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Key takeaways:
- BSI CMOS sensor with phase-detection elements
- Updated processor improves responsiveness and enables high bitrate video
- UHD 4K from full-width at up to 60p, native UHD from 1.1x crop at up to 120p
- H.265-based XAVC HS and All-I H.264 XAVC S-I options
- 60p recording for 'at least an hour' at room temperature
Sony says the a7S III was developed with reliability as a foremost concern. So, rather than trying to shoot 8K or even oversampled 4K, it shoots essentially 'native' 4K. This is likely to result in slightly less detailed footage than some of the company's existing, less video-focused models, but with the benefit of improved rolling shutter and extended record times.
As with the previous a7S models, Sony talks about the camera being a good stills option for low light, but the bulk of the advances in the camera are on the video side of the ledger.
Sensor and processor
While the 12MP resolution hasn't changed, the a7S III has a different sensor to the one used in its two predecessors. It moves to a BSI design, which Sony says will boost its low light performance (though in the examples we've previously seen, it's a change that makes less and less difference, the larger the pixels are). Interestingly, it features a base ISO of 80, which could bring greater dynamic range.
What's definitely improved is the sensor readout rate. The a7S III can shoot UHD 4K at up to 60p from its full width (4.2K) or at 120p from a native UHD 4K region (a 1.1x crop).
As well as an updated sensor, the a7S III is the first Alpha camera to feature the new Bionz XR processor. It's a two-chip processing system that Sony says allows image and video processing to be handled entirely separately from file management and handling, which should reduce latency and allow more complex image processing above and beyond what the claimed 8X increase in processing power brings.
Updated autofocus
Unlike previous 'S' models, the a7S III includes on-sensor phase detection elements, allowing more decisive, depth-aware focusing. The camera includes the latest version of Sony's autofocus system, which can automatically detect faces, eyes and heads, and use the appropriate focus method. This lets you use face detection AF, including in video recording, without the risk of the camera refocusing to a different person if your original subject turns away.
Sony says the new processing improves the performance of the recognition aspect of the AF system.
Not all of the video AF system is quite as sophisticated as in stills: you have to tap to initiate tracking, rather than being able to pre-position an AF point, and there's no animal eye AF in video mode. But it should be a huge leap forward compared to the contrast-detection of the previous a7S cameras. As you'd expect, video mode lets you specify the speed of AF and how long it waits before switching subjects.
White balance sensor
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It's been a long time since we've seen a dedicated external white balance sensor on a camera (Range-topping DSLRs from Canon, Nikon and Olympus used to have them), but they've become common on smartphones. And now there's one on the front of the a7S III.
Combined with the option to control how quickly white balance reacts to changes in the scene (Exposure/Color|White Balance|Shockless WB), it's aimed at reducing unpredictable white balance shifts as you're capturing video (if one color suddenly fills the frame, for instance).
Video compression options
Perhaps the most significant improvement for most videographers is the more extensive range of compression options. The a7S III goes far beyond the 8-bit capture of previous a7 cameras. Not only does the camera gain a 10-bit 4:2:2 version of the (H.264-based) XAVC S encoding, it also gains an H.265-based variant called XAVC HS. There's also an H.264 All-I option called XAVC S-I.
UHD 4K options
Most of the camera's UHD footage (at least up to 60p) is taken from essentially the full 4240 pixel width of the sensor. This is sufficient that Sony could provide DCI 4K (4096 x 2160) options, but such options are not present.
| Frame rates | Bit-depth/ chroma | Chroma sub-sampling | Bitrate (Mbps) |
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| XAVC HS (H.265) |
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10-bit | 4:2:2 |
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| 4:2:0 |
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4:2:2 |
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| 4:2:0 |
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4:2:2 |
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| 4:2:0 |
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| XAVC S (H.264) |
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10-bit | 4:2:2 |
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| 8-bit | 4:2:0 |
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10-bit | 4:2:2 |
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| 8-bit | 4:2:0 |
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10-bit | 4:2:2 |
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| 8-bit | 4:2:0 |
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| XAVC S-I (All-I H.264) |
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10-bit | 4:2:2 |
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Boxes marked in green require at least a V60-rated SD card. Boxes marked in red require a V90. Bit-rates around 100Mbps require a V30 card. CFexpress cards can record all modes.
