Autofocus Overview

Relative to its predecessor, the Sony a7 III gets an all-new autofocus system that is among the most capable in mirrorless cameras today. We know autofocus can be a complex issue, so we've broken down the key takeaways of what you need to know about the Sony a7 III's autofocus system. You'll find more detail further down this page.

Key takeaways:

  • There are a total of 693 phase detection autofocus points that cover almost all of the frame - that's tied for the most we've seen on any camera, ever
  • Using the camera in Continuous autofocus (AF-C) will give you the fastest performance most of the time (see stop-down focusing below).
  • We like the 'Wide' autofocus area for general shooting, 'Flexible Spot' for choosing a more specific area with the joystick, Eye AF for portraits and Lock-On AF - Flexible Spot for letting the camera track a moving subject
  • We've found the a7 III to be more reliable than the a7R III in Lock On AF mode
  • If you're shooting video, the 'Wide' autofocus area does a good job of focusing for you, since choosing your subject using Sony's 'tap-to-track' implementation isn't as user-friendly as the competition

Now that we've covered the basics, let's take a closer look.


In-depth

The Sony a7 III inherits what is basically the same autofocus system as the $4500 professional a9. Those 693 phase detection autofocus points are spread over 93% of the frame. That's a lot of numbers, but what it equates to is this:

Each of those dots represents an autofocus point, with only the very left and ride sides of the frame left uncovered.

There are also 425 zones of contrast-detection autofocus, and Sony claims that both the a7 III's autofocus speed and tracking performance are twice as fast as the a7 II. Low light autofocus is claimed to work down to -3 EV with an F2 lens, which is about the brightness of a full-moonlit night. Our own testing confirms this, and the camera in single autofocus mode holds up well against the Nikon D5, which continues to be one of our autofocus benchmarks.

The a7 III also gains the ability to switch autofocus areas depending on whether the camera is in the horizontal or vertical orientation, and you can adjust the tracking sensitivity depending on how quickly you want the camera to refocus on a moving subject, or a subject that is obscured by other subjects or objects.

AF Area Modes and Lock On improvements

As with the a7R III and a9, the a7 III offers the following autofocus area modes.

  • Wide*
  • Zone
  • Center*
  • Flexible Spot (Large, Medium, Small)*
  • Expanded Flexible Spot
  • Lock On Area modes (Tracking versions of each of the above modes)

* indicates AF modes available with adapted lenses in AF-C at up to 3 frames per second.

As the descriptions imply, these modes generally contract in size from 'Wide' area, that chooses a subject that's close and central, through to a specified spot. The Lock-On versions of each mode, available only with AF-C, try to recognize and track whatever's in the AF area when you half-press the shutter.

Key to autofocus performance on the a7 III is the way it behaves in Lock On when tracking subjects. Sony's included the same motion prediction algorithms as the a9, and once you initiate tracking on a subject, a cloud of autofocus boxes appears over your subject and will stick to it tenaciously as it moves about the frame.

This behavior is different to the a7R III, which uses older algorithms to draw a large box around what the camera believes is your subject; we've found that the a7 III and a9 both perform more reliably than the a7R III in Lock On AF mode.

Eye AF

The a7 III now includes Sony's impressive Eye AF feature. Used in Continuous Autofocus, Eye AF will reliably track the eye of your subject that's closest to the camera, ensuring a sharp shot even at F1.4.

Sony's Eye AF feature nailed focus on this child mid-swing. Edited to taste in Capture One 11.
Sony FE 85mm F1.8 | ISO 250 | 1/2000 sec | F1.8
Photo by Rishi Sanyal

If you have multiple subjects in the frame and are using any AF area other than 'Wide,' you can place that AF area over one of the subjects, and if you initiate Eye AF, it will track the eye of that specific subject; to change subjects, release the Eye AF button, place your AF area over the other subject, and re-initiate.

The a7 III will continue to track your subject's eye, even when firing away at 10fps, so it's a great option for catching just the right expression. Like the a9 and the a7R III, it's incredibly 'sticky' to the person you initiated on, rarely jumping off to someone else in the scene.

What's more, Eye AF is even available with adapted lenses, even in AF-C at up to 3 fps bursts.

Stop-down focusing

A caveat to all of the impressive autofocus technology in the a7 III is that this camera (as well as the a7R III) unfortunately still suffers from issues connected to 'stopped-down focusing.'

In essence, this means that when shooting with continuous autofocus, the camera will initiate and then continue to focus at the shooting aperture. If you're shooting moving subjects at smaller apertures you're potentially starving the AF system of light, and decreasing the phase separation between 'left' and 'right' (or 'up' and 'down') looking pixels, which could result in inaccurate focus. This can become particularly problematic when stopping down in low light or backlit situations, both instances where the AF system is already stressed by a drop in subject contrast.

If you're shooting moving subjects at smaller apertures, you're potentially starving the AF system of light

One way around is to shoot AF-S, which does focus wide open for most lenses (there are exceptions), but that's not suitable for moving subjects. AF-S is also slower than AF-C (shooting wide open) in most instances, since it goes through an extra contrast-detect confirmation step.

There's really no way around this at this time, and can be particularly frustrating for those wishing to have some extra depth of field - or a sunburst or two - in lower light or backlit situations. We'll look in more detail at the potential impact of this on the next page.