Focal Length and Angle of View

  For a thin double convex lens, all parallel rays will be focused to a point referred to as the principal focal point. The distance from the lens to that point is the principal focal length of the lens. focal length play a role part to ascertain the angle of view of a lens. For instance, 1/3" sensor format with a 6.0mm focal length lens has 56.8 degree of diagonal angle of view, however, the same 6.0mm focal length lens on 1/2" sensor format is 75.5 degree. Each manufacturer has different angle of view of the lens.

  Take 1/3" CCD chip camera for example, the formula below is a simple way calculate focal length of a lens we need

(Distance to subject / Width of subject) x 4.5mm = Focal Length.

  For example, if you use 1/3" CCD CCTV cameras to watch a item with 5.5ft width at 10ft distance, you will use a 8.0mm focal length lens. That is to say, 10ft / 5.5ft x 4.5mm = 8.18mm. A 8.0mm FL lens can meet your requirement