Sony A6400 Real Time Tracking autofocus

Sony A6400 Autofocus: Real Time Tracking

The introduction of the Sony A6400 (See on Amazon / Adorama) brought the promise of a major autofocus innovation: real time tracking. All modern interchangeable lens cameras have the ability to autofocus continuously, adjusting the depth of the focus as the subject moves to and from the camera. In most cameras, this requires you to keep an autofocus point over the subject. Some cameras also have the ability to track focus laterally (subject tracking): a focus point can follow the subject as they move side to side, and as they move to and from the camera. Nikon’s version is called 3D tracking and it works pretty well. Up to now, Sony had a feature called “Lock-on AF.” 

In many ways, the real time tracking of the Sony A6400 isn’t new but simply an improvement on Lock-on AF. In my own use shooting multiple recent Sony cameras, lock-on AF was extremely unreliable. You could pick a subject to track focus on, but focus points would routinely jump on and off the subject, often jumping to a different subject entirely.  Additionally, while it might track a person for example, it didn’t track the face or eye specifically. 

The advancement of “real time tracking” is that the focus point is supposedly much stickier — it should stick to your subject. The even bigger factor is that “artificial intelligence” is used to give the camera a better understanding of the subject. So if you lock focus on a person, even starting on their chest, the camera will recognize that it’s a person and will attempt to continuously track their face and their eye. 

It’s interesting that Sony first launched this major feature upgrade not on one of their premium models, but on an intermediate consumer model, the Sony A6400. With more camera makers focusing their serious users on full frame models, the Sony A6400 is clearly intended for more intermediate users who want a lot of features packed into a small body at a reasonable price. (See the Sony A6400 on Amazon / Adorama) . In the very near future (maybe by the time you read this), the feature is supposed to be introduced to the Sony A9 by a firmware update. There are no known plans to bring the feature to other models with firmware updates, but you can be certain it will be found in new models going forward.

So does it work?!?!  

Testing Sony A6400 Real Time Tracking

With the help of my kids, I tested the Sony A6400 tracking in a few scenarios that should simulate real world use. I essentially had my kids walk towards the camera in a bit of a zigzag. They didn’t walk slowly, but they also didn’t run around erratically. I recorded through the viewfinder, so you can see exactly what I saw. 

For this first set of tests, I used the Sony A6400 with Sony 18-135mm lens (See on Amazon / Adorama).  I suspect this will be a popular kit lens for A6400 users. I’ll be reviewing it in the near future — it’s definitely a kit lens but a pretty good one. I kept my shutter speed up, so that motion blur wouldn’t be an issue in the test. As the lens is not a fast aperture lens, the ISO had to be pushed up in some of these images.

Real Time Tracking: Single Shot

In this first test below, I tracked my daughter as she walked towards me, and the camera was set for single shot mode. I took a handful of shots as she approached, re-locking the focus after each shot. As you can see in the video, the camera did an excellent job of acquiring and keeping her eye.

Just because the green dot was in the right place, it doesn’t mean that the final image was actually in focus. So here are some close crops of the face in the images that were taken:

In single shot mode, the results are impressive. I could half-press the shutter button, it kept focus on the eye, and I got a nicely focused shot when I chose to fully press the shutter. Not sure I would say the focus was perfect in every shot but it was pretty close.

Real Time Tracking and Burst Shooting

The Sony A6400 is capable of shooting at a pretty high frame rate, up to 11 frames per second. But I do not recommend ever using this 11 fps setting (called Hi+ in the drive menu).  The Hi+ setting does not give the photographer a real time view through the viewfinder. If you want a real time view, stick to the “Hi” setting which still gives a rather speedy 8 frames per second. 

This next video includes two tests, shooting with real time tracking at 8 frames per second. I start in focus mode “Tracking: Flexible Spot S(small).” This mode allows me to identify the subject at the start and then let the camera tracking take over. These are rather long bursts with 50-60 frames in each burst of about 7 to 8 seconds.

Looking at the video, the results are a bit of a mixed bag. First, I’ll note that shutter blackout is pretty minimal and you do get  pretty good real time view at 8 frames per second.  It’s a very “dslr-like” shooting experience and that’s a positive thing.

The “green dot” couldn’t really keep up and jumped around a lot, but it did not entirely completely jump off the subject and get lost – it always returned to the subject. It just felt like the green dot was always lagging behind where the eye had been. Of course, it’s possible that the green dot was off but the focus was actually on.

So let’s look at some close crops:

In the first sequence of my daughter, in 61 images, focus was badly missed in 5 images. These are the 3 of those misses:

With 5 total misses, that still left 56 out of 61 images with “acceptable” focus. A 92% hit rate for a consumer camera shooting a 7 second burst is actually really really good. I would not expect most older Sony cameras to maintain a zigzagging subject for 7 seconds. 

