Can
I use any type of cctv camera outside?
Not
really. Some mini-cameras are designed for outside use with waterproof
cases ( e.g. bullet cameras ) but if you need lenses of different focal
lengths and especially if you need auto-iris lenses ( which are best
for outside because of varying light conditions ) then mini-cams won't
be satisfactory. Normally, body cameras
are used outside but need to be mounted inside a special
outside housing.
These housings are rainproof and can also contain a heater unit for
really cold climates and/or a fan for hot climates.
Mini-dome
cameras, and similar, meant for inside use only, should not be used
outside.
Why
are color cctv cameras better than Black and White (B/W), even though
B/W cameras will work at lower light levels?
Traditionally,
B/W cameras were considerably less expensive than color cameras, much
more light sensitive and often of higher resolution. Today, most of
these things are not true. The price gap has narrowed considerably,
resolutions are basically the same and while B/W cameras can still be
more light sensitive than color cameras, the light levels at which our
color cameras will still produce images is as low as 0.3 Lux, which
is pretty low light ( now, Starlight color cameras which utilize frame
integration, will provide color pictures in as little as 0.003 Lux ).
Taking these points in mind, when you add the far more positive recognition
qualities of color images, it makes color cameras, in general, a better
buy today than B/W cameras.
Why
don't I need 30 frames per second video recording on all cameras?
Video
surveillance systems are generally intended to allow the image capturing
of intruders and crime perpetrators. The purpose of these systems is
not to make movie quality videos. Recording rates of as low as 1 or
2 frames per second will catch virtually any criminal act. Even at these
frame rates, with many cameras all recording on motion, the compressed
video files produced are multi-Gigabytes per day. Imagine what the file
sizes would be if cameras were all recording at 30 frames per second!
Of course, recording frame rates must be fast enough so as not to miss
anything - a major problem with multi-camera time-lapse VCR systems.
Sometimes time lapsing on VCR systems can be as great as 1 frame very
5 or 6 seconds, in order to get the number of hours of recording time
high enough. This kind of recording frame rate can certainly miss many
things, but a digital system recording at anywhere from 1 to 6 frames
per second should miss nothing and still provide many days of recording
capacity.
What
does an auto-iris lens do for me?
Outdoor
cameras or cameras indoors facing a window or an outside door will have
varying light conditions. CCTV display and recording systems are set
to a certain level of image brightness and contrast. When light levels
change in the images produced by the cameras, the displayed and recorded
images will either be too bright and washed out or too dark and non-resolvable.
The only way to solve this is to use an auto-iris lens. These lenses
have an electric motor-driven iris which is opened or closed according
to signals fed to it from the camera. Once set, a camera equipped with
auto-iris drive will attempt to produce a video signal of constant brightness
by opening or closing the auto-iris of the lens, as light levels change.
If
I purchase fixed focal length lenses or cameras with fixed lenses, can
I exchange those if I don't like the field of view that I see?
Yes
you can, provided they are shipped back in the original packaging and
are in "as new" condition. However, you will be liable for
the shipping charges, both ways and this, combined with the hassle involved,
usually makes it an unsatisfactory thing to do. Better, in the first
instance, if you are unsure about the lens focal length required, to
purchase cameras with vari-focal lenses. These are manually adjustable
over a range of focal lengths, most commonly from 3.5 to 10.5mm, to
give a wide range of field of view.
How
far from the computer can I place cameras?
Using
RG59 Coaxial Cable, each cctv camera can be placed up to 600 feet from
the computer and up to 1,000 feet with RG6 Coax.
Can
I use wireless transmission from cameras to computer instead of cables?
A
qualified yes. Basically it depends on the range, frequency and type
of the transmitter/receiver units, the conditions under which they are
to be used and the number of units you want to use. Most transmitter/receivers
today are 2.4GHz units. This high frequency has the advantage of longer
range per power unit but only in clear line of sight. 2.4GHz signals
do not travel through objects (walls, trees etc.) very well. Low power,
low range 2.4 GHz transmitters are cheap but usually produce very poor
image quality. Until recently, higher power units were very expensive
( approaching $1,000 per pair). Today there are some higher output 2.4Ghz
transmitter/receiver units available ( see our
cctv accessories
page ) at more reasonable prices. Our units have four selectable operating
frequency channels so up to four pairs of transmitter/receivers can
be used in one system. For longer transmission distances, though, even
with long range high power units, it is important to have as clear a
line of sight as possible between the transmitter and the receiver.
Can
I use my old cameras mixed with new ones?
Yes, providing
certain conditions are met. Even with the same color type, some older
cameras and some newer cameras mixed together can cause problems because
of very different image synchronizing systems. In this event, you can
get interference between one camera image and another. Color cameras
are more prone to this type of problem. Today's GV products and
Sentry DVRs will handle a combination of color and B/W cameras.
How
many days/weeks of recording can I store?
This
depends on how big is your hard drive, how many cameras are you using
and under what conditions are you recording ( on motion, on alarm, continuously,
etc. ) and whether you are using MPEG4 or wavelet recording. Assuming
that you are recording only when motion is present ( the most common
recording method today ) using a 30fps board and assuming that you have
4 cctv cameras and that there is movement in the surveilled area for
16 hours a day, 5 days a week, and you are recording at 320x240 pixel
resolution with MPEG4 compression, you could expect to use up about
20 to 25GB of disk space per week. So, a 40GB drive would hold about
2 weeks of recordings under those conditions.
Of course,
if you record at 640x480 pixel resolution, as you can with the GV products,
and/or you are using a 120fps board, the disk space used will increase.
Because of the way that MPEG4 compresses video, there is not a definite
mathematical formula that can be applied to say exactly by how much
the recordings would grow.
Since
hard drives are now relatively inexpensive, it pays to use as big a
capacity drive as possible ( and/or multiple drives) if you are concerned
with storing many weeks of recordings before overwriting.
What
happens when my hard disk is full?
Normally
the system will begin to overwrite the recorded image files, oldest
first. You can choose for recording to cascade from one drive to another
( i.e if the "C" drive is full, the system can begin to write
on the "D" drive), if you have more than one hard drive.
