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C. Black Spots
These are cosmetic blemishes in the image intensifiers or dirt or
debris between the lenses. Black spots are acceptable as long
as they do not interfere with viewing the image. No action is re-
quired if this condition is present unless the spots interfere
with the usability of the device.
D. Fixed-Pattern Noise
This is usually a cosmetic blemish characterized by a faint hexag-
onal (honeycomb) pattern throughout the viewing area that most
often occurs at high light levels or when viewing very bright lights
(Figure 3-4). This pattern can be seen in every image intensifier
if the light level is high enough. This condition is acceptable as
long as the pattern does not interfere with viewing the image
and usability of the device.
FIGURE 3-4. FIxED-PATTERN NOISE
3-5
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