Everything's A-4K: Sony Unveils the 4K-Capable A7S

Sony's full-frame mirrorless camera series grows by one with the addition of the 4K-shooting A7S.

The A7S is the first of Sony's mirrorless full-frame cameras to record 4K, though it can only do it to an external third-party recorder. Credit:

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It's not often you see a big name camera announcement on a Sunday, but it's also not often Sony takes its acclaimed full-frame mirrorless camera lineup and adds a model with the ability to shoot 4K video. The groundbreaking camera is called the A7S, joining the existing A7 and A7R and featuring a 12.2-megapixel full-frame sensor that can capture 4K video to a third-party recorder.

The A7S is shaped just like the A7/A7R combination, with a practically identical body and featuring the same powerful Bionz X processor. That combination also yields Nikon D4S-level low light sensitivity, with an available ISO range of 50-409,600 (the standard range is 100-102,400). Sony also claims that this is the first full-frame camera to utilize the full width of the sensor to shoot 4K, without any line skipping or cropping involved.

By reading from every pixel, the camera has more information to work with while downsampling video. Most cameras utilize techniques such as pixel binning or cropping in order to simplify the task of shooting even full HD using a large, high-resolution image sensor. The result of going without these tricks, Sony claims, is video that exhibits fewer artifacts such as aliasing, moire, and false color.

On the outside, the A7S looks just like the A7/A7R. It features the same grip, the same control scheme, and the same ports, including headphone and microphone jacks and Sony's proprietary hot shoe. The camera does feature some extra options inside that Sony normally reserves for its high-end cameras. These include features such as adjustable/savable color profiles (with options for adjusting gamma, black level, knee, detail, and color depth), and clean 4K 4:2:2 output via HDMI. 4K can only be output via HDMI this way, with the memory card being used for stills and HD video only.

Interestingly enough, the A7S also features Sony's S-Log2 gamma functionality. This flattens out the tone curve of the captured footage, extending dynamic range while also preserving tons of latitude for grading in post. Though features like zebra striping have been included in the previous A7-series cameras, a feature like this suggests the A7S is truly designed for professional workflows.

The A7S records video via the XAVC S codec, however, which is the same used in Sony's consumer 4K handycam, the HDR-AX100. It's a lower bitrate than the full XAVC codec used by heavy hitters like the Sony F65, but early tests indicate that it's quite capable (we should have a review of the AX100 shortly, with a better breakdown of performance). The A7S still includes AVCHD and MP4 codecs as well, but XAVC S can be used to record 50Mbps 1080p footage if your workflow can accept it. The A7S can even dual record XAVC S with 1080/30p MP4 footage.

One thing we will have to reserve judgement on is the A7S' focus system. It uses the same off-sensor autofocus as the A7R, which we found less than impressive. It remains to be seen how well the A7S performs, but it's something we're eager to test for ourselves. That said, this should also be a very capable stills camera, with all the same functionality as the A7 and A7R, but with a lower-resolution 12-megapixel sensor.

Pricing and availability are not yet available. We'll have more on the A7S as information becomes available and will have a hands-on report next week at NAB 2014. In the meantime you can get more information about the A7S from Sony's press page.