Focal Speed Introduction

  Optical Speed means how fast a CCTV cameras lens collects lights and is usually described by the f-number such as f/1.2, f/2, etc. This speed can be calculated by the Focal Length and the Diameter(D) of a lens as follows：

f-number = FL/D

  Under the same diameter, Larger FL, higher f-number lens which means lens need less lights to the camera sensor and results a slower lens, Lower f-number lenses need more lights. Larger Diameter, if focal length is fixed, will make f-number lens.

  In summary, the lower f-number, the more lights, the better video picture. The f-numbers are often marked at the iris rings of lenses.