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4.2
Transparent covering
The “window” or transparent covering of an enclosure is usually made of high-quality glass or
durable, polycarbonate plastic. As windows act like optical lenses, they should be of high quality
to minimize its effect on image quality. When there are built-in imperfections in the clear
material, clarity is compromised.
Higher demands are placed on the windows of housings for PTZ cameras and PTZ dome cameras.
Not only do the windows have to be specially shaped in the form of a bubble, but they must also
have high clarity since imperfections such as dirt particles can be magnified, particularly when
cameras with high zoom factors are installed. In addition, if the thickness of the window is
uneven, a straight line may appear curved in the resulting image. A high-quality bubble should
have very little impact on image quality, irrespective of the camera’s zoom level and lens posi-
tion.
The thickness of a bubble can be increased to withstand heavy blows, but the thicker a covering
is, the higher the chances of imperfections. Increased thickness may also create unwanted
reflections and refraction of light. Therefore, thicker coverings should meet higher requirements
if the effect on image quality is to be minimized.
A variety of dome coverings or bubbles are available, such as clear or smoked versions. While
smoked versions enable a more discrete installation, they also act much like sunglasses do in
reducing the amount of light available to the camera. It will, therefore, have an affect on the
camera’s light sensitivity.
4.3
Positioning a fixed camera in a housing
When installing a fixed camera in an enclosure, it is important that the lens of the camera is
positioned right up against the window to prevent any glare. Otherwise, reflections from the
camera and the background will appear in the image. To reduce reflection, special coatings can
be applied on any glass used in front of the lens.
igure 4.3a When installing a camera behind a glass, correct positioning of the camera becomes important to avoid
reflections.
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Glass
BAD
Glass
GOOD
CHAPTER 4 - CAMERA PROTECTION AND HOUSINGS
