It's interesting. I've used differential focus a lot with stills photography. It's one of my main tools, but it never dawned on me that applying it to video ain't quite the same.
This thing could be very useful, there are times when you need to throw a b/ground way out, bring a foreground sharp in, and t'other way round.
I wonder if videocams that use still camera lenses already partly have this capability (?) It's not that straightforward.
For instance, it was clever of Canon to make their EOS SLR lenses adaptable to their XLS1/2 cameras. They cover a 35mm film frame, so there must be a multiplication factor to the size of image they give on the XLS' CCD. (Like a 200mm lens gives the equivalent image size of a much longer FL.)
My guess is that only a limited range of a still lens's full focussing movement could be utilised. My own kit is Nikon, and some JVC cams use these lenses. It would be nice to be able to adapt my hi-spec glassware for video purposes.
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Micro35 
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