The website Cameratown has compiled a guide to the various loupes available on the market for HDSLR cameras, such as the Panasonic GH1, Canon D5, Canon D7 and the Nikon D90. Loupes made for HDSLR cameras weren't available when I shot Rejouer, but the GH1 has a flip out LCD screen which helped with certain camera position where a loupe couldn't have been used. However, while shooting in the bright sun outdoors it would have been very useful. If any has used any of these loupes let me know your thoughts.

http://www.cameratown.com/articles/dslr_cinematography.cfm