Autofocus and performance

Out-of-camera JPEG.
Sony 18-135mm F3.5-5.6 | ISO 6400 | 1/500 sec | F5.6

Sony has made great strides in autofocus performance with the a6400 thanks to the new 'Real-time Tracking AF' implementation, which seamlessly transitions from subject tracking, to face detection, to Eye AF and back again. Though we are really impressed with how well it works, we think it's time for Sony to clean up some of its autofocus options, many of which are redundant (and have been for some time). A noticeable boost in overall performance also makes the a6400 the snappiest a6x00-series camera yet, but not as snappy as competitors.

Key takeaways:

  • Real-time Tracking AF makes the a6400 an excellent family or casual sports camera
  • The myriad AF modes and settings are confusing, and some are unnecessary
  • Good 'hit rate' whether you're shooting at 8fps with a 'live view' between shots and 11fps without live view
  • Generally snappier operation than previous a6x00 cameras, but still a laggy experience in comparison to rivals

In depth

As with all of Sony's recent cameras with on-sensor phase detection, the a6400 is, frankly, spectacular at autofocus. Whether you're shooting moving subjects at a distance or social snaps close-up, the a6400's Real-time Tracking AF is incredibly reliable and sticks to subjects with remarkable tenacity. This sort of autofocus capability was, until recently, really reserved for high-end and specialized sports cameras, so it's really encouraging to see Sony bringing this capability down-market. But it's not all perfect.

So. Many. Options.

That image above shows the full list of AF area modes on the a6400. By default, they're all enabled, and I'll admit it's nice to see that you can select which you want access to and which you don't. But why are there so many in the first place? The 'Center' AF area is exactly the same as any of the 'Flexible Spot' modes, when that flexible spot is in the center of the frame.

Then there's the dubious utility of duplicating every area mode for tracking, including having a separate option for each size of Flexible Spot - why not just have one 'Flexible Spot' mode, with the provision to change the size, like on Panasonic or Fujifilm cameras? That alone would cut down on a lot of this clutter.

The good news is, once you set the AF system up, you almost never have to touch it again

Also, using 'Wide' and 'Wide: Tracking' in AF-C results in almost the exact same experience at first glance, and I bet it's going to confuse people.

So, the system can be complex and confusing. But the good news is, once you set it up, you almost never have to touch it again: here's how we've taken to using our a6400 for all kinds of shooting, including our AF tests.

Setting up the AF system

I used this setting for 99% of my time shooting with the a6400.

Our preferred way of working goes like this: We generally keep AF-C enabled, enable face and eye detection in the menus, then select the Tracking: Flexible Spot M focus area. With this setup, you can move the Flexible Spot around using the touchscreen, and once you half-press, the camera will begin tracking whatever is underneath it. If it's a person, the camera will automatically transition to face and eye detection. If it's another object, it will track that object; even if there's a person in the scene.

That last part is crucial: many other autofocus systems, including those from Olympus and Fujifilm for example, won't let you focus on non-human objects if they detect a human with face and eye AF enabled. Those settings override everything else, and so you'll find yourself diving into menus or assigning custom buttons to enable and disable face and eye detect. With the a6400, you can leave those on all the time, but still choose when to use them depending on where you place your Flexible Spot.

One niche situation where you may run into problems would be photographs where you want a person's face in the background, blurred, with a main subject in the foreground in focus, like a staged 'ring' portrait for an engagement:

This image was not shot on the a6400 and is shown for illustrative purposes only. Photo by Carey Rose

One drawback of Sony's system is that if you try to initiate tracking on a subject that is close to a person's face, the tracking box will often jump to that face and begin Eye AF. In this instance, the ring is likely far enough away from the people's faces to avoid that in this image, but this is a specific situation you may want to be careful in.

Now, let's take a look at how the system performs.

AF system 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.

All images captured using the Sony 70-200mm F2.8 GM.

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 Real-time Tracking mode, so it needs to identify and follow a subject around the scene, as well as trying to keep it in focus.

Both of these rollovers show the results using the maximum burst speed of 11 fps, but you can expect similar results if you slow down to 8 fps to get a live feed between shots. As you can see, the a6400 turns in as near-as-makes-no-difference 100% success rate, which was repeatable over several runs. That's some solid performance, especially for a camera at this price point.

Eye detection with Real-time Tracking

Eye AF helped me nail focus in this image, easily grabbing onto the model's eye in the reflection. Out-of-camera JPEG.
Sony 24mm F1.8 Zeiss | ISO 640 | 1/250 sec | F1.8

With the acknowledgment that we may be laboring the point here, Sony's Real-time Tracking AF that basically 'includes' Eye AF is among the best autofocus implementations we've ever seen, and is capable of truly impressive results. As stated earlier on the page, you can essentially set the camera up in this way and forget it, since it works well on most everyday subjects. The only caveat is if you're using a slower zoom lens with very low light levels, where you may want to switch into Single Autofocus and deal with a bit of a slower acquisition time in exchange for consistently accurate focus. Thankfully this is easy to do by simply assigning a custom button to activate any AF area mode in AF-S using the 'Recall Custom Hold' button customization.

Overall camera performance and silent shutter

Sony's cameras, while some of the most technically capable on the market, still lag behind the competition in one key area: overall responsiveness (this is despite having an incredibly responsive autofocus system, for example). What we mean by this is that, from boot-up times to menu navigation to simply adjusting your exposure parameters, you can expect a 'hiccup' from the time of your input to the time the camera responds to it.

The a6400 still lags behind the competition in overall responsiveness

That said, the newer processor in the a6400 seems to have helped here somewhat. Boot-up times are noticeably faster on the a6400 than the older (but higher-end) a6500, but you still may find the camera changing exposure settings either too slowly, relative to how many clicks you've moved the command dial. One thing that helps this greatly is disabling 'Exposure Set. Guide' in the 'Display/Auto Review 1' menu (camera tab 2, page 6), which disables some animations that would otherwise occur when you twiddle a dial.

As far as silent shutter, the a6400's sensor is identical to that in the older a6300, which was known for having some silent shutter artifacts due to a slow-ish readout speed. For reference, the read-out speed is around 46ms (1/22 sec), whereas Olympus' E-M1X is 16ms (1/62 sec).

Rolling shutter artifacts can appear as slanted verticals if you are panning the camera while shooting, and you may also find banding under some types of artificial light or distortion of fast-moving subjects. It's far from a deal breaker, and for occasional use in crucial situations (sleeping newborn photography, or photography in sensitive spaces), it generally works well. Unlike most of its rivals, the fully electronic shutter can't be used to extend the camera's shutter speed range, so you're always limited to 1/4000th of a second, which may feel restrictive if you're trying to use wide-aperture lenses outdoors. An improvement on the a6400 is the ability to use silent shutter at fast continuous burst rates.