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2.7 Detection coverage definition
The focal range of the lens in the camera influences the object size in the picture (please refer
to Figure 2.7-1), actual object height - H, object height on CCD - h, lens focal length– f and
the distance between object and lens - D
t ,
the formula is as below.
D
t
= f
× H / h
Pic. 2.7-1 principle of the image forming
Before calculating the camera viewing scope or covering area, system designer needs to
choose a focal range – “ f ” first, common focal range is as below
：
：
：
：
2.8mm
4 mm
6 mm
8 mm
12 mm
Camera viewable angel and coverage calculation
Different focal lengths in the camera lenses provide different viewable angle and coverage.
Usually it is present in the format of angel. Please refer to Figure 2.7-2
Once the focal length of the lens and the size of the image sensor (CCD) are determined, the
viewable angle of the camera can be calculated. The less the focal length is, the larger
the viewable angle is, with the shorter distance coverage.
Pic. 2.7-2 Camera focal length and viable angel relation
Focal length and viewable angel transformation formula
：
Actual object height
Object height on CCD
Focal range
Distance between object and lens
Lens
