When to use: Select the right lens focal length for a camera by computing the horizontal, vertical, and diagonal field of view from the lens focal length and the imager (sensor) size. FOV = 2·atan(sensor / (2·f)). The coverage width at the target distance and the resulting pixel density determine whether a scene supports Detect, Observe, Recognize, or Identify per the EN 62676-4 DORI criteria.