FieldOfView represents the Y angle of view from the bottom of the screen to the top. The default value for FieldOfView is:
FieldOfView = (float)System.Math.PI / 4.0f;
The following diagram shows a side-view of how FieldOfView changes what is shown on screen.
A smaller field of view makes the view more narrow. This narrower view results in the appearance of “zooming in”. Tools such as binoculars or telescopes provide a zoomed-in view by creating a very narrow field of view.
The FieldOfView property is only effective if the Camera’s Orthogonal property is false (the default value).