Autofocus

The Multi-Cam 20K autofocus module in the D5 and D500 made waves when the cameras were announced because it offers the most autofocus points ever seen in a DSLR to date: 153 total points, 99 of which are cross-type (and 55 of which are user-selectable). Understandably, the number of available points as 'cross-type' varies depending on which lens you use and its maximum aperture, so that's something you'll want to check out in the D5 user manual. As an example, if you own a lot of older AF-D lenses as I do, you're actually limited to the 45 cross-type sensors in the center of the frame.

153 AF points in all their glory, overlaid on a rough representation of how the 180k pixel metering sensor 'sees' a scene, assuming 60k pixels each per R, G, and B. The boxes represent AF points that are user-selectable, with the dots in-between representing 'helper' AF points that the camera uses for its more advanced tracking modes.

Subject tracking: what it is and why we care so much about it

Among a few other factors, autofocus performance is something that keeps buyers coming back to DSLRs. Although cameras like Sony's a6300 and a7R II have been closing the gap (and in some instances, the gap is firmly closed), fast and erratically moving subjects are still largely the domain of DSLR shooters.

For decades, SLR and DSLR cameras have had phase detection autofocus systems made of many points. These points gave these cameras impressive depth-tracking abilities, even when shooting continuously. If you could keep your chosen autofocus point over your subject, you could get a sharp shot, and indeed, a large number of professional sports shooters continue to use this method today because it just works. Since the D5 does this just as well as, say, a D3 (besides the larger spread of AF points and extra low light sensitivity), there's not much of a story to tell here, so it's not something we focused (pun intended) as much on during testing.

We tended to leave the D5 in 3D Tracking most of the time because it just works so well - despite slowing down, it still worked in lighting conditions as dim, warm and smoky as this. Processed and cropped to taste from Raw. Photo by Barney Britton. Nikon AF-S 24-70mm F2.8E VR @ F2.8 | 1/100 sec | ISO 64000

However, Canon and Nikon have both been busy making their autofocus systems much more sophisticated than they used to be. Today, instead of having to choose an autofocus point on the D5 and follow a subject yourself, you can instead initiate autofocus with a single point and watch as the D5 tracks that subject around the frame with its 153 autofocus points. How? By shifting the selected AF point automatically to stay on your subject.

Being able to let the camera do the work for you allows for you to react more quickly (you don't have to manually select a point, you can place whatever point you already have selected over your subject and start tracking), and affords you more freedom compositionally (no more focus-and-recompose; you can focus-while-recomposing). You might also find that you can shoot at a wider aperture for greater subject isolation, because you won't need the extra depth-of-field to 'cover' autofocus misses, or the focus shift inherent to the old focus-and-recompose method.

With lesser AF systems, you might be shooting at a smaller aperture to give yourself some breathing room if the camera misses slightly. In this case, the D5's 3D Tracking was so good that Rishi was enable to initiate AF with a point near the right side of the frame as soon as the biker appeared, after which the camera tracked, and continuously focused on, the rider until just the right moment he fired the shot with a strobe that afforded - you guessed it - one shot. Photo by Rishi Sanyal. Nikon AF-S 24mm F1.8.

The D5 does its tracking using an upgraded 180k-pixel metering sensor to use color information and pattern recognition in tandem with the autofocus module's depth information. The result? The D5 offers the best subject tracking we've seen in any DSLR, and indeed any camera we've tested to date. Bar none.

How well the D5's autofocus system works

Let's put it this way - from rugby to dirt biking to motocross to soccer to dimly lit concert venues, we had to go out of our way to find shooting situations that would actually trip the D5's AF system up in 3D Tracking mode (again, if you just use single-point AF and track subjects yourself, the above situations aren't challenging the AF system all that much). Basically, if you are tracking a single, distinct subject, it doesn't really matter how it changes direction or how fast it's moving. The D5's 3D Tracking will just keep up with it, with a very high hit rate. Even a subject as specific as a human eye. The automatic AF point selection part of 3D Tracking does slow down in low light, just like AF in general, but not to the point that it becomes unusable. 

Despite dim, multicolored and distracting lighting conditions, the camera nailed autofocus in 3D Tracking mode so I could easily capture this touching scene of a man and his tasty beverage. Processed and cropped to taste in Adobe Camera Raw. Photo by Carey Rose. Nikon AF-S 24-70mm F2.8E VR @ 36mm | F2.8 | 1/250 sec | ISO 32000

The D5 gains an additional customization parameter for its AF system, allowing you to select whether your subject is moving steadily or more erratically towards, or away from, the camera. This is now in addition to the 'Blocked shot AF response' parameter which ranges from 1 (Quick) to 5 (Delayed) and determines how persistently the camera sticks to your subject before refocusing to a subject in front of, or behind, your initial subject. In our experience, leaving 'Blocked shot AF response' to its default, 3, and setting 'erratic' for subject movement worked very reliably across a wide variety of shooting scenarios.

