Lens Calculator

See Lenses

Example

To cover front of house 15m wide, and camera is mounted 20m back

D = 20

I = 15

20 x 4.8 / 15 = 6.4mm lens approx

To read a car No plate from 20m

(for good evidence the No plate should fill approx 1/3 of monitor, but about approx 20% should be workable)

D = 20m (using 1/3 calc)

I = say 0.5m for width of plate, and fill 1/3 of screen, say 1.5m across

20 x 4.8 / 1.5 = 64mm lens approx

D = 20m (using 20% calc)

I = say 0.5m for width of plate, and fill 20% (0.2) of screen, say 2.5m across

20 x 4.8 / 2.5 = 38.4mm lens approx

Several Zoom cams are available Zoom cams

As can be seen, a strong lens must be used to read a plate at distance.

In ideal lighting and weather conditions, a lesser lens may be suitable to lift the no plate.

How to find the focal length

To find the I width that a lens will cover - approximately

Example 4.3mm lens at 10m away
4.8 x D (10m away) / F (4.3mm lens) = 11.16m wide (approx)

Example 4.3mm lens at 20m away
4.8 x D (20m away) / F (4.3mm lens) = 22.32m wide (approx)

Example 8mm lens at 10m away
4.8 x D (10m away) / F (8mm lens) = 6m wide (approx)