Just for posterity… it turned out the best solution in my case was the Blackmagic Design UltraStudio Mini Recorder:
HDMI in and output through Thunderbolt. Allows for perfectly clean, undistorted image & video capture.
<p>I'm putting together little tutorials and I need screen grabs of the various menus and live view images as they appear on the camera's screen.<br> What do I need to capture these from the camera's video out port?</p> <p>I have various Nikon and Canon bodies at my disposal.</p>