VIDEOCanon's EOS 5D Mark II (introduced in Fall 2008) was the first full-frame DSLR to do video, and it started a DSLR video revolution as pros began using the Mark II for TV and movie work, as well as still photography. (Nikon's APS-C D90, introduced just before the 5D Mark II, was the first HDSLR, but was limited to 720 HD.)
Today, all current full-frame DSLRs except the Nikon D3X (also a 2008 model) can do 1080 full HD video. The primary benefits of full-frame DSLRs for video are the narrower depth of field possible with the bigger sensors (which makes possible that film-cinematic selective-focus effect not possible with smaller-sensor camcorders) and better high-ISO image quality. HDSLRs are also compact and relatively inexpensive compared with pro motion cameras.
With Canon's video DSLRs, you can use contrast or phase-detection AF before you begin shooting, but focus changes during shooting must be done manually.
Nikon's full-frame video DSLRs offer full-time, contrast-based AF while shooting, but it's too slow for many action situations. Sony's SLT-A99, with its unique nonmoving translucent mirror, permits quick continuous phase-detection at all times, for still and video, with eye-level viewing via the built-in OLED electronic viewfinder, which makes it the best bet if you want to do videos of action.
Bear in mind that with all systems, camera noises, including autofocusing, will be picked up by the built-in microphone, so it's best to use an external mic. All of the full-frame DSLRs have a socket for an external stereo mic. On pro movie shoots, focusing is generally done manually, and manual focusing during shooting can be done with all video-capable DSLRs.
CANON EOS 6DCanon's lowest-priced, full-frame model, the 20.2-megapixel EOS 6D lists for $2,099, but nonetheless contains a Canon-produced CMOS sensor and DIGIC 5+ processor that yield (according to DxOMark.com) a tie with the flagship EOS-1D X for best overall image quality of any EOS DSLR. The 6D can shoot full-res images at up to 4.5 fps, and has a normal ISO range of 100-25,600, expandable to 50-102,400.
The 6D features built-in WiFi and GPS. A big pentaprism viewfinder shows 97% of the actual image area, and the 3.0-inch, 1040K-dot LCD monitor provides easy live viewing. While there's no built-in flash, the 6D provides E-TTL II flash with compatible Canon Speedlites.