For the most part, this site concentrates on the still capabilities of mirrorless cameras. Virtually all of these cameras have video capabilities, though, and some are quite good.
If video is important to you, you need to look at several things about these cameras that I don't tend to write about much in reviews:
- Lens motors. Some lenses are better for video use than others. In the m4/3 world, they tend to call lenses designed for video use with the moniker MSC. But what's that really mean? Why would a lens be different for video versus stills? First, continuous focus performance is usually optimized. That typically means a faster autofocus motor in the lens, one that can quickly change direction of focus quickly. Second, video-optimized lenses are quiet so that focus and zoom sounds don't actually get picked up by the microphones recording the audio for a video clip. The 10-100mm Nikkor for the Nikon 1 system is eerily quiet, for example, while the kit lens (10-30mm) can make enough noise to be heard by the camera's microphone while focusing, plus when you manually zoom it you may make enough noise to be picked up, too.
- Lens speed. One of the draws of using a mirrorless camera for video is that most have a fairly large sensor, and with the right (fast) lenses, you can get Hollywood-like focus effects. What's that mean? It means backgrounds (and sometimes foregrounds) thrown out of focus. The small sensors used in many video cameras, even professional ones, have historically provided more depth of field than Hollywood film cameras. But an APS sensor is almost the same size as the typical camera used on a feature film, so with decently fast lenses (f/1.4 to f/2.8) it can mimic the looks that the Hollywood directors of cinematography get. On a m4/3 body, with its slightly smaller sensor size, you typically need faster lenses to get the same effect (e.g., the 25mm f/0.95 Voigtlander, or any of the f/1.4 lenses).
- Audio capabilities. Almost every camera has in-camera microphones, but these coupled with "Auto" recording levels will just cause you frustration. Look for cameras with an external microphone capability and the ability to control audio gain. If the camera doesn't have the latter, then you might need to run an external microphone through an external mixer prior to connecting it to the camera (e.g. Beachtek, Silicon Designs, etc.). Some videographers just do the Hollywood thing and use separate audio equipment. A really good digital audio recorder is surprisingly inexpensive, and it's relatively easy to combine audio and video output with third-party software, such as Pleural Eyes.
- Manual video control. One thing that runs throughout all the video advice is the fact that videographers need more manual control over things. If you use auto audio gain, auto white balance, and auto exposure you'll find that you'll have a difficult time keeping transitions (edits, dissolves, etc.) from being "jarring." Any change across scene cuts that's not controlled by the videographer is asking for viewer disruption. Most videographers, therefore, want to control exposure and white balance manually. Indeed, the high-end ones want to control even more than that, including gamma and other settings. Only a few of the mirrorless cameras have full manual video control (e.g. GH2, GH3, GH4, V1, V2).
- High bandwidth. Virtually all video (and all still camera video) is compressed. Just like JPEG compression throws out data, all the video compression schemes throw out data. In fact, some throw out so much data that you can see clear differences between outputs. Compression is sometimes referred to in bandwidth terms (how much actual data is in the video stream), such as 18Mbps. A little math: 1080P is basically equivalent to 2mp. 2mp times three 8-bit colors (RGB) is 6MBs of data per frame. 30 frames per second is 180MBs of data. Thus, 18 megabits is a pretty severe compression: for every bit we have left, we originally had 60. The way most of these compressions work is that there's a key frame that's recorded something akin to what JPEG might give you, then only differences in subsequent frames are saved, and even those tend to be compressed. That's a gross oversimplification, but the point I'm headed towards: more bandwidth is better. If you have the choice between two cameras, one that records 18Mbps and another that records 24Mbps, and all else is equal, you're going to want the one that uses the higher bandwidth. AVCHD, which most of these cameras use, originally had a maximum bandwidth of somewhere around 24Mbps, which was an attempt to make sure all Blu-Ray equipment could keep up with it. Things have changed since the original definition, and there's now an AVCHD II, plus hackers have come up with all kinds of other compressions on the GH2, some hitting bandwidths higher than 100Mbps. The terminology gets confusing, though, so I suggest you just look at what the maker says the output is at its highest quality and use that as a general guideline for what the quality might be between two models.
