Hi Morton, I suggest you go out there and give it a try, prolly the best way to find out exactly what will be achived with said scope & dslr ? These guys videoing wildlife have some pretty expensive gear, the price you pay for quailty, some of the rigs/gear you see behind David Attenborough is just insane ?
I have the 600D and am not real familiar with Vid capture yet, though i think this camera wont do 'continuous' focusing in Vid mode, not 100% sure yet as I,ve only used vid a few times ? Though I have done quite a number of terrestrial photo's with the ED80 & ED100 @ 600mm & 900mm respectively on Birds and Surfers, pretty happy with the results, see attached, Surfer taken with ED80 F7.5 !
Only initial hassle was Holding these sized scopes in one hand, operating the shutter etc with the other and then growing a third hand for manual focus of the scope
Actually focus was more a guessing game to predict where focus was relitive to when you wanted to shoot, kinda thing.
Another thing is that both my ED's have the little camera piggy adapter on the top of one of the tube rings in which I fit the Camera's Tripod foot and attach the scope up-side-down to the tripod, keeping in mind to move said scope ring to a close ballance point. Scope being upside down also allows one's shutter finger to reach the focus knobs more easierly
Other than that, Someone may know a bit more about Vid capturing ?
Anyway, hope this helps