Autofocus

The a7R II features the latest iteration of Sony's continuously evolving autofocus system, in this case an implementation that uses both on-sensor phase detection (for depth awareness) and contrast detection autofocus (for high precision).

On-sensor phase detection means that the camera can be both fast and precise, even when shooting with fast glass and very little depth-of-field, and even when you combine these with fast walking motion.

Zeiss Batis 25mm F2 | ISO 2500 | 1/500th, F2

Although DSLRs have traditionally offered the best autofocus performance, the results of these on-sensor technologies have improved rapidly and now challenge DSLR supremacy in many (though not yet all) respects. The great advantage that on-sensor systems have is that they are assessing focus from the same point that the image is being captured from. This means they have none of the cummulative errors introduced by manufacturing and alignment tolerances that can build up in DSLR autofocus modules, where focus is measured by light diverted via a secondary path to a separate sensor. Residual spherical aberration of lenses can also severely throw off DSLR focus systems, and appear to have less of an impact for most on-sensor AF systems.

Although some of these errors can be overcome by AF fine tuning, these rarely have the complexity necessary to correct for the many variables that can contribute to the problem (variation between focus points, differing results at different focal lengths or subject distances, impact of lighting color...). Practice supports the theory that focus measured at the imaging plane is a more consistent way of ensuring good results - something that is particularly important with a high resolution camera that will reveal any slight mis-focus.

AF options

Sony's broad range of AF options can be daunting but also rewarding. There are five different focus area modes (Wide, Center, Flexible Spot, Expand Flexible Spot and Lock-on AF). Within this, the Flexible Spot mode, where you manually position the AF point, offers three AF point sizes. Meanwhile, Lock-on AF, which can only be used in continuous AF, offers all other AF area modes as sub-options, so that you can decide the most appropriate means of initially selecting the object you want it to track. We've found, however, that changing the size of your AF point in Lock-on is virtually useless, as it appears to be largely ignored by the Lock-on algorithm and doesn't force it to be more or less specific when you use smaller or larger AF points, respectively.

On top of this, there's Face Detection mode, which is selected separately. This will indicate any faces that the camera has detected in the scene but the camera will only focus on these faces if your chosen focus area mode overlaps with the face. In other words, an off-center face won't be prioritized over the subject in the middle of the frame if you're in Center AF area mode, for instance. If you do want a face prioritized above all else, Eye AF - assignable to a custom button - overrides all else and will focus on an eye anywhere in the scene, though again it will prioritize one nearest your selected AF area. There's also an option to teach the camera specific faces, which it will then prioritize over unknown faces.

The a7R II offers five main AF area modes, along with Lock-on (tracking) versions of each mode.

On top of these are the Face Detection and Recognition options, an Eye AF mode and, presumably for video use, a separate Center Lock-on AF function.

It's worth learning how these interact with one another.

As we alluded to above, an additional option is Eye AF, now available in continuous AF mode, which is operated separately from all the other AF settings. You'll need to assign Eye AF to one of the camera's customizable buttons to use it. In AF-C mode, pressing this button will find and follow the eye nearest your selected AF area or, if no specific area is selected, the eye nearest the camera. In AF-S mode, it will highlight an eye for around 1 second as the eye is focused on. Eye AF does not require Face Detection to be engaged to work.

Center Lock-on AF: a vestigial function

Just to add a further level of complexity to proceedings, the camera still offers Center Lock-on AF as a separate function (not to be confused with the Lock-on AF Center AF area mode, with which it's incompatible). So far is we can tell, this is a vestigial feature that dates back to before Sony got the Lock-on AF area mode (triggered with a half-press of the shutter button) worked out. The Center Lock-on AF function is locked onto a subject by pressing the central button on the back of the camera and presumably remains in the camera because it's the only tracking AF mode available while in movie mode. It's a cumbersome, inefficient way of working compared to Lock-on AF which is triggered by a half-press of the shutter, so it's inexcusable it remains, and more so given it's the only way to enable generic subject tracking in video.

Autofocus performance (Native lenses)

Most contemporary autofocus systems can very quickly focus on a static target and autofocus speed itself is not an issue for the a7R II. The a7R II is incredibly fast at initial focus acquisition. The more interesting question is: how well does it take advantage of the depth information provided by its on-sensor phase detection elements, particularly for continuous AF?

To test this, we walked towards our test scene, shooting in continuous drive mode (5 fps, center point) with AF-C engaged. We conducted the same test with the Canon EOS 5DS to get a sense for the level of performance you should be able to expect.

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The performance is remarkable for most of the run: almost every image is in focus despite constant movement, save for the last few. At closer distances the hit-rate clearly drops off but overall performance is broadly comparable with the Canon EOS 5DS's results that we show later in this review.

We also shot one of our standard tests to see how well the a7R II copes with changes in depth over relatively long distances (something DSLRs have traditionally excelled at), tracking a cyclist riding at a moderate speed directly towards the camera. Read on below.

Center Autofocus Area

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We shot our cyclist at 5 fps with a Sony 70-200 F4G OSS lens, using the center point in AF-C. On the whole, the camera does respectably well - most of the shots are in perfect focus, with only shots 3, 13 and 14 noticeably less than perfect.

We're finally at that inflection point: where mirrorless on-sensor phase-detect AF (PDAF) is seriously challenging DSLR dedicated phase-detect modules, if not exceeding their performance due to obviating AF calibration requirements. That said, on-sensor PDAF is still not optimized at making measurements from extreme defocus like DSLRs; hence, though we didn't experience any during our cycling test, you will get hunting from time to time. Birds-in-flight and sports photographers will still benefit from the instant, decisive focus DSLRs provide even when starting from a completely defocused, blurred starting point.

