While Phase One yesterday released Capture One version 6.4 and with it, much anticipated RAW support for new camera models including the Canon EOS 5D Mark III and Nikon’s D800, Canon reportedly is not expected to release the SDK for the EOS 5D MkIII until mid-May, 2012, and until that time full tethered support for the camera in Capture One will not be available.
In the mean time, I have been able to figure out a workaround to at least allow real time viewing of images in Capture One while shooting tethered to a Windows 7 PC:
1) Connect the camera and start EOS Utility
2) In the EOS Uitlity preferences, set the Linked Software as registered to Capture One
3) Set a destination folder in EOS Utility for the image files for the shoot.
4) In Capture One capture preferences, disable tethered support for Canon cameras. This will keep Capture One from throwing an error and hanging when the 5D Mk III is connected.
5) In Capture One, navigate to the destination folder set in EOS Utility in step 3. Images will appear in this folder and as a full preview as they are shot.
NOTE that I have only tested this on Windows 7 64-bit using Capture One 6.4 and the EOS Utility shipped with the 5D Mk III. I will try later to see if I can get the same functionality using the Mac versions of Capture One and EOS Utility on OS X Snow Leopard (version 10.6).
UPDATE: This solution also works with Capture One 6.4 and EOS Utility on OS X Snow Leopard (10.6)