If offline, do the following:
1) Hit F3
2) Hit F8
3) Adjust to the desired angle with the view keys, and the desired distance with the "zoom in" and "zoom out" keys (square bracket keys).
4) Hit the "Toggle gun zoom" key to eliminate the "fisheye lens" effect. This will move you in closer, and you may then need further "zoom in" and "zoom out" adjustments. Without this step, the perspective looks strange if you are close to the plane.