The long promised firmware update arrives just in time for the deadline
Way back in October of last year, Canon promised a firmware update for the 5D Mark III to give uncompressed video out and improve AF performance would be out in April. Yesterday was the last day of the month, and Canon released the promised update, sliding in just before the deadline.
Available to download from here, the firmware brings two substantial updates to the 5D Mark III. Cinematographers will be pleased to know that uncompressed HDMI will now be fed out of the 5DIII while simultaneously being recorded internally. According to Canon, "Combined with an improved color sampling of YCbCr 4:2:2 8-bit video, this firmware update adds efficiency to video editing, improves color grading options, and enhances on-set monitoring."
The firmware update also improves autofocus capabilities when shooting with an extender. The old firmware meant that cross-type autofocusing with the center AF point was only available with a shooting setup where the maximum aperture was f/5.6 or higher. Now, if you're using an extender that knocks the maximum aperture down to f/8, you'll still be able to use cross-type AF. For a complete list of extender/lens combo compatibility, see the chart here.