Sony continues to take a three-camera approach with its second-generation full-frame mirrorless system. At one end of the spectrum sits the high-resolution, 42-megapixel Alpha 7R II ($1,798.00 at Amazon) , and at the other is the 12-megapixel Alpha 7S II ($2999.99, body only). The low pixel count goes a long way to improve image quality at extremely high ISOs—the camera can be set as high as ISO 409600—and also improves the quality of 4K video. Our Editors' Choice for full-frame mirrorless cameras is still the Alpha 7 II ($898.00 at Amazon) . This third musketeer in the group features a 24-megapixel image sensor, a low price, and solid all-around performance, but it doesn't support 4K video capture.

Design
The Alpha 7S II shares the same physical design, interface, and controls as its two twin siblings. For information on how the camera handles, you can refer to our review of the Alpha 7R II.

Performance and Image Quality
The 7S II starts, focuses, and fires in about 2.2 seconds—that's slower than the Alpha 7R II, which does the same in 1.6 seconds. When shooting in bright light the autofocus speed is acceptable, if a little bit slow, at 0.15-second. But it slows to just 0.3-second in very dim conditions, which is a fine result. The Alpha 7 II focuses in just 0.05-second in bright light, but slows to 0.7-second in dim conditions. The 7 II uses a hybrid focus system, which incorporates both phase and contrast detection, while the 7S II uses only contrast detection for focus.

When set to Speed Priority mode, the camera can shoot at 5fps. The duration at which it shoots varies based on file format. If you're shooting uncompressed Raw images you can get 25 Raw+JPG or 29 Raw shots before the rate slows. Using the compressed Raw format extends that to 35 Raw shots or 26 Raw+JPG. If you're a JPG shooter you can rattle off 84 Extra Fine or an unlimited amount of Fine JPGs before the Alpha slows.

The 12-megapixel image sensor can be a bit limiting if you're looking to make big prints, especially when you consider that 24 megapixels is the expected norm for full-frame bodies, and that you can get a 42-megapixel Alpha 7R II for a few hundred dollars more.

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But the sensor shines in dim light. When shooting JPGs at default settings, Imatest tells us that noise remains under the 1.5 percent threshold through ISO 25600. What's better is that, even when viewed at 100 percent on a calibrated display, details remain crisp, with just slight evidence of smudging. There's a bit more blur at ISO 51200, but it's not until you push the camera all the way to ISO 102400 that quality seriously drops.

You can squeeze more image quality out of the camera at high ISOs by shooting in Raw. You can see more fine lines in ISO 25600 Raw images, and while ISO 51200 is certainly grainy, details are sharp and crisp. There's a definite drop in fidelity at ISO 102400, but the Raw images are much stronger than JPGs. Even though you can shoot at ISO 204800 and ISO 409600, photos are more noise than information when the camera is set that high. But it's incredible that you're even able to push it that far.

Video
The original Alpha 7S ($1,998.00 at Amazon) captured video in 4K, but only with the aid of an external recorder. The 7S II can also output uncompressed 4K video to a field recorder via HDMI, but it has added the ability to save XAVC S 4K video to a memory card. You can record at 24 or 30fps, with a choice of 60Mbps or 100Mbps quality. When cropped to the standard 16:9 video aspect ratio, the image sensor matches the resolution of 4K video exactly, so there's no need for interpolation, line skipping, or pixel binning—the result is footage that is just fantastic in quality.

XAVC S is also available at 1080p, at 24, 30, or 60fps, all at 50Mbps. These frame rates use the entire width of the image sensor. You can also record at 120fps, at 60 or 100Mbps, but the fame is cropped when doing so. Shooting at a high frame rate allows you to slow the footage down to quarter-speed while maintaining smooth motion. AVCHD and MP4 video is also available, but at lesser quality than the XAVC recording options.

There are a number of video features available that will make pro cinematographers happy. Audio level control is available, as are zebra stripe warnings for blown highlights and embedded time code. You can record footage in a standard color profile, which is ready to share with minimal color correction. S-Log profiles are also available; they capture video with a flat, low-contrast look that is ideal for color grading. And in-body stabilization helps to keep handheld video smooth—you don't have to lock the 7S II down on a tripod, so it can be used for handheld documentary work.

Uncompressed output is available via the aforementioned micro HDMI port. There's also a micro USB connection, as well as headphone and microphone input jacks. Sony sells an XLR adapter for balanced audio input; it mounts in the hot shoe.

Two batteries are included. You can charge a battery in-camera via USB, but Sony also includes an external wall charger, so it's possible to charge one while you use the camera, or charge both simultaneously without buying extra accessories.

Conclusions
Low-light photographers and videographers are sure to swoon over the Sony Alpha 7S II. Its 12-megapixel sensor offers unmatched image fidelity at the high ISO sensitivities you'll use when capturing stills or video in dim light. And the 4K video quality is just phenomenal, whether you're shooting in bright light or dim conditions. But, like the high-resolution Alpha 7R II, the 7S II is a camera that fills a niche. Our Editors' Choice is still the Alpha 7 II—it's a more balanced performer thanks to its 24-megapixel image sensor, and much more affordable at $1,700. But it doesn't support 4K. If that's what you want in a full-frame camera, you'll need to spend more for the Alpha 7R II or the Alpha 7S II.

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