Unfortunately, while focus was “acceptable” in 56 out of 61 images, focus was not perfect. The kit lens has slow aperture and therefore pretty wide depth of field. When looking carefully, it’s obvious that for many of the captures, the subject was within the depth of field but focus was not perfectly placed on the eye. In pixel peeping this first test, I found about half had acceptable but imperfect focus. (5 images were totally missed focus, another 25 were “close.”) To give you an idea of what I mean by close but imperfect, these are some of the crops:

Each of the above images look acceptable when viewed at normal size, but cropping close to the face reveals they really just aren’t perfect. As shown in the video above, I repeated the test with my son and got similar results. In the second test, focus wasn’t really completely missed in any shot, at least not as badly as in the first test. Of 51 shots, about 27 were slightly off, and I deemed 24 to be pretty close to perfect focus. Of the 27 that were off, some were more off than others. A sample gallery of some of the images that were off:

If the above photos were not cropped and were displayed on facebook, they wouldn’t look too bad. But close examination reveals focus was definitely missed, you wouldn’t want to make large prints of these images. In the first image above, there is some pretty bad back focus.

Let’s take a look at some of the images that really did get focus. Note that ISO got high in some images, so they may get noisy.

Before we get into conclusions, one more test:

Real Time Tracking Burst with Sony 85mm F/1.8 lens

I decided to repeat the test with a fast aperture lens, the Sony 85mm F/1.8, shooting at F1.8 aperture. (Review of the Sony 85mm F/1.8 / See on Amazon / Adorama ). The much faster aperture brings some major consequences:

• Narrow Depth of Field will make “misses” more more blatant
• Wide aperture will give the autofocus system more light to function
• Narrow Depth of Field could potentially make it easier for the autofocus system to discriminate proper autofocus

The EVF video:

To my eye, the video looks slightly better than the kit lens. The focus box still jumps around, still jumps between focus on the eye and focus on the face, but overall the focus box seems a bit stickier to the face and eye region.

This slight improvement also shows up in the crops. Of 61 captures in 7.5 seconds, there were no horrible misses. Focus was at least pretty close in 100% of the shots. I’d say 32 were pretty close to perfect, with the other 29 pretty acceptable.

Some of the “acceptable crops”:

Side by side, here are a couple of the final frames, 1 with perfect focus and 1 just barely off:

And here are a few more frames where the real time tracking nailed for focus:

You can see, that overall, the misses with the 85/1.8 weren’t too bad at all. The real time tracking delivered fairly nice results with the faster lens. Still not perfect, but very good for a consumer camera.

Cautious Optimism for Real Time Tracking on the Sony A9

The Sony A9 firmware update is imminent promising the same feature, though I expect the feature to be far better on the A9. (See the Sony A9 on Amazon / Adorama). Costing more than four times as much, the Sony A9 has some critical advantages over the A6400. The above test was taken with a mechanical shutter, closing 8 times per second. When the shutter closes, the AF system is momentarily blacked out. The Sony A9 shoots 20 frame per second bursts with an electronic shutter, so the AF system is never blacked out. This should theoretically offer a critical advantage in continuous tracking. (While the Sony A6400 offers an electronic shutter option, rolling shutter prevents it from being suitable for photographing moving subjects). Secondly, the stacked sensor and processor in the Sony A9 are just faster than the Sony A6400. Sony brags that the Sony A9 can calculate autofocus 60 times per second, but they don’t make such claim for the A6400. So with the ability to perform 60 autofocus calculations per second plus the electronic shutter, I’m cautiously optimistic that the real time tracking will be fantastic on the Sony A9.

Real Time Tracking AF Conclusions:

If you’re an intermediate-consumer type of photographer, you will probably appreciate the real time tracking autofocus on the Sony A6400. It will help you get a greater total number of “keepers” than you would get on other similarly priced cameras. For “people” shooters, it’s a good reason to buy a Sony A6400. (I recommend the Sony A6400 with the 18-135mm lens). 

If you are a professional or very advanced user, the Sony A6400 real time tracking option may not be reliable enough to get you truly critical autofocus. Of note, it’s better with a fast lens shooting at wide aperture. In such cases, it may be pretty darn good, probably one of the best subject tracking systems around. But few professional photographers find any subject tracking system to be reliable enough, instead relying on depth tracking modes.

This might change with the Sony A9. You can expect me to run further tests with the A9 after the firmware update. If it improves upon the real time tracking in the A6400, then A9 users are in for a very special firmware update.