Zooms in or out in the perspective view by changing the camera field of view.
Zoom operates like changing the lens on a camera. A value smaller than the default is like using a telephoto lens, whereas a value larger than the default provides a wide angle lens effect.
You can use these sliders
to define a view by positioning the camera. The eye position, view
point position, and up vector end point determine the view. These
nine fields contain decimal numbers. They represent, from left to
right, the X, Y, and Z Coordinates for each of the three camera
parameters. To see the camera as you modify it, use WindowDisplay > Toggles > Cameras 
.
The Zoom slider also takes a decimal number which defines the angle of the field of view of the camera. Values must be positive in the range of 0.2 to 179.
