This might earn me stupid question of the week honors, but reading this question made me wonder whether it would ever make sense to use a astronomy telescope + camera mount as an earthbound zoom lens?
I assume they are "slow" but can they focus? It seems they might be useful in certain circumstances, such as shooting shorebirds such as terns and gulls which typically stand around without much movement.
EDIT - ok I got my terms confused here - I meant telephoto not zoom. I was thinking of the utility of a telescope used as a telephoto prime lens versus a made-for-cameras telephoto prime lens. They surely provide differing characteristics with respect to price, aperture, and distance?