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This handy FOV calculator will help you in determining which lens is right for your application.
Simply enter the distance to the object, camera format Example: 1/4, or 1/3 , and focal length of the lens.
Click "Calculate" to see the field of view you can expect with that lens.
It also works in reverse.
If you know the field of view you need, enter it in and the distance to the object along with camera format to find the focal length you will need to get the field of view desired.
Here is something which is very important to
remember and is a very easy way of thinking about the right Focal length lens.
It is easer to understand this whole field of view thing if you think about it
this way. A wide angle lens at 25' would have a Horizontal field of view
of 33.3' a persons face is only about 8" wide, 8" of a 33.3 foot
field of view is only about 2% of the pixels on that Horizontal line
which means, in the area of the face you only have about 10 pixels . If
a face were 8x8" that's 100 dots. This is about the limit for facial
recognition.
So here is a short cut below. I have identified the major
concerns of people and I have listed the widest horizontal (H) view which is
acceptable given the typical resolution of these cameras.
(if you use a camera with a higher resolution then 270,000 pixels you will have
better recognition performance.
People are usually concerned about four major objects
they want to identify. I have broken them down here.
#1 Facial Recognition. = 25' Horizontal Field of View
#2 Body Recognition (the ability to Identify someone by how tall they are, if
they are male or female, long or short hair and adult or child =25' to 45'
#3 Licenses Plate Recognition (the ability to actually read the license plate
number) =10'
#4 Car Recognition (the ability to type or make of car) = 60'-75'
The function of the lens is to collect light reflected from the scene and focus it into an image onto the CCTV camera sensor.
Most CCTV applications use a fixed-focal-length (FFL) lens, which, like your eye's lens, covers a constant angular field of view (FOV).
S a Fix focal length lens always has the same magnification.
A large variety of CCTV camera lenses are available with different focal lengths (FLs), which will provide different
FOVs (magnification) . Wide-angle 3.6mm, medium-angle 6.0mm, or narrow-angle lenses
12.0mm produce different magnifications and FOVs.
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