zomg I'm such a noob... only last Sunday I worked out - by complete accident - that clicking the right mouse button lets me zoom in/out!

P.S.: the only crummy thing is I can't shoot whilst zoomed in - thus I cannot snipe. At least not with the character I'm currently playing (Sideswipe).

P.P.S.: unless there is a way I can but I haven't worked it out yet! I really should read the instructions.