30
Technical Reference
Field of View and Focal Length
Depth of Field
(1) How to calculate the fi eld of view
If the distance to the object is fi nite, you can use the
following formula to calculate the fi eld of view.
(2) How to calculate focal length
If the distance to the object is fi nite, you can use the
following formula to calculate the focal length.
Example
A 1/3" CCD camera with an 8 mm lens is used,
and the distance to the object is 3 m. The maximum
horizontal width as viewed on the monitor can be
calculated as follows.
Example
A 1/3" CCD camera is used, and the distance to the
object is 3 m and the horizontal width of the object is 2 m.
The focal length to capture the complete object size can
be calculated as follows.
Y ： Object size
Y' ： Image size
L ： Object distance
f ： Focal length
Y' ： 4.8
L ： 3000
Y ： 2000
Y' ：4.8
L ： 3000
f ： 8
f
L
Y′
Y
Horizontal width 1.8 m
Focal length approx. 7 mm
Tr
Tf
The depth of fi eld can be calculated by
the following formula.
When focusing on a certain area in front of and behind the
deep object appears in focus. This area is called the depth
of fi eld. This is because the focus appears sharp if the focus
misalignment is under a certain volume. This certain volume
is called the permissible circle of confusion.
The depth of fi eld has following properties.
1) The larger the F No. is, the wider the depth of
fi eld becomes.
2) The shorter the focal length is, the wider the
depth of fi eld becomes.
3) The longer the distance to the object is, the wider
the depth of fi eld becomes.
4) The backward depth of fi eld is wider than the
forward depth of fi eld.
Image sensor
Permissible circle of confusion
1"
0.03 mm
2/3"
0.021 mm
1/2"
0.015 mm
1/3"
0.011 mm
1/4"
0.008 mm
Backward depth of fi eld
f: Focal distance
F: F No.
: Permissible circle
diameter of confusion
L: Object distance
Forward depth of fi eld
Depth of fi eld
Focal depth
Depth of fi eld
Focal depth
Permissible circle
of confusion
