Any opinions on which focal length/aperture would be best shooting bears in the smokies with a 1.6 crop 40d? Canon 400mm f/5.6 versus 300mm f/4. Yeah I know that distance is desired when dealing w/ a wild animal but generally black bears in the national park are not quite as dangerous as brown bears out west (IMO)... so I'm wondering if I could get by getting the 300mm... the faster shutter the f/4 would allow along with a brighter view really appeals to me (plus greater subject isolation). Of course w/ a full frame camera I'd be looking at getting a 500mm but 1.6x 300 = 480 so maybe this would work. Using a prime lens, I wouldnt want to have such a narrow view anyway and not be able to pull back and compose. Any thoughts?