There are 3 zoom options. The custom zoom option is very powerfull. It is controlled by these parameters in advanced settings:

startZoomDistance 10.0
fieldOfViewNear 45.0
endZoomDistance 50.0
fieldOfViewFar 20.0

In this example, if the model is less than 10 meters from the pilot, the field of view will be 45 degree.
If the model is more than 50 meters, the filed of view will be 20 degree (model will be zoomed)
If the model is between 10 and 50 meters the field of view will vary from 45 degree to 20 degree (variable zoom as model flies away.

You can change these parameters to any model in advanced setting and experiment with the custom zoom.

In addition, F5 zooms in and F6 zooms out.

Stefan
http://rcflightsim.com