Focal Length:

The focal length of a lens determines the field of view at particular distances, The Focal Length is measured in mm, there are many size of theme like 2.8mm, 3.6mm, 4mm, 12mm, 16mm ………100mm.

The concept of theme is:

• A short focal length (e.g. 2.5mm) = a wide angle of view.
• A long focal length (e.g. 16mm) = a narrow angle of view.



2.5mm it will give 120 degree
3.6mm it will give 92  degree
4mm    it will give 78  degree
6mm    it will give 53  degree
12mm  it will give 25  degree
25mm  it will give 18  degree