Autofocus overview

Out of camera JPEG.
Sony FE 24-105mm F4 G @ 91mm | ISO 100 | 1/250 sec | F5
Photo by Carey Rose

Sony's a7R III comes with some impressive autofocus specifications, including 399 on-sensor phase detection AF points, and a wide array of options concerning how you'd like to utilize them. At the base of all of these are the AF drive modes, AF-S, AF-C and AF-A (for 'Automatic'), which chooses between the other two drive modes, based on its understanding of the subject.

There are menu options for AF-S and AF-C to dictate whether the camera should prioritize achieving focus, maintaining continuous drive speed or striking a balance between the two when you're shooting bursts of images.

Beyond this are the camera's AF area modes, which define what the camera tries to focus on.

AF 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]

As the names imply, these 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.

This diagram represents the AF array of the older a7R II - the a7R III has the same number of phase detect points as you see here, but increases the 25 contrast detect areas here to 425.

On top of all these area modes are three additional AF functions that build-on or override your choice of AF area mode:

  • Face Priority in AF*
  • Eye AF
  • Center Lock-On AF

Face Priority will focus on a face, if your chosen AF area or region is near it. Eye AF will totally override the chosen region and focus on the nearest eye it can find, though if your underlying option is a Flexible Spot, you can place that spot over your chosen subject's face to tell Eye AF to initiate on that person. In S-AF mode, Face Priority focuses on the subject's eye, without the need to hold the 'Eye AF' button down.

The Center Lock-On AF function will switch the camera to Wide area mode and track until you dismiss it, at which point it'll revert to your previously chosen AF area.

*Note that Face Priority's effect on metering is now a separately controlled option

Behavior

Wide area mode with C-AF will continue to focus on the subject it initially finds, if it or the camera moves. However, this is distinct from the behavior of Lock-On Wide Area and AF-C. The distinction is that the Lock-On mode will attempt to recognize the subject. The difference becomes clear if something temporarily blocks the shot: Wide area will refocus on whatever is close/central, whereas Lock-On Wide will try to find the original subject, wherever it is.

Eye AF

When Sony released Eye AF with the a7R II, we were pretty blown away - but they've been steadily improving it with each new camera since. For the serious portrait photographer, it's fantastic, letting you focus more on posing and expression, and leaving the focus up to the camera. Check out this demo from the a7R III launch event in New York.

It wasn't without its faults, though - burst shooting with Eye AF on the a7R II left much to be desired, with the camera struggling to accurately track the subject's eye. The a7R III fixes that - offering incredibly sticky tracking, even when shooting at the max 10fps burst speed. Despite the degree to which the camera was swung around to shoot the above video, a high number of the shots were good enough that we've included a couple in the samples gallery. We should also emphasize that Eye AF is similarly 'sticky' with adapted lenses, albeit with a maximum shooting speed of 3fps.