The a7S is the third model in Sony's full-frame mirrorless lineup, a 12MP camera that puts as much emphasis on its movie capture capabilities as its still image prowess. While the a7S is a capable still shooter, Sony has emphasized that its real focus (no pun intended) is videography.
The first thing you need to know about the a7S is that it can record 1080p footage internally or be used to output 4K video to an external recorder. The internal 1080p footage is recorded using the XAVC S format, a more consumer-friendly version of Sony's XAVC system. This is the first of the company's cameras to use the format, which frees the camera from the bitrate restrictions of the AVCHD standard.
However, while the a7S's body exactly resembles its original 24 and 36MP sister models, the a7 and a7R (the a7 II's design is slightly different), it includes a whole raft of features and tools to support the videographer. These include the low contrast S-Log2 tone curve that allows more of the camera's dynamic range to be fitted into its video files and the option to record time code. Photographers more interested in stills may wish to note that most of these video features have subsequently been included in the newer a7 II, which also features revised ergonomics and in-body image stabilization.
- 12MP full-frame EXMOR CMOS sensor
- Focuses at light levels to -4EV
- 1080 footage at up to 50Mbps (XAVC S)
- Extensive movie-focused capture options: S-Log2, Black Level, time code
- Video ISO Range 100 - 409,600
- Uncompressed 4:2:2 Full HD and 4K video output over HDMI
- 2.36M dot OLED viewfinder
- Mic and headphone sockets
- 720/120p option for slow-mo capture
- Wi-Fi with NFC
DSLRs capable of shooting HD video have existed for a little under six years. Prior to the Canon EOS 5D Mark II, which demonstrated that you could get near-professional quality video from a stills camera, video seemed to be included on cameras primarily to satisfy a checkbox on the marketing spec sheet. It has subsequently become a critical feature for many users.
For the most part, however, modern DSLRs and mirroless cameras don't offer much support for their video features. The technical capability is there, but even on cameras where a decent level of manual control is provided, tools such as focus peaking and zebra patterhsn that have been standard on dedicated video cameras for many years are often missing. This extends even to cameras such as the Canon 5D Mark II and Nikon D800, whose respective manufacturers are happy to promote video features despite the fact that support for actually using video is somewhat lacking. Canon has subsequently upped its game with the EOS 5D Mark III and the lessons it's learning from the development of its Cinema EOS line, but in general video is promoted much better than it's supported.
The Sony a7S steps around these pitfalls, offering both focus peaking and zebra highlight warnings to help videographers get footage that lives up to the cameras' capture capabilities (you can, however, purchase external monitors that can show the same information on other cameras). They also have add-on accessories available to allow use of industry-standard audio or video connections.
Another shortcoming of many 'HDSLR's is that they capture the relatively low resolutions of video by only sampling 'stripes' of their sensors - a process that's become known as line-skipping. This leads to lower vertical resolution in the video, along with a greater risk of moiré. The a7S avoids this by reading out its entire sensor thirty times per second. And, because its sensor appears to have been designed with video in mind, it's able to intelligently downscale this output into cleaner, more detailed video.
However, just because they go to unusual lengths to accommodate the videographer, this doesn't mean any compromises have been made to the feature sets they offer the stills shooter. Noticeably, the Sony offers the same handling and controls as its more stills orientated a7 and a7R models.
Here's how the a7S sits in Sony's a7 lineup:
|Sony a7S||Sony a7 II||Sony a7R|
|Sensor specifications||12MP full-frame||24MP full-frame||36MP full-frame|
|Video formats||XAVC S, AVCHD, MP4||XAVC S, AVCHD, MP4||XAVC S, AVCHD|
|Highest bitrate||50Mbps (1080p)||50Mbps (1080p)||28Mbps (1080p)|
|ISO Range (Stills)
Standard / Expanded
|100 - 102,400
50 - 409,600
|100 - 25,600
50 - 25,600
|100 - 25,600
50 - 25,600
|ISO Range (Movies)||200 - 102,400
200 - 409,600
|200 - 25,600||200 - 25,600|
|Image Stabilization||In-lens only||In-body||In-lens only|
|S-Log2 picture profile||Yes||Yes||No|
|Electronic first curtain shutter||Yes||Yes||No|
|Battery life (CIPA)||360||350||340|