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106 Appendix C: Selecting a lens
For example, your Matrox Iris GT300 has a 1/3" sensor chip type (which uses a
4.8 mm horizontal constant and a 3.6 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:
×
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 shipped with your Matrox Iris GT starter kit 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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