Focal Length
Focal Length is the distance between the lens and the image sensor when the subject is in focus, usually stated in millimeters (mm).
In what units is fx?
fx : is the focal length expressed in pixel units (as is in the camera matrix).
FOV != Focal Length
The FOV of a camera depends on the focal length of the lens as well as the size of the camera’s image sensor. The relationship between FOV, focal length, and sensor size is complex and can vary depending on the specific camera system.
Various Focal Lengths
Focal Length != Camera Aperture. The thing below is aperture
