Introduction
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The five-year gap between the launch of the a7S II and the announcement of the a7S III had some people wondering whether Sony had given up on the idea of a video-focused a7 model. The enhanced video capability of the core a7 line made that seem plausible (the a7 III does many of the things the a7S II did).
But the Mark III is here and it represents more than just a Mark II brought up to competitive spec. Instead it’s the most serious video camera the Sony Alpha range has ever seen and makes the older camera look rather basic, by comparison.
More frame-rate flexibility
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The biggest changes come in terms of video spec, as you might expect. The a7S II could shoot UHD 4K at up to 30p and the highest-quality setting captured 8-bit 4:2:0 footage at up to 100Mbps in the X AVCS format. It’s fair to say the a7S III goes a little beyond this.
In terms of frame rates, the a7S III can shoot 4K at up to 60p using the full width of its sensor or at up to 120p if you accept a very slight crop down to a native 3840 x 2160 region of the sensor. Its thermal management has been significantly re-worked to ensure that these capabilities don’t come at the cost of reliability: Sony says it should be able to shoot over an hour of 10-bit 4K/60 footage.
High bit depth/bitrate video
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The a7S III also gains 10-bit, 4:2:2 internal capture for the first time, which means its Log footage is much more flexible in the edit and has better color resolution than the 8-bit 4:2:0 capture of the a7S II.
There are also many additional format options on the newer camera. In addition to XAVC S footage, the a7S III can capture video in the H.265-based XAVC HS format (which uses more efficient compression to offer higher quality at the same bitrates). This pushes the burden of decompression onto your computer, but if this is too demanding on your editing machine, the Mark III can shoot All-I footage in the XAVC S-I format. This is less compressed so means bigger files but less processing work for less powerful computers. It’s possible to capture All-I footage at up to 120p if you use the camera’s slow-mo function to reduce the frame rate to 30p or 24p and, therefore, the write-speed to a more reasonable level.
If you need still-more flexibility in your footage, the a7S III can output a Raw stream to an external recorder, over its full-size HDMI socket. The a7S III allows for full-frame (4264×2408) 16-bit RAW output (up to 60p) with a choice of color space; while also recording supported formats internally.
The Mark III also records the information from its gyro sensors, which can be used for applying more effective shake correction when post-processing.
Autofocus
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Another major change in the a7S III is the adoption of on-sensor phase detection autofocus. This is far more useful for video than the contrast detection autofocus used by the Mark II, which inevitably involves racking focus back and forth while recording, which can be visually distracting.
By contrast, the a7S III uses the latest AI-trained phase detection system that can identify and track eyes, faces, heads and bodies of humans, making it generally very reliable when it comes to staying focused on a subject, even if they look away from the camera. There’s also a subject tracking mode if you tap the screen to choose a subject.
That said, we have seen instances of it trying to re-focus mid-clip with static shots featuring subjects who aren’t moving. You can reduce the risk of this by setting the AF Subj Shift Sensitivity, but this makes the camera less likely to refocus if your subject is moving back and forth a little.
So, while lots of a7S users are likely to continue to manually focus their footage, the provision of decent autofocus should extend the types of use the a7S III can be put to.
Card slots
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To accommodate the increased video bitrates, and to make the camera more usable, generally, the a7S III has more storage options than before.
The a7S II had a single UHS I card slot: fast enough for its ~100Mbps (12.5MB/s) max output rate, but without any redundancy or overflow capability. The a7S III has twin dual-format card slots, which can use either UHS II SD cards or CFexpress Type A media in each slot (the connection pins are on opposing sides of the slots, so SD cards need to be flipped over). This provides more shooting options and means that capture at up to ~600Mbps (75MB/s) is possible.
Menus and interface
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One thing that upgraders will notice is that the a7S III features a completely re-worked menu system. The essential ordering and categorization is similar, so it shouldn’t take too much adapting to, but the arrangement is flipped 90 degrees and there are more obvious visual cues to help understand where you are in the menu structure and where the setting you’re looking to change might be.
The camera’s customizable ‘Fn’ menu remains essentially the same but can now be configured separately for stills and video modes, which wasn’t the case on the a7S II. In fact much of the menu system is now separated for stills and video, meaning that your settings for one style of shooting need not carry-over to the other. This makes switching back and forth much faster.
The Mark III also has a My Menu tab, so you can assign the settings you access most often to that tab for quick access.
Better buttons and dials
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Sony’s ergonomic design has come a long way in the five years since the launch of the a7S II. The grips are better proportioned, the dials are better positioned and the buttons are easier to press.
On top of this, the a7S III gains an AF joystick and a much more prominent AF-On button, which can be used to initiate a single AF acquisition when in Manual Focus mode. Collectively, these help add up to a camera that’s quicker and more comfortable to use.
Screens and viewfinders
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Sony has made a lot of the new viewfinder in the a7S III. At 9.44M dots, it’s the highest resolution viewfinder we’ve yet seen, and way beyond the 2.36M dot panel in the a7S II. On paper that’s twice the resolution in each dimension, but the camera only really makes full use of this in playback mode.
For most a7S III users, the bigger difference is likely to be the provision of a fully-articulating rear LCD screen, rather than the tilt up/down example on the older model. It’s a layout familiar to, and preferred by, many videographers.
What’s more, the a7S III finally makes comprehensive use of a touchscreen, allowing it to be used to position the AF point, navigate menus and zoom/swipe in playback mode, providing another means of operating the camera.
Battery
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Another major improvement for the a7S III is the inclusion of a much larger battery than its predecessor. The a7S II is one of the last of the series to use the rather small NP-FW50 battery, whereas the a7S III uses the NP-Z100. This greatly increases the camera’s recording duration. And, while there are plenty of circumstances in which both cameras will simply be powered over their USB ports, the inclusion of a larger, higher-capacity battery means the a7S III can be used for longer as a standalone unit, making gimbal and drone work simpler, for instance.
For photography
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We’ve always considered that the a7S series makes more sense for videographers than stills shooters: the ability to quickly read-out the relatively low pixel count as 4K footage sets the camera apart to a much larger degree than any difference in low light stills performance. It’s no coincidence that this model has the most comprehensive video feature set of any Alpha-series camera, so far.
Stills shooters will certainly benefit from the ergonomic and autofocus improvements of the new camera, along with the revised menus, but we wouldn’t expect the a7S III to offer a significant difference in low light stills performance at anything other than very high ISO settings, thanks to the upgraded Exmor R backside-illuminated sensor and other signal processing improvements.
Conclusion
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It should come as no surprise that the a7S III is a much better camera than the preceding version: the general level of technology has moved a fair way forward in the past five years, particularly in terms of video. And Sony’s ergonomics have certainly progressed a long way in that time, too, with the a7S III moving things beyond any of its recent stable-mates.
But this feels like more than just a camera brought up to contemporary standards. The a7S II was a relatively minor update to the original a7S: the addition of in-body stabilization was a big deal, as was the ability to record its sensor’s output as 1:1 4K rather than the superlative 2:1 1080p of its predecessor. But it always felt like a dependable, but unambitious camera, and its core capabilities were added to mainstream a7-series models within a matter of years.
By contrast, it’s hard to imagine 10-bit capture, 4K 120p, 16-bit Raw video output being extended out across the a7 range so readily, simply because non-videographers don’t necessarily need them. Rather than being a basic video tool whose appeal was its large sensor, the a7S III feels like a much more complete compact video production camera, making it a much more credible rival to the likes of Panasonic’s S1H.
Articles: Digital Photography Review (dpreview.com)