you're not shooting bursts). However, despite Nikon's claims of D5 levels of performance, we collectively find the D850 to be somewhat lagging behind that lofty benchmark.

We'll be reaching out to Nikon with our observations, and have procured a battery grip for the D850 that boosts shooting to nine frames per second and provides a boatload of extra shots per charge. There's an awful lot of sports shooting in our D850's future, so stay tuned for updates.