SONY HAS GONE FOR SOLID SPECS and functionality with the A7S III rather than lots of bling, essentially with the objective of making it as good as is possible for 4K UHD and Full HD capture, which is still the real world for the vast majority of videographers. So, at the top of a long list of frame rates and codec options is 4K UHD internal recording at 100/120p with stereo audio and 10-bit 4:2:2 colour, giving a bit rate of 280 Mbps… and still retaining full autofocusing capabilities. Plus, the clip length limit is 20 minutes, which is longer than what most people need. There’s a small crop of 1.1x at 120fps for slow-mo effects anyway but, at 50/60p, full pixel read-out is in play
(i.e. no binning) with a clip length of one hour. Shoot 4K UHD at 25/30p and there isn’t any time limit beyond those imposed by the memory card and battery. With the Full HD resolution, you can record at up to 240fps – again with no cropping – which is obviously a
10x slow-down with a 24fps output.
The longer clip lengths are made possible because Sony has employed a passive graphite alloy heat sink shaped to optimise efficiency that's built into the image stabiliser module. There’s a balancing act here in terms of providing both effective cooling and effective weather sealing.
Three internal codecs are available – XAVC S, XAVC S-1 and XAVC HS – the latter two being new additions. XAVC S supports UHD and FHD, and employs H.264 encoding with Long GOP interframe compression to help keep file sizes small (these are output as MP4). XAVC S-1 also supports UHD and FHD, but uses the All-Intra frame-by-frame compression, so the bit rate (with 4K UHD and 10-bit 4:2:2 colour) can be up to 600 Mbps with huge file sizes. XAVC HS uses the more efficient H.265 encoding – with Long GOP compression – to keep the bit rate under 200 Mbps and create more manageable file sizes with 4K UHD. Incidentally, you can also record with 10-bit 4:2:0 colour sampling or 8-bit 4:2:0 to lower bit rates and file sizes. Handily, the A7S III has proxy recording, so a smaller file is simultaneously recorded – specifically Full HD in XAVC HS with 10-bit colour or HD in XAVC S with 8-bit colour – with higher bit-rate 4K footage that can be used for easier previewing even editing.
A 16-bit RAW video output (4K/60p) is available via HDMI (incidentally, the full-size Type A connector), and supported by the Atomos Ninja V recorder. Encoded 4K with 10-bit 4:2:2 colour and up to 50/60p is also available for external recording with, usefully, simultaneous internal capture.
There’s an improved S&Q (Slow & Quick) mode that offers a wide choice of in-camera recording frame rates and base rates to give over-cranked or under-cranked footage for slow or fast motion effects. And up to 10-bit 4:2:2 colour is available here too, with XAVC S-1 encoding giving a bit rate of 250 Mbps (so you’ll need a CFexpress card).
Both the S-Log 2 and S-Log 3 profiles are supported to make the most of the sensor’s extended dynamic range, along with four HLG (Hybrid Gamma Log) profiles (HLG and HLG1-3). The HLG profiles are designed to enable an “instant” workflow for output to compatible HDR TV displays. For straight out-of-the-camera colour and contrast variations, there is a choice of 10 videocentric Picture Profiles, and 10 Creative Look presets that have eight adjustable picture parameters.
On the audio side, the A7S III has stereo microphones with manually adjustable levels and a wind-cut filter. The camera has both a stereo audio input and output. These are both standard 3.5mm minijack connectors, but the Multi Interface Shoe, with its digital audio interface, supports higher quality sound recording (since the audio signal is transferred in digital form) with accessories such as the XLR-K3M adapter that provides two XLR balanced inputs and a 3.5mm stereo input.
In more general terms, video makers will also appreciate the upgraded AF capabilities and performance, the fully-articulating display with expanded touchscreen implementation, and the sensor’s wide dynamic range (15 stops with S-Log3) and exceptional performance at very high ISO settings. There’s also an
‘Active’ image stabilisation mode that combines electronic image shifting with the IBIS (so there’s a slight 1.1x crop). For autofocusing with video, there are dedicated ‘AF Transition Speed’ and ‘Subject Shift Sensitivity’ adjustments, and improved eye tracking is available (but for humans only). Overall, the AF response and accuracy with video is the best Sony has delivered so far, as is the reliability of the tracking and the lowlight performance. The image quality in low-light situations is exemplary, and no other hybrid mirrorless camera gets close in terms of optimising 4K functionality and performance.