It's either a hemispere or patent issue.
sorry this is going to sound weird, but i've noticed that for some lenses you turn the wheel clockwise to zoom in (e.g. for the Nikon D70), whileas for other lenses (eg Canon)you turn anti-clockwise to zoom in.
i'm more used to the anti-clockwise way, and was wondering then if i need to buy a Canon camera in order to do so. in other words, i probably can't use a Canon lens on a Nikon camera right?
do different brands have different turn directions?