One thing that's interesting about the a7S III's XAVC HS implementation is that it captures the same bitrate as the conventional XAVC S footage. The H.265 codec is more efficient than the older H.264 system, so the XAVC HS files should be able to retain more detail about the scene and movement within the scene in the same file size.
Meanwhile, there's also an All-I variant of XAVC S. This is still based around H.264, but treats every frame as an 'Intra' frame: saving full information about it, rather than saving the differential information about what's changed between more occasional 'I' frames. This is mainly valuable for encoding complex motion and detail in busy scenes.
It's actually possible to capture All-I footage at 4K/120p but this can only be done without audio, via the S&Q slow-mo mode, which keeps the write-rate down to 240Mbps.
1080 video options
As with the original a7S camera, the Mark III's 12MP can either be seen as a (give-or-take) native 4K sensor or as a sensor that provides perfect 2:1 oversampled 1080 footage. The same codecs and bitrates are available from a Super 35 crop. The cropped version isn't oversampled.
| Frame rates | Bit-depth/ chroma | Chroma sub-sampling | Bitrate (Mbps) |
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| XAVC S (H.264) |
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8-bit | 4:2:0 |
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10-bit | 4:2:2 |
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| 8-bit | 4:2:0 |
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10-bit | 4:2:2 |
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| 8-bit | 4:2:0 |
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10-bit | 4:2:2 |
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| 8-bit | 4:2:0 |
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| XAVC S-I (All-I H.264) |
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10-bit | 4:2:2 |
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120p/100Mbps requires at least a V30-rated SD card. Boxes marked red require at least a V90 SD card. CFexpress cards can record all modes.
It's worth noting that there's no H.265 option for 1080 capture. Also note that All-I recording demands a CFexpress card or V90-rated SD card even for 89Mbps 24p capture, presumably because the camera needs to be certain it can clear its buffer.
Raw video output
As is the case on many recent cameras, the a7S II can output a Raw video stream for external recorders to then encode. Unlike most of its rivals, the Sony promises to output 16-bit data from its sensor.
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| The camera has an HDMI v2.1 port allowing the fast data transfer to allow 16-bit Raw output. |
Bit depth of Raw isn't directly comparable to bit-depth of gamma-encoded data and doesn't improve quality once you have sufficient data values to capture all the sensor's dynamic range, so most cameras won't show any benefit to offering more than 14-bit Raw.
However, with its large pixels, the a7S III could be the first camera we've seen where the the camera is capturing so much DR at a pixel level that it needs 16 bits to fully encode all that tonal range. This will be an interesting thing to explore once an external recorder offers support for the camera.
There's no 16-bit mode for stills shooting.
Separable stills/video options
New to the a7S III is the ability to control which settings do and don't carry across between stills and video. If you're just grabbing quick clips it can be handy for settings like white balance to carry over from stills to video but if you're trying to capture both types of media to a high standard, it's common to require different settings. Separating the settings then lets you jump back and forth between stills and video shooting, without accidentally shooting Log stills or capturing video clips with 1/500 sec shutter speeds.
The menu option 'Setup|Operation Customize|Different Set for Still/Mv' lets you choose which of the following settings maintain different stills and video values:
| Camera parameters that can be set to hold different values for stills and video modes |
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HEIF stills capture
As well as JPEGs, the a7S III can also capture 10-bit compressed files using the HEIF format. This gives the option of 4:2:0 or 4:2:2 color subsampling. We'd recommend taking the 10% increase in file size to retain more color resolution (4:2:0 is something you usually only encounter in highly compressed JPEGs, in the stills world).
Interestingly, unlike Canon, the Sony doesn't assume you're using the move to 10-bit to record lifelike HDR images and will just use whichever color mode you were using for JPEGs. So, while there's the option to shoot HDRTV-ready images using several variants of the Hybrid Log Gamma tone response (and these will work best in HEIF) you can also shoot 10-bit images with the Standard 'Creative Look' or if you wish. Or even S-Log for that matter.
Neither the EVF nor LCD is able to show HDR images but there is a choice of Gamma Assist modes to give you a more usable preview. You need to manually select the appropriate assist mode to match your current shooting mode.
