The Sony Alpha A7s is a mirrorless system camera with a full-frame sensor. Announced in April 2014 it comes six months after the Alpha A7 and A7r, with all three sharing the same compact body, FE lens mount and full-frame sensor size. What makes the A7s different from its siblings is its resolution and video capabilities.
Where the A7 and A7r deliver 24 and 36 Megapixels respectively, the A7s offers just 12. The lower resolution of the A7s gives it greater low light performance with a huge maximum sensitivity of 409,600 ISO, but as importantly it allows the sensor to capture 4k UHD video at 24, 25 or 30p without downsampling; this in turn eliminates moire and other scaling artefacts which plague models with higher resolution sensors. Sadly unlike the Panasonic Lumix GH4 though, the Alpha A7s can’t record 4k video internally. Instead it’s output over a Micro HDMI port in 8 bit 4:2:2 format to an optional external recorder like the new Atomos Shogun, itself costing around $2000. Offering some consolation though is the 1080p video which enjoys an upgrade over the A7 / A7r thanks to an absence of scaling artefacts (1080p simply involves halving UHD in both axes) and a higher quality XAVC codec operating at 50Mbit/s. The A7s also offers 720p in an APS-C cropped mode at up to 120fps.
Beyond the sensor and internal electronics, the new Alpha A7s is essentially the same as the A7 and A7r. As such it enjoys an XGA OLED viewfinder, a 3in tilting screen and a compact body. The AF system is a basic 25 point contrast-based system, so sadly no phase-detect AF built-into the sensor, but it does work at low light levels down to -4EV to complement the incredibly high sensitivity.
The Alpha A7s was launched at the NAB show in Las Vegas, where the B stands for Broadcasters. This is a show about video, and as such the A7s’s 4k capabilities were the headline grabbers. Of those I spoke to in the broadcast and movie industry, the inability to record 4k in-camera isn’t that big a deal as most professionals would be looking to couple a camera like this with an external monitor and recorder anyway. Sure it increases the working cost of the A7s by around $2000, but probably the biggest issue in this regard is the use of a Micro HDMI port on the body which isn’t exactly ideal for heavy use and abuse.
But it does give the rival Lumix GH4 a big advantage as not only can it record 4k internally, but it also outputs a higher quality 10 bit 4:2:2 signal through its HDMI port, plus it’ll encode 1080p at higher bits rates up to 200Mbit/s.
But most people will be looking at the sensor sizes and lens options. The full-frame sensor in the A7s doesn’t just make it better in low light but gives it great flexibility with the option to deploy ultra-fast options without a crop. Sony’s also stolen an important lead on Canon here which currently only offers 4k on much more expensive products. Presumably a future 5D Mark III would offer 4k, but it’d be bigger and heavier than the A7s. Ultimately there’s pros and cons to both the Lumix GH4 and Alpha A7s, but it’s incredibly exciting to have two sub-$2000 bodies which can capture 4k without scaling.
As a stills photographer though I’m fascinated by the potential of the A7s. While most manufacturers have slowed down on deploying ever-higher resolutions, there are those who’d simply prefer a big sensor with a lower resolution than even the Canon 1Dx or Nikon D4s. Something like Canon’s original EOS 5D has regularly been cited as a perfect combination of sensor size and resolution, but what we really want is this specification on a modern sensor. Well now Sony’s given us it with the A7s: a brand new sensor with full-frame dimensions and a sensibly low resolution. In a way I’m pleased they’ve left out the internal 4k recording as it’s kept the size and cost down for still photographers who only want that nice big pixel pitch. Equally I’m disappointed Sony didn’t take the chance to embed phase detect AF points as good as the A6000, which could have made the A7s a very capable sports camera, but we can’t have everything.
I’ll leave my video friends to investigate the movie capabilities of the A7s, but when I get my hands on it, I’ll be looking at its potential for low light stills. I love that Sony now offers three versions of the Alpha A7 with 36, 24 and now 12 Megapixels and I can imagine many owners of, say, the A7r complementing it with the A7s for the best in resolution, noise and video. I’d love to hear what you think!