To zoom in, hit the accelerate key, zooming out is decelerate.
Nothing is more painful to a heavy bomber pilot than being spotted because a turret opened fire.
If you're turreting in a heavy bomber, fire only if you know you're seen. Regardless of what the pilot is doing to lower your signature, you will be spotted just inside 2000m from the target, once you're inside this range fire at will. New gunners will often try to shoot the target structure assuming their guns will help lower the shields. First, your gun isn't sweeping for fighters, structures take several missiles and the ship needs to be kept fighter-free to fire them. Second, and this one is a real kick in the nads, you rounds may actually hit your ship's missiles, destroying them.