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76 Appendix C: Selecting a lens
object) and the object is 14 mm wide (horizontal size) and 15 mm tall (vertical
size), then the following calculations are used to determine the required focal
length:
×
4.8 mm
52 mm
----------------------------------------- -
14 mm
+
4.8 mm
In this example, a lens with a focal length of 3.47 mm (horizontal) is required.
If the lens has a focal length equal to the focal length of your calculation, you have
the correct lens for your situation. If the lens does not match the focal length of
your calculation, you can still use it. However, if your lens has a focal length smaller
than your calculation, there will be empty space around your object in the image.
If your lens has a focal length greater than your calculation, part of your object
might not fully fit within the image.
and
=
3.71 mm (rounded)
×
3.6 mm
52 mm
----------------------------------------- -
=
3.47 mm (rounded)
15 mm
+
3.6 mm
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