Autofocus tracking performance

Having established that the a7R II does pretty well at interpreting changes in depth, we added an extra variable to the test: moving in the X and Y axes to see how well the camera would track the subject (rather than simply refocusing in the same place).

This test is intended as a simplified model of, for instance, a small child running across a lawn in an unpredictable manner but conducted in such a way that we can use it to test multiple cameras in a reasonably repeatable manner. In this first instance we set the camera to 'Wide Area' AF, with the camera selecting the subject, then trying to stick to it.

Wide Area Autofocus

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The results are very impressive: although a couple of shots aren't perfectly focused, all of them are pretty usable and a good number show the camera's full resolution benefit (which is no small matter on such a high-res camera). Click here to see the video feed from the camera, showing what it was focusing on. As you can see in the video, the camera's subject tracking system, which in this case uses distance information to understand and follow the camera's initially chosen subject, does a really good job of sticking with our cyclist.

The reality, though, is that 'Wide' AF area is of limited use: most photographers desire to define their subject themselves, not have the camera choose the subject. You can designate your initial subject, but have the camera track it thereafter, using 'Lock-on AF', which itself has number of different AF area modes you can select to define your AF point(s). We tested Lock-on AF: Center below.

Lock-on Autofocus

Sony's Lock-on AF attempts to identify the subject that you've initially specified then stick with it, wherever it moves in the frame. It does this using color and pattern recognition based on the information from the imaging sensor (presumably with depth information from the camera's phase-detection elements). This should, theoretically, lead to more accurate subject tracking than the predominantly depth-based methods used on traditional DSLRs. Click here to watch a video demonstrating the difference.

While Lock-on AF certainly has its value when it comes to tracking and keeping moving subjects in focus, as well to track a subject as you focus-and-recompose so you don't have to manually reposition the AF point, it's not without its issues. While it sometimes can, it often doesn't, live up to the consistent, reliable, pinpoint accuracy we're used to with Nikon full-frame DSLRs. We take an in-depth look below.

We also put Lock-on AF to the test in our cyclist test to see how it performed in real-world tracking of a moving, weaving long-distance subject. See how it did in our rollover below, and get an idea of its performance in this video footage we captured of the camera in action.

As you can see in the video linked above, prior to actually shooting in continuous drive, the camera's understanding of the subject is quite good, exemplified by the green square that sticks with our cyclist as he moves forward and weaves. However, almost as soon as the camera starts shooting, it drops out of subject recognition mode (Lock-on AF) and tracks the subject solely based on depth information (the small green squares), similar to the 'Wide' AF area we tested above. You can see this switch from Lock-on to depth-based subject tracking in our aforementioned video; note the large green subject box (Lock-on AF) replaced by a series of dancing squares (phase detection) just after the screen blacks-out in this video.

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As we'd seen in 'Wide' area AF above, results are pretty successful: not surprising since the 'Wide' and 'Lock-on' end up using similar depth-based methods during a burst. However, not all shots are focused. Furthermore, in our real-world testing, Lock-on AF itself isn't as reliable as we'd like it to be: we often found the camera will lose the subject. And that's before you consider the fact that Lock-on itself shuts off entirely in continuous drive, reverting to depth-based subject tracking - a method fallible to jumping off to the wrong subject, as we show in our video and as we've experienced with DSLRs operating similarly off of only depth information (like the Canon 5D Mark III). We wish actual pattern-recognition based subject tracking was maintained during continuous drive, like Eye AF and face detection are.

To be fair though: subject tracking during continuous shooting is something even most DSLRs struggle with, with Nikon full-frame DSLRs offering arguably the most robust system.

What we noticed with Lock-on reverting to a simpler tracking mode is something we've seen before: a number of mirrorless cameras can track a subject pretty well but the performance drops during continuous shooting, where the camera expends considerable processing power processing images and writing them to the card, and also experiences constant blackouts as the shutter is activated and sensor read. This is all consistent with the a7R II's inability to re-engage Lock-on AF when the camera is writing to a card - it appears the algorithms are very clever but require more processor power than the Bionz X can summon up. Try it: as the camera is clearing its buffer, Lock-on will initially engage, but will quickly revert to depth-based tracking (the little green squares) as soon as there's movement or you recompose.

What about sports?

In addition to the comparatively repeatable tests shown here, we also subjected the a7R II to some challenging real-world usage, and put the camera in the hands of a professional shooter pitch-side at the Seattle Seahawks. As you might expect, the a7R II performed significantly less well when trying to keep track of faster moving subjects during continuous shooting, and where there was a multitude of visually-similar potential targets. But not necessarily due to an AF system that can't keep up.

The reality is that these situations will stress even the best automatic subject tracking systems, and though the very best may perform better (Nikon's 3D tracking), many pros will revert to single-point AF. And here's where the a7R II struggles: (1) keeping the AF point over your subject precisely amidst EVF/LCD blackouts is difficult, and (2) repositioning the AF point quickly as the action changes without direct access to AF point selection via a dedicated joystick or D-pad is cumbersome. So while the AF performance is formidable, the success of the camera as a whole can be situation-specific, and we wouldn't recommend the a7R II over a traditional DSLR for continuous bursts in sports scenarios. It's simply too difficult to keep your subject in the frame, or the AF point over the subject, during continuous bursts. This is simply a reality of current mirrorless systems' inability to provide a live feed of the action during bursts, and not a reflection of the AF capabilities of the camera.

Does that mean the camera can't successfully shoot action/sports? Not necessarily. For example, in this simpler yet fast-paced scenario with a number of breakdancers in a water ring - where I could leave the camera in 'Wide' AF area mode and allow it automatically identify and track the main subject -  the camera performed admirably. Again, success is situation specific, so while this won't be your go to camera for sports shooting, you may still experience a certain degree of success in some cases.