78 Appendix C: Selecting a lens
For example, your Matrox Iris GTR300 has a 3.0 mm horizontal constant and a
2.3 mm vertical constant. If there is a 52 mm distance between the object and the
front of the lens (distance to the 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:
In this example, a lens with a focal length of 7.34 mm (horizontal) is required.
If the lens shipped with your Matrox Iris GTR starter kits 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
3.0 mm 52 mm×
14 mm 3.0 mm+
------------------------------------------
9.18 mm (rounded)=
2.3 mm 52 mm×
15 mm 2.3 mm+
------------------------------------------
7.34 mm (rounded)=
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