Frequently Asked Questions (FAQ):  > Products and Applications:
  1. What Is Network Camera and What Are the Advantages?
  2. Which Camera Is Better For My Application?
  3. Is Network Camera difficult to set up?
  4. How Much Hard Drive Storage Space Do I Need?
  5. What Focal Length of Lenses Do I Need?

 

  How to Calculate Lens Focal Length for My Application?  

1) f = v * (D / V)

2) f = h * (D / H)

f : focal length of lens
V : Vertical field of view
H : Horizontal field of view
D : Distance from Lens to Object
v : vertical multiplier (see table below)
h : horizontal multiplier (see table below)

Camera Format 1/3 inch 1/2 inch 2/3 inch 1 inch
v 3.6 4.8 6.6 9.6
h 4.8 6.4 8.8 12.8

For Example:

To calculate focal length using:

1/3 inch camera h = 4.8
Horizontal field of view H = 12 feet 
Distance from lens to object D = 100 feet

substitute these data to formula  #2 above:

f = 4.8 * (100/12) =  40 mm 

Therefore, it would need a lens with focal length no longer than 40mm to cover a 12 feet horizontal field of view (H-FOV) area completely -- from 100 feet object distance with 1/3" format camera; i.e. using a 60mm lens from 100 feet, it would be able to achieve only 8 feet H-FOV, On the other hand, a 30mm lens would be able to cover 16 feet H-FOV from 100 feet away. 

Note: field of view (V or H) and object distance (D) can be in any units of measure, provided they are both the same.