Making the camera zoom in and out?

how would you make a camera that zooms in and out im making a strategy game and i need the camera to zoom in and out how would you do this in script?

So far iv got
`public var fov = 60;

public var fovmax = 90;

public var min =30;

function Update(){

if (Input.GetAxis(“Mouse ScrollWheel”)> 0){

Camera.main.fieldOfView = fov–;

}

if (Input.GetAxis(“Mouse ScrollWheel”)< 0){

Camera.main.fieldOfView = fov++;

}

}
` im going to delete fovmax and min and replace with zoom speed also maybe distance?