D-SLRs + HD Video
New cameras from Canon and Nikon are the first SLRs to include video
There are two distinct limitations of HD video. The first is limited recording time, and the second is that you can’t use autofocus while shooting video. For the Nikon D90, there are no official specs released for how long you can record HD video, and for the Canon EOS 5D Mark II, manufacturers expressly say that it can record up to 4 GB of full-resolution 1080 video or just under 30 minutes, whichever comes first.
The reason for this limitation is that the image sensor is continuously recording and converting available light from an analog to a digital signal, which taxes the sensor and causes it to overheat. When a sensor overheats, it introduces noise, and the processing system becomes overloaded, which puts a limit on how much video you can shoot. As sensor and processor technology advance, expect to see improvements in this area.
Autofocus also isn’t possible with either the Nikon D90 or Canon EOS 5D Mark II—the AF system is disabled because the mirror is moved out of the way, and as mentioned before, autofocus systems require the mirror. Since autofocus is disabled, these two cameras allow you to lock focus only before you start the movie mode in both cameras. You can manually focus your lens with a lens-focus ring while shooting, though this can be very difficult to perform successfully, and practice will definitely be required for good results.
Canon’s EOS 5D Mark II can shoot 16:9 full HD video with stereo sound, featuring 30 fps shooting, a built-in microphone and a jack for an external one. The 5D Mark II also can shoot standard-definition video and can use the 60 different lenses available in their EF lens lineup.
The Nikon D90 shoots video at a lower, yet still HD, resolution (1280 x 720), and has great features like a built-in mic, 24 fps capture, which mimics cinematic cameras and also can shoot standard-def video. You also can use any Nikkor lens with the D90.
Though D-SLRs aren’t likely to replace video cameras in the near term, it’s interesting to see HD video turn up in a still camera. The trend had seemed to point to video cameras with still capability giving still cameras a run for their money, but with the ability to capture motion video and use interchangeable lenses, the game is back on. We’re interested to see where this goes, as D-SLR makers tackle the limitations and further blur the lines between photo and video.