Video overview

The a7R III is a very well-equipped video camera, able to shoot UHD 4K video either from the full width of its sensor or from a Super 35 (essentially APS-C sized) region of its sensor. The 'full frame' 4K is pixel binned, taking groups of pixels and combining them. The Super 35 footage is oversampled (it captures 5K footage, then downsizes it), which means better detail capture: ideal if you're shooting with dedicated Cine lenses that cover the Super 35 format.

The camera can also shoot 1080p video at up to 120p and has a function to conform this footage back down to 24 or 30p, if you want out-of-camera slow-mo. These functions are also available from both the full width of the sensor or from the cropped region.

5-axis image stabilization ('Steadyshot') is available in all modes.

The camera continues to support the older AVCHD specification but all its highest-quality output is shot in the XAVC-S format. This means bitrates of 60 or 100Mbps for 4K footage and 1080/120p, and 50 Mbps maximum for 1080p60, 30 or 24. All internally captured footage is 8-bit 4:2:0, with the option to output an 8-bit 4:2:2 stream to an external recorder over HDMI.

Log capture and dynamic range

Unlike the a9, the a7R III continues to offer Sony's 'Picture Profile' gamma and gamut options cribbed from its professional video cameras. This includes the S-Log2 and S-Log3 gamma curves: very flat responses that try to squeeze as much of the camera's dynamic range into the file as possible, in a way that's recoverable.

Shooting in Log allows you to optimize exposure for the highlights of the scene without too much information clipping to black and being unrecoverable. However, given the camera's 8-bit capture, there's a risk of posterization if you have to pull your shadows and midtones up too much. This is something we'll look at in more detail at a later date.

Picture Profile is also where you'll find the camera's Hybrid Log Gamma (HLG) modes. These essentially shoot Log footage but presuppose a standard way of rendering the file and embed all the metadata to allow HLG-compatible high dynamic range displays to show the footage correctly. Sony promotes this as a means of capturing HDR footage without the need for post-processing. We'll also look into this in more detail at a future date - stay tuned.

AF in video

Autofocus behavior in video changes dramatically. Only Manual Focus and AF-C are available, while Lock On area modes are disabled. There are two movie-specific menu parameters defining the speed at which the camera refocuses and how readily it should relinquish its lock on a specific subject.

Flexible Spot and Expanded Flexible Spot modes work much as they do in stills mode: the camera will attempt to maintain focus on the specified point. If the touchscreen is enabled, the camera will move the point if you touch the screen then refocus and try to maintain focus on that point.

Wide, Zone and Center modes initially work like their stills counterparts, unless you have the touchscreen active and tap on the screen. This takes you to Spot AF mode.

Spot AF uses C-AF to refocus to the depth of whatever you've tapped on, at whatever [Movie] AF Drive Speed you've specified in the menu. It'll then drop to manual focus when it finds focus. It's a really effective way of racking focus between two subjects as you shoot. A small 'cancel' button on the screen or a press of the 'center' button re-engages C-AF.

Autofocus is pretty good at maintaining focus without excessive hunting, even when set to be responsive to changes in subject distance.

The only form of subject tracking that's available in movie mode is the Center Lock-On AF function and even then, not when shooting 4K. As in stills mode, this must be engaged from the menu, the Fn menu or assigned to a button. It switches the camera to Wide area mode then attempts to recognize and track whatever's in the center of the scene when you press the center button. Once tracking has started, you can tap elsewhere on the screen to define a new subject. As with Spot AF, an on-screen cancel button or a press of the 'center' button reverts to the underlying AF behavior.

Since it's the only way of tracking while in movie mode, it's tempting to assigning a button to engage Center Lock-On AF. We'd recommend assigning a button across both stills and video mode, so that you can easily disengage the Center Lock-On function as you swap between stills and video shooting.