There are a lot of capable premium 1" sensor bridge cameras on the market. But as this class of camera has matured, one aspect that's remained unchanged is the use of Contrast Detect AF systems only. CDAF, while reliable and precise in decent light, is prone to hunting in low light and/or toward the tele-end of some cameras' zoom ranges.

Enter the RX10 IV: it uses a hybrid phase and contrast detect AF system. The sensor has 315 phase-detect points built-in covering 65% of the total surface area.

Phase detect AF points (green) cover 65% of the total RX10 IV's sensor area.

It's the same sensor and AF system used in the RX100 V, which proved extremely capable at tracking even at its top speed of 24 fps. But the RX10 IV has a lot more lens to move than its pocketable sibling. So just how good is AF on the RX10 IV?

Continuous AF

Truly, 24 fps is a crazy fast burst rate – in our field testing we found the 10 fps burst rate using 'continuous shooting Mid,' to be more than enough speed for most subjects. But there are plenty of use-cases when a 24 fps burst rate with AF might be super useful.

In our first test, we had our subject approach the camera in a straight line, while we held a single point over them and fired at the top speed. This lets us see if the camera can drive the lens fast enough to keep the subject in focus as they get closer and closer.

1 2 3 4 5 6 7 8 9 10

The results of this test are indeed impressive: the RX10 IV's hit rate using a single point to maintain focus at 24 fps is close to perfect – cool.

Subject Tracking

Our next demo is a bit more complex: it tests the camera's ability to recognize and follow a subject moving toward the camera in an irregular pattern and is meant to simulate situations like a child running around on a lawn. We set the camera to its 'Lock-on AF: Flexible spot M' focus area for this test and placed the initial point over the subject at the start of their weave.

The results of this test are also highly-encouraging: the camera's hit rate is once again nearly perfect when it comes to tracking a subject moving irregularly at 24 fps. Sweet!

Limitations for sports and action

So at this point you're probably pretty impressed with what the RX10 IV is capable of, from an autofocus perspective, which you should be! But all this speed and AF ability comes with some caveats, the biggest being: you can't hold focus while also zooming the camera.

Any serious sports photographer knows that the ability to zoom out on a subject as they approach, while also maintaining focus is essential to the way most people shoot action. We've reached out to Sony to see if this is something that could perhaps be enabled via firmware update.

That's not all though. Other real world limitations include a buffer that can be slow to clear, locking you out of shooting in peak moments. This is true especially when using the camera at its top burst rate, even with a fast card. Finally, there's no ability to tell the camera what to do if it suddenly encounters a closer subject, something most sports cameras let you fine tune from within the menus.

Close-range AF and casual shooting

Sony's high-end cameras offer a ton of different AF settings, some of which are confusing and/or repetitive. That said, the default 'Wide' focus area is excellent for casual shooting or when shooting toward the wide end of the zoom range – by default it prioritizes locking focus on a face if one is found in the scene. If you are shooting in AF-C, it will track whatever it initially locks focus on which is very handy.

Eye AF works great, even on 4 legged friends. Out-of-camera-JPEG. Photo by Dan Bracaglia.
ISO 1250 | 1/500 sec | F4 | 214mm

We also recommend customizing a button to 'Eye AF.' This feature, when enabled is truly impressive at finding an eye of face in a scene and locking focus.

Video AF

The good news is it is simple to place a point over a subject in video mode and the camera does a great job maintaining focus in AF-C with almost no hunting. The new touchscreen also makes racking focus incredibly simple - just tap the screen to jump between focus points. You can even adjust the video focus speed (slow, normal, fast). You can see an example of that in the video above.

The bad news is you can not use tracking or Face Detect when 1080/120p video, or when capturing Proxy files alongside your 4K footage. 'Wide' AF area + AF-C can be used to track subjects in video mode, but the camera determines what it focuses on. In general, the RX10 IV will lock onto whatever is closest or most central in the frame, but it will not display green AF boxes to confirm the point/area of focus - frustrating!

When shooting 4K video without proxy files, or 1080 at 60p or below, Face Detect is available as is subject tracking, via the 'Center Lock-On AF' option in the Menu. Users are greyed out of all the 'Lock-on' options available in the AF area mode menu when shooting video.