Outdoor Mounting
If a camera is to be mounted outdoors, an external housing is need to protect it. There are standards that specify the degree of protection to be provided by enclosures. Two digits prefixed by the agreed letters IP define the rating of protection. [ See ]
Camera housings are normally made of extruded aluminium or plastic. Weather conditions dictate if camera housings require a heater, or possibly a cooler. In climates where the weather can vary from bright sunlight to cold and damp there will need to be some form of heater mounted below the front glass plate. This acts as a demister for the glass and prevents the build up of condensation. Washers and wipers can also be added to many external camera housings.
Dome housings are used for external functional cameras because the internal mechanisms can be of a lighter construction and therefore permit very fast speeds of pan and tilt. If the dome is silvered or “smoked” it makes it difficult for a person to detect in which direction the camera is pointing. All material in front of the camera lens will attenuate the light and an allowance of at least one full f-stop should be used in calculating lighting and camera sensitivity.
An auto iris lens should always be used with an outdoor camera. This will give the camera a better dynamic range and protect the image sensor from being damaged by strong sunlight.
If you mount a camera behind glass, for example in an outdoor housing, make sure that the lens is close to the glass. If it is too far away from the glass, reflections from the camera and the background will appear in the image.
Lighting
If cameras are to be used at night additional external lighting will be required. Lamps should be mounted in such a way as to avoid reflections and shadows. Special colour corrected lamps are available which produce a balanced white light suitable for colour cameras.
Infrared illuminators can also be used for covert or semi-covert operation. Normal colour cameras are not suitable for use with infrared illumination. Dual mode “day & night” cameras should be used or traditional (analogue) monochrome cameras can be added to the network by the use of video servers.
Avoid Direct Sunlight
Always try to avoid direct sunlight in an image. Direct sunlight will “blind” the camera and may permanently bleach the small colour filters on the image sensor chip causing stripes in the image. If possible position the camera looking in the same direction as the sun.
When using a camera outdoors, avoid including too much sky in the image. Due to the large contrast, the camera will adjust in order to achieve a good level for the sky and the interesting landscape or objects may appear too dark. One way to avoid these problems is to mount the camera high above the ground. Used a pole or wall mounted bracket and always use sturdy mountings to avoid vibrations caused by strong winds.
The image sensor filters in the camera used to take this image have been destroyed by sunlight
The image sensor filters in the camera used to take this image