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Chapter 2
16
Chapter
17
3
Chapter 3
Positioning the Imager for Optimal Performance
Achieving Optimum Performance
Four items greatly impact performance:
1) Distance (from the scan window) to the bar code
2) Specular Reection; and
3) Quality of Bar Code Labels
4) Imager eld of view and resolution
1) Distance to the Bar Code
The operation of the imager is similar to a camera. If you photograph an object that is
out of focus, the resulting picture will be blurry. The same is true with the imager. If the
bar code label is out of focus, the imager may have difculty decoding what appears to
be fuzzy bars and spaces.
Focal Distance
Ideally, the distance from the window of the imager to the bar code label should be equal
to the focal distance of the imager.
Depth-of-Field
Just as with a camera, the imager has a depth-of-eld. It can read bar codes that are not
precisely at the focal distance - maybe a little closer, or a little farther away. However, if
the bar code label is positioned too far from the focal distance, the imager may not be
able to successfully decode it.
The depth-of-eld varies based on the density of the bar code, i.e., the thickness of the
bars. Very high density bar codes (which have very narrow bars) are readable over a