Quad-channel audio
The a7S III has the ability to record up to four channel audio in its video, rather than just two. To do this it needs to be used with the XLR-K3M adapter. This features two XLR inputs and a 3.5mm stereo input (though the left and right channel of the 3.5mm input can't be adjusted independently).
There's an option in the Setup menu to select which inputs are output to the two monitoring channels. This includes the option to hear channels 1 and 3 in one ear and 2 and 4 in the other, for full four-channel monitoring.
How it compares:
The Sony a7S III may look a lot like other mirrorless full frame cameras (including being near-identical to the a7R IV), but its focus on delivering high-end video makes it most directly comparable to Panasonic's Lumix DC-S1H.
We've included Sony's a7 III here to show what you gain over a more mainstream camera and have included Canon's EOS R5 for similar reasons: both these cameras are primarily aimed at stills shooters but appear to have strong video specs on paper.
| Sony a7S III | Panasonic Lumix DC-S1H | Sony a7 III | Canon EOS R5 | |
|---|---|---|---|---|
| $3500 | $4000 | $2000 | $3900 | |
| Resolution | 12MP | 24MP | 24MP | 45MP |
| Sensor type | BSI CMOS | BSI CMOS | BSI CMOS | Dual Pixel (FSI) CMOS |
| Autofocus type | Phase detect | DFD (Contrast-based) | Phase detect | Dual Pixel (Phase detect) |
| Image stabilization | Up to 5.5EV | Up to 6.5EV | Up to 5.5EV | Up to 8EV |
| Burst shooting rate | 10 fps | 6.0fps with AF-C | 10 fps | 20 fps (e-shutter) 12 fps (mech) |
| Viewfinder | 9.44m dots 0.90x mag |
5.76M dots 0.78x mag |
2.36M dots 0.76x mag |
5.76M dots 0.76x mag |
| Rear screen | 1.44M dots Fully-articulating |
2.3M dots Tilt + Articulating |
0.92M-dot Tilting |
2.1M dots Full articulating |
| Full-frame video options (Capture res and max frame rate) |
UHD full-width (4.2K 60p) UHD 1.1x crop (4K 120p) |
DCI/UHD Full Width (5.9K 30p) |
UHD full-width (6K 24p) UHD 1.2x crop (5K 30p) |
DCI/UHD 8K full width (8.2K/7.7K 30p) DCI/UHD 4K full width (8.2K/7.7K 30p) DCI/UHD full width (?/? 120p) |
| Super 35 video options (Capture res and max frame rate) |
Full HD (1080 120p) |
DCI/UHD (4K 60p) |
UHD (4K 30p) |
DCI/UHD 4K (5.1K/4.8K 60p) |
| Raw video | External 4K/60 16-bit |
External 6K/24 12-bit (promised) |
No | Internal 8K/30 12-bit (20 min) |
| Log modes | S-Log2 S-Log3 |
V-Log | S-Log2 S-Log3 |
C-Log |
| HDRTV modes | HLG | HLG | No | PQ |
| Highest quality codec | 10-bit 4:2:2 H.265 XAVC HS | 10-bit 4:2:2 H.265 | 8-bit 4:2:0 H.264 |
10-bit 4:2:2 H.264 |
| All-I option | 10-bit 4:2:2 H.264 XAVC S-I | 10-bit 4:2:2 H.264 | N/A | 10-bit 4:2:2 H.264 |
| Time limit | >1 hour 4K/60p | Unlimited | 29:59 with thermal warning disabled | 29:59 or thermal limit |
| Shooting aids |
Peaking |
Peaking Zebras Waveforms Vectorscope |
Peaking Zebras PDAF |
Peaking Zebras Dual Pixel AF |
| Media formats | Dual UHS-II / CFexpress A | Dual UHS-II | 1x UHS-II 1x UHS-I |
1x CFexpress B 1x UHS-II |
| Other notes | Up to 4 channel (with XLR adapter) | Dual audio gain levels TC sync |
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| Battery life LCD / EVF |
600/510 | 400/380 | 610/710 |
490/320 |
| Weight | 699g | 1164g | 650g | 738g |
| Dimension | 129 x 97 x 81 mm | 151 x 114 x 110 mm | 127 x 96 x 74 mm | 139 x 98 x 88 mm |
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