- Rolling shutter. Here's the dirty secret of still camera video: it doesn't pull off all the data for a video frame at the same time (there are some exceptions—the Nikon 1 seems to come close). Instead, they pull off rows of data at a time, in sequence. But what happens if something that covers much of the frame moves between those row grabs? The object gets slightly offset in each subsequent row. We call the technique to grab sequential data "rolling shutter," and some cameras are far worse at this than others. One hint at how well it might do is what its maximum frame rate is. A camera that can perform 1080P/60 tends to have fewer rolling shutter impacts than one that can only do 1080P/30 (it's implied that the row grabs can be 2x faster). That's not perfectly true of every implementation, but it's a reasonable guideline. That said, rolling shutter seems to go away more and more with each generation of sensor.
In terms of mirrorless cameras that work well for video, there's one elephant in the room: the Panasonic GH2. The GH1 (later replaced by the GH2, GH3, GH4, and soon the GH5) and the Canon 5DII became quite popular with videographers, partly because they have so many video features in them, but also because they create very good quality video images, and especially because both cameras have been hacked to add even more video friendly features. The GH4 ships with a number of small things that make it handy for video, including a cropped-video ability that pulls direct pixels off the sensor and provides some stunning "telephoto" video capabilities. Beyond that, it had excellent compression from the get go, but the video hackers managed to come up with even better implementations that run on the stock hardware. There's plenty of manual control on a GH4, as well (at least if you can figure out the absolutely opaque manual). More so than any other mirrorless still camera, the GH4 excels at video work.
That's not to say that the rest can't be used for great video. I've seen plenty of video examples off of virtually all the mirrorless cameras that stand up against work done with pro video equipment. It's just that the fewer of the things I mention above that are in your mirrorless camera, the harder it will be to create great videos with them. That said, I've used a Sony NEX-5 for theatrical work and a Nikon V1 for wildlife work with success. Another big plus: these are small cameras and can often be put just about anywhere.
You may have noted that I wrote "mirrorless still camera" a couple of paragraphs ago. Does that imply that there are mirrorless video cameras?
Technically, all video cameras with interchangeable lens mounts are "mirrorless," as no video mainstream video camera uses a mirror the way still cameras do. But Panasonic and Sony have come up with video cameras that use their mirrorless still camera mount.
In the case of Sony, they have a lineup from prosumer video camera (VG-30) to professional (FS-700) to high-end professional (FS5) that can all use the E-mount lenses. I personally use an FS-100, and I'm comfortable in writing that it's good enough that I'll never shoot 35mm movies again. It's a strange beast in terms of design—as are most professional filmmaking and video cameras—with more buttons and controls on it than you can count on a big family's hands. But in serious video work, there's usually more than one person at the camera (director of photography, camera operator, focus puller, maybe another grip or two). Things work differently in the pro world (and more slowly) than just trying to take some video of junior's birthday party. Everything is controlled, and you need to be able to see what those settings are quickly and visually.
The FS-100 uses a relative of the NEX-5N sensor, but one optimized for video (less rolling shutter, for example). That's true of the Panasonic camera, the AG-AF100: it uses a relative of the sensors used in the GH series, but again one tweaked to get top notch video out of it.
So here's my advice:
- You do pro video work. Jump right to a real video camera. It's out of the realm of this Web site to say whether that's a RED Epic, a Canon C300, a Sony FS-700/FS5, a Panasonic AG-AF100, or something else, but you need and will appreciate something that was designed for video and is high performance. That's not to say that you wouldn't sometimes use a mirrorless still camera for a second camera, a disposable (in jeopardy) camera, or for shots that are in tight spaces or need to move freely. But your choice of a small still camera for video would likely follow what you got for your primary camera (if for no other reason than to share lenses).
- You're a budding videographer. This is where something like the GH4 looks very appealing: it has real video credentials, it's not overly expensive (cheaper than prosumer camcorders), and it'll produce output that's more than usable. No other mirrorless camera currently comes close, in my opinion, though the Nikon V1 might be better for some types of action shots due to its great focus system.
- You want to dabble at a little video. All of the mirrorless cameras probably have enough video capability in them now to satisfy you. You probably don't really need 1080P; solid 720P works just fine for most uses, and virtually every camera can produce it. Look only at the features I list at the top to narrow down between two cameras if you need to, but don't get overly anal about that. In other words, if you're in this category, the video capabilities aren't likely to be the deciding factor of which camera you pick.