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The inspection system design
follows the same algorithm as
a human inspector; ignore the
great body of the material and
concentrate on the
exceptions (defects). The
choice of this optical system
depends on the nature of the
defects, for a given
application.
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Bright Field and Dark Field
Most of the time, defects may be segmented into two optical classes, bright
field and dark field. Bright
field defects change light intensity,
i.e., contaminants, pinholes, stains, coating voids, etc.
Dark field defects change light direction
(refraction), i.e., clear gels, coating disturbances, optical power
changes, etc. or coherence (diffraction),
i.e., scratches, streaks, hardcoat cracks, etc.
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