Glass vs Digital Zoom

This morning I was shooting a double video with my Cinevate FrankenMedusa rig. Up top I had a Canon 5D Mark 2 with a Canon 135mm mounted, and below a Canon 7D with a rather elaborate telephoto setup of a Canon 100-400mm zoom lens with two stacked Canon teleconverters: 2.0 and 1.4. Factoring in the 1.6 crop factor of the 7D and the equivalent focal length of all this glass on the 7D totals up to 1,792mm!

However.....when I was aligning the upper and lower cameras using a distant hydro tower as a reference target, I was a little startled to see that the 5D/135mm was showing a clearer image in the LCD when multiplied by 10x than the straight 7D LCD image at 1,792mm. Hmmmm. I shot some footage with both cameras and got the results here:

Telephoto Glass vs Digital Zoom from David Rilstone on Vimeo.

As I mention in this video, the heavy glass gives a much sharper image than the short 135mm glass getting jacked up by 600% in post.