I'm thinking of getting the lens and the 1.4x or 2.0x extender and wondering if anyone has tried it on their C100, I do mainly orchestral/classical performance video and often want a real tight shot of a performer's fingers on the keys/string, etc from the back of the balcony - maybe 100 feet from the back of the stage.

I've cobbled up a 2x extender on a Mamiya 300mm stills lens with a Mamiya 645 to Canon EF adapter and it works quite well, but of course there's no zoom capability. And a "little bit longer" lens would be nice. And yes, I have to have the camera on a substantial tripod and not move around much to keep from shaking the camera.

I tried the lens on the C100 - works quite well. DP AF works just fine even with a 2X extender (although I think manual focus is better at the extremes since there's a bit of huntig when it looses focus due to slicght movement toward/away from the camera.

All in all, quite usable.