Use the scroll-wh... oh. No idea, sorry. Looks like an oversight, as there doesn't seem to be any keyboard setting for camera zoom. Maybe there's a scroll wheel emulator out there somewhere?
I hate mice Trackballs are so superior for control but mice seemingly have taken over! Last good trackball w/ scroll wheel was the Microsoft trackball explorer and they discontinued those years ago (they now run over $100 on ebay USED!!!).
Anyway, thanks for the heads up, guys... I'll try to figure something out in the logitech software.