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 to some degree. HD cameras can allow you to blow up a
picture and read a tag number across the parking lot. How big of a parking lot
depends upon the resolution of the HD camera. Currently CCTV cameras typically
range from 2 to 8 megapixils in resolution.
So why don't we just use all HD? Now a days we pretty much do, the cost
of high definition cameras and related equipment has decreased so much recently
that you can buy an HD camera now for the same price an analog camera was selling
for just a couple of years ago. Looking at HD cameras, you'll need to decide
how you want to connect the camera to the recording unit. You have two choices,
either coax or cat5. Cat5 cable is much cheaper than coax however the cat5
based cameras and equipment typically cost 25% or so more than the coax based
equipment. While we have installed both types of systems, we have installed
more coax based systems. Besides being less expensive, the coax based systems
offer an important advantage to our existing customers. The new coax HD
recording units will work with either an analog or HD camera. So if a customer
wants a better picture of the driveway or maybe the cash register, then all
they have to purchase is a new recording unit and one camera, the recorder will
work with all their other existing cameras. As one of the analog cameras dies
from old age, the customer can replace it with an HD. Currently the highest
resolution that we can offer over coax is 5 megapixils. HD over cat5 can go as
high as 8 megapixils and 8 megapixils will give you a 4K ultra quality picture.
All of 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 are
multiple formats. While some formats have gone the way of the dodo bird,
there are still at least three in regular use. We typically use a TVI format,
and some cameras will do multiple formats. 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 advice, avoid purchasing a boxed system with cameras that use
a molex plug that carries both power, video, and sometimes 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 2.8 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 2.8 and 12.0 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.