You can, of course, just use the D5 in single AF mode which will offer excellent precision for static subjects, but the autofocus system works so well that we tend to just leave it in continuous 3D Tracking mode all the time. Here's a list of the other modes offered from the user manual (along with Nikon's use-case based recommended setup for sports):

  • Single-point AF - Nikon recommends using this with stationary subjects, but if you can keep the autofocus point over your subject, it works for moving subjects as well. This tracking is only depth-based, and the point will not automatically move around to follow your subject - you have to do that yourself.
  • Dynamic-area AF - Similar to single-point in that you must move the camera to follow your subject, only the camera will focus based on information from points surrounding the single point placed over your subject, and use that information to maintain focus if the subject briefly leaves that point. How briefly is defined depends on your 'Blocked shot AF response' setting - the higher your setting, the longer the camera will continue to track your initial subject before just refocusing on whatever's under your selected AF point. There are three different area sizes available, ranging from 25 points to all 153 points, and you'll want to grow the area size as your subjects move more unpredictably (think race cars versus birds in flight).
  • 3D Tracking - The camera uses both color/pattern and depth information to automatically move the AF point to stay on a subject. In our experience, this mode works great for general usage, such as placing an autofocus point on someone's eye and then recomposing at will as the point continues to track the original spot you placed it. It also works well with erratically moving subjects.
  • Group-area AF - Also similar to single-point and Dynamic-area, the camera focuses using a group of AF points with equal priority, to reduce the risk of focusing on the background if, for example, a single point were to wander off your subject and momentarily hover over a background. This mode is also useful for when you don't have the luxury of precisely placing one AF point exactly over a subject suddenly appearing in the frame.
  • Auto-area AF - The camera will automatically detect a subject and select the appropriate focus points, and will give priority to faces and eyes. On the D5, it works staggeringly well.

Auto AF Fine Tune

The D5 and D500 have introduced an arguably ground-breaking automated procedure for fine-tuning lenses. We've already covered it in some detail, but the basic gist is that the D5 will calibrate your particular copy of a lens to itself automatically. It's got some limitations, in that it only calibrates in the center of the frame and offers no provision for multiple values on zoom lenses, nor for multiple subject distances or different lighting (daylight vs. tungsten). That said, it's a thoughtful and handy addition that addresses one of the largest shortcomings of DSLRs compared to mirrorless when it comes to focus accuracy. It's also quick enough to be done just about anywhere. No more LensAlign or FoCal apparati

AF Fine Tune OFF
(focused on nose)
AF Fine Tune ON
(focused on eye)

Click through for the full-size images. We placed a single AF point over Sam's left eye (on camera right) for focus in both cases, and Auto AF Fine Tune decided our 24mm F1.4 G needed a correction of +14 on our D5 body. In other words, this particular 24/1.4 front-focused significantly out-of-the-box, but automated AF Fine Tune fixed that right up. This is the start of something huge when it comes to DSLRs: saying goodbye to back/front-focus issues. It's not perfect - it doesn't change the AF precision of the system, only AF accuracy - nor can it correct for any miscalibrations between AF points on your camera, but it's a big step in the right direction for DSLRs.

Preferred autofocus setup

As a fan of back-button focus, I've set up the D5 to have autofocus decoupled from a half-press of the shutter button, with the AF-ON buttons engaging 3D Tracking (my main AF mode), the 'Fn1' button under my ring finger to switch to single-point AF for situations when I want to freeze the autofocus point movement but keep tracking depth, and a press of the AF sub-selectors to enable 'Auto Area.' 

For more casual snapshots, I'll still sometimes focus with the center point and recompose. The Nikon D5's touchscreen allows me to double-tap to zoom in on the face of my subject here in Image Review, instead of defaulting to wherever my AF point was if I used the 8-way controller center button to check focus in playback. Processed to taste from Raw. Photo by Carey Rose. Nikon AF-S 35mm F1.4G | F1.4 | 1/200 sec | ISO 100

What's really cool is that in this setup, I can hold down AF-ON for 3D Tracking, but temporarily disengage automatic AF point selection to freeze my AF point - but continue focusing - by holding down the Fn1 button. When I want the camera to re-start subject tracking (automatic AF point switching to follow my subject), I just let go of the Fn1 button. Lost my subject but need to nail the shot in a fraction of a second? Just jam the AF joystick to enable 'Auto Area' and hope my camera automatically picks up on my subject or a face in the frame. This doesn't always work, but that versatility can make or break a shot.

For more on how this setup applies in real life, let's head to a motocross practice session on the next page.