SEM Security Systems
a division of Southeast Mobility
Cameras come in a variety of shapes and sizes but regardless of how fancy the
advertisement looks, they all work basically the same. Some things to compare
are resolution, lens, and lux.
Most of the cameras out there are analog cameras however high definition (HD)
cameras are beginning to proliferate the market. Analog cameras measure
resolution in TVL or tv lines. Not long ago 380 lines was pretty much the standard,
now a days 500 to 600 lines is common place and there are some that claim even
higher tvl. Depending upon you application, 380 lines may be acceptable, higher
resolution costs more money so each application has to be evaluated.
HD cameras measure resolution in pixels, the higher the megapixels, the clearer
the picture. If you have watched any of the investigative shows on television you
have seen them zoom in on a camera and read a tag number on the other side of
town. This isn't going to happen with an analog camera, sorry. With an HD camera
however, it is possible. HD cameras can allow you to blow up a picture and read a
tag number across the parking lot in clear detail.
So why don't we just use all HD cameras? The most obvious reason is dollars. HD
cameras cost 7 to 10 times as much as a good quality analog camera and 20
times as much as a cheap analog camera but there are other costs as well. All
that resolution has to be stored on a hard drive somewhere and it takes much
more drive space to store the video from an HD camera than it does an analog
camera. HD recorders are more expensive than analog and the increased drive
space requirements increase the costs even further.
Another thing to watch out for with HD cameras is that at this time there is not
standard that everyone adheres to. You can use anyone's analog camera with
anyone's recorder, not so with HD. If you want to use an HD camera, you must
make sure that it is compatible with the recorder that you are planning to use.
One more word of advise, avoid purchasing a boxed system with cameras that use
a molex plug that carries both power, video, and audio. While that makes the
system easier to install, you are stuck with whatever cameras that are available
from that vendor, and the choices are usually very limited. You want a camera with
a BNC connector for the coax and wire terminals for the power. Decent quality
cameras seldom come with audio built in. Using this type of setup allows you to
switch and swap cameras at will. Need a high powered zoom camera in one
location, find the one that suits your needs and plug it onto the system.
What about pan tilt and zoom cameras? Pan tilt and zoom cameras are fine if you
are sitting at the screen and controlling the camera. At other times you can almost
bet that whatever it was that you needed to see was in the opposite direction from
the view of the camera. PTZ cameras are generally much more expensive than
regular cameras and for the cost of a PTZ you can purchase 4 regular cameras
and be constantly looking in all directions at the same time.
I could go on and on but let's change subject here and talk about the camera lens.
Some cameras come with a fixed lens that can not be changed, others have
interchangeable lens'. Again, you usually get what you pay for. An expensive lens
will be made with a high quality glass, an inexpensive lens will be made from poor
quality plastic. Some lens' are fixed, some have zoom capabilities. I generally like
to use a camera with a zoom lens, not manipulated from the operators location but
adjustable at the camera. This gives us more flexibility when mounting because
we can zoom the picture in and out to frame it as desired. Once we are suited with
the picture, the lens is locked down. For general coverage a 2.9 mm lens gives a
wide angle view just short of the fish eye effect. Most parking lots can be viewed
fine with a lens between 2.9 and 8.0 mm.
An now lux. the lux figure is simply the ability of the camera to see in low light
conditions and lower is better. A black and white camera will normally have a
lower lux rating than a color camera, meaning that it can see better in low light.
Infrared cameras can see in total darkness because the infrared LED's act as a
flashlight for the camera to see. Infrared cameras normally provide a color picture
during daylight and a black and white picture when the infrared's are turned on.
If you have further questions about cameras, feel free to contact us.