The a7s is an interesting addition to Sony’s new line of full-frame cameras. It follows the standard a7 entry-level full frame camera and the a7r. Just as the ‘r” in a7r stands for resolution—as in high resolution—the “s” in a7s stands for sensitivity. In fact, the a7s puts such a focus on low light sensitivity that it results in some serious trade-offs in resolution.
The a7s is a 12.2 megapixel low-light sensor, which essentially amounts to 4K. That’s not great resolution for photos, but this version of the a7 clearly was meant for video recording in as many situations as possible. While the camera can natively record 1080p video to an SD card in a variety of formats, it cannot record 4K without an external device that costs nearly as much as the camera body itself. This is unfortunate, and a little silly, since the camera supports Sony’s XAVC-S codec for higher bit rates, which it users in its 4K prosumer camera, the FDR-AX100. That said, the a7s can output both 1080p and 4K uncompressed through the mini HDMI port. That’s great if you still have two grand left over after buying the a7s and really need that added video quality.
Lens Options, Problems, and Solutions
That said, you’re in for another disappointment when it comes to lenses. Sony released five relatively expensive full-frame e-mount lenses that work natively with their a7 line. While some have received better review than others, the worst of the bunch starts at $500 and you can expect to pay as much as $1500 for the higher-end glass. Those prices shouldn’t come as a surprise for both Sony fans and professional photographers alike, but the lenses offer relatively slow apertures for their class.
You might think you can overcome that problem by purchasing standard e-mount lenses, but there’s a serious trade-off. Standard e-mount lenses either offer some pretty insane vignetting or require you to crop the sensor significantly. On a camera like the a7r, this crop makes for smaller but still usable images. On a lower-resolution camera like the a7s, however, they’re just a hair above 1080p. Images that small are virtually unusable, and if you plan to record 4K video with the a7s you’ll barely get anything of value when using a standard e-mount lens.
The good news, however, is that you can adapt all sorts of lenses to the a7s without any trouble. Sony’s LA-EA4 adapter—which costs about $350—allows the use of Sony A-mount lenses with full autofocus capabilities and no need for APS-C sensor cropping. Samyang/Rokinon also provide inexpensive, quality manual focus lenses that work well with this camera. If that’s not enough, you can pick up inexpensive adapters for older manual focus lenses—like Nikon—and you’ve got a cheap way of overcoming the annoying APS-C crop factor. None of these are perfect, but it’s an issue Nikon and Canon both have with their specialized APS-C lenses as well. Unfortunately for Sony, they don’t have quite the large range of full frame-compatible lenses that you get with many other manufacturers. Hopefully we’ll see more in the future.
Image and Video Quality
If you’re buying this camera, you probably don’t care too much about the drawbacks and are more interested in the video and images this camera can produce—notably in low light. Fortunately, there’s a lot to like when it comes to quality. The a7s can see in the dark, and does so with reasonably low noise levels. At high ISOs, it retains detail better than the Canon 5D Mark III, as evidenced from DP Review’s direct tests, as well as my own casual testing. Furthermore, it produces beautiful images with great detail and color even in poor lighting situations. Video quality is pretty much identical to the images the camera captures. It’s very clear Sony intended to make a video camera that looks like it was intended for photography.
Video Codecs and Frame Rates
You get a lot of choices with your video, too. Although the AVCHD codec provides relatively low bit rates of 24-28mbps, XAVC-S nearly doubles it with 50mbps for all 1080p frame rates. Additionally, you can record at 120fps at 720p for some nice slow motion and can dually record 720p video as a reference when creating a higher quality file. While XAVC-S is a marked improvement, the a7s provides just half the bit rate of Canon’s 5D Mark III. The codecs are different, so how this actually affects the quality remains to be nitpicked. Besides, if you’re buying the a7s for its uncompressed output this is pretty much irrelevant anyway.
The inner-workings of the a7s certainly has its major advantages and drawbacks, but on the outside it looks and feels fantastic. I’ve always found Sony’s mirror-less cameras to have excellent build quality, but the a7s seriously raises the bar. It looks great, it’s hardly much bigger than its mirror-less siblings, and has several intelligently-placed buttons and dials. You can set custom functions, make small exposure adjustments, and access manual settings without the need to dive into any menus—most of the time, at least. The camera and its lenses are also weather-proofed so a little rain isn’t going to kill it. It also features an articulating LCD screen and viewfinder so you can pretty much see what you’re shooting any way you want.
Sony advertises battery life at 320 shots. They don't mention how that translates to video, but from what I've seen so far it's looking like a little over two hours on a single charge. Sony seems to have realized battery life is an issue with the a7 line and included multiple charging methods. Not only does the package include an external battery charger, but you can also just plug in the camera via USB. Despite the ongoing need to buy peripherals to get the most out of the a7s, at least you don't have to when it comes to your batteries. On top of that, my a7s included two batteries so I can have one charging and one active. According to the manual and everything I've read, I was only supposed to receive one. I'm not yet certain if this was my luck or an intentional last-minute addition.
The good news? It might not be shooting photos and video that sucks up the battery life. Most of Sony's cameras now have wireless features and NFC, which apparently contribute to the problem. Users of the a7 line have reported that enabling Airplane Mode allowed for many more shots. I have yet to confirm this, but some users are reporting more than four times what Sony claims the battery can handle.
The Bottom Line
Overall, the a7s offers a series of compromises. You can get some great video and images in just about any lighting situation if you’re willing to sacrifice resolution. For some, these trade-offs are essentially meaningless. I’m one of those people. For those who want a camera that handles photos and video in low light at high resolutions in a tiny package—well, that’s too much to ask right now. With Sony, you have to sacrifice one of those things. If you can pick one, they make an a7 model with compromise of your choice.