The Sony a7S II follows hot on the heels of its sibling, the 7R II.

While the latter ($4,099, body only) caters more to still photographers, the a7S II aims to appeal to videographers who need high sensitivity of up to ISO 409,600 for 4K (3,840 x 2,160) video recording.

It is easy to mistake the two cameras for each other. They look alike and both are well-designeda, although the aa7S II has a more pronounced rubberised grip. It also has a contoured rear thumb rest that makes for a more secure hold on the camera. Build is solid and sturdy, thanks to a magnesium alloy shell.

Button layout is well thought out, with all the important controls and buttons within easy reach for quick changing of settings.

Compared with the original a7S, this Mark II version sports several improvements. They include an increase of contrast autofocusing (AF) points from 25 to 169, direct recording of 4K video into memory card (previously you needed an external HDMI recorder device), and a new five-axis optical image stabiliser.

aIt can record full high-definition (1,920 x 1,080 pixels) videos at 120 frames per second (fps) in full-frame format, which can be edited to 4x/5x slow-motion videos at 24 or 30fps. This camera is the first in the market that allows in-camera editing of 120fps videos to 4x/5x slow-motion videos.

The a7S II is fast when starting up and shutting down, taking only 1.2sec for each function. Most mirrorless cameras require around 2sec.

Using a Sony FE 28-70mm f/3.5-5.6 lens, the camera achieves focus lock almost instantaneously in bright sunlight. In dim conditions, it usually takes around 1sec to secure a focus with the aid of AF assist light. In video mode, it takes a quick 1.5sec for it to refocus when panned from one scene to another.

Image quality is great. Details look sharp down to the pixel level, while colours are vibrant and there is good dynamic range. But due to its relatively small megapixel count, details are lacking when enlarged.

Video recordings, whether in full high-definition or 4K, are crisp and do not suffer from too much ambient and wind noise.

In terms of its ability to curb image noise at higher ISO levels, this camera is a spectacular performer. There is no noticeable image noise until ISO 6,400, with loss of details becoming really evident only at ISO 25,600.

Even at a whopping ISO 51,200, images are still acceptable for posting on social media. But anything above that looks water-colourish. For still photographers, the superb image noise performance might just be the reason to get this camera, over the a7R II.

However, the a7S II does not support Cinema 4K (4,096 x 2,160 pixels) video recording. Given that it is a video-centric mirrorless camera, this exclusion is a tad puzzling.

The aa7S II suffers from the perennial mirrorless camera problem of poor battery life: It takes only about 310 still images and 60min of videos.

• Verdict: For videographers looking for something compact and lightweight to shoot 4K videos, the Sony a7S II is the camera to get. Just get more spare batteries.