Questions bout CCTV
1-What's the difference
between Hardware Compression and Software Compression?
Hardware Compression: Both
Capturing Video Signal and Compressing Video Signal are done by DSP chipset
integrated on DVR Board. It doesn't need the computer's CPU to do this work.
It's low cost of CPU and RAM resources. In this system the computer CPU's task
focus on answering network request, streaming the video/audio to network and
saving recorded data to local hard disk.
Software Compression: The
DVR Board only capture video signal but doesn't compress it, it is the computer
CPU and RAM to do this compression work. It's high cost of CPU and RAM
resources. In this system the computer CPU and RAM are often overloaded. It is
easier to crash than hardware compression system.
2- How do I choose the
correct camera for my application?
This in general is a
comparatively difficult decision. Many aspects of the installation must be taken
into consideration in order to obtain the correct performance that meets your
A high-resolution camera
should be considered where greater detail of scene is required. E.g. Color 460
TVL, Monochrome 570 TVL. Choosing a more sensitive camera will improve
reproduction in poorly lit areas. The sensitivity of a camera is indicated by
the minimum amount of light in order for the camera to produce a usable picture.
e.g. Color 1.0 Lux at F1.2.
A conventional camera
produces a pale backdrop when an object is shot against a bright background. BLC
(Back Light Compensation) will counter strong light sources retaining picture
Concentrated light sources
directed towards the camera (e.g. car head lamps) can be inverted by an optional
peak white inverter or an eclipser function. This has the effect of bringing
detail to areas and making an object clear, that would otherwise be shadowed.
3- How do I set up a camera
and lens for use in Low Light conditions and or with Infra Red Lighting?
When setting the back focus
of a Color camera for low light conditions you should place an ND1 (Neutral
Density) filter in front of the lens. When setting the back focus of a Mono
camera for low light conditions you should place an ND3 (Neutral Density) filter
in front of the lens. When setting the back focus of a Mono camera fitted with
I/R lighting for low light conditions you should place an IRP (Infra- Red Pass)
filter in front of the lens.
4-Should you not have any of
the above filters you may have to attend site during the hours of darkness.
I have installed a new
camera and lens why I am unable to obtain a sharp image?
The most common resolve to
this is to ensure that both camera and lens are the same mount i.e. 'CS' mount
lens on a 'CS' mount camera and a 'C' mount lens on a 'C' camera.
What are OSD cameras?
(On Screen Display)
cameras have a menu system within the camera assembly that can be accessed in
order to set functions such as Iris levels, AGC on/off and most features of
standard and advanced cameras.
5- Why do I have a clear
sharp picture during the day and it is out of focus at night?
This is due to the depth of
field changing as the light conditions change and can be easily overcome by
following set procedures.
6-When can I use a manual
A general rule of thumb is
only to use a MI lens in an internal application. This is because you are
reliant on the electronic circuitry of the camera compensating for light changes
in the scene and this is not able to compensate to the same degree as that of an
Auto Iris lens.
7- How do I back focus a
camera fitted with a fixed focal length lens?
This is achieved by
following five simple steps.
Set the physical focus of
the lens to infinity (clockwise from the front).
Aim the camera at the
subject to be viewed.
Release the camera back
Adjust the back focus to
obtain the best possible picture.
Secure the cameras back
8- Can I fit a 1/3"e; Lens to
a 1/2"e; camera?
The simple answer is NO.
9- How do I connect an Auto
Iris lens to a camera?
This is usually performed by
a simple plug-in connection to the rear or side of the camera. However you
should always refer to the relevant camera handbook.
10- What is the difference
between Auto Iris and Direct Drive Lenses?
An Auto Iris lens is one
that automatically adjusts its iris for changes in the scene lighting levels.
The motor that opens and closes the iris is driven by an Amplifier that
processes a small electronic signal changing with the light level.
A Direct Drive 'DD' lens
does not have this Amplifier and can only operate with a camera fitted with one.
A camera specification will
indicate the available output options.
11- Does the 'f' stop
matter when choosing a lens?
Yes, lenses are usually
specified as having a minimum and maximum 'f' stop rating; the 'f' stop is a
measure of how efficiently the lens allows light from the scene, to pass through
the lens and onto the camera CCD sensor. The maximum aperture (when the lens is
fully open), is the minimum 'f' stop number and the minimum aperture, (just
before the lens completely closes) is the maximum 'f' stop number.
A low minimum 'f' stop
number means that the lens can pass more light through during dark conditions,
which will produce better pictures at night.
A high maximum 'f' stop
number may be necessary where there is a high level of light or reflection. This
will prevent the camera ‘whiting out’.
12- How do I Back Focus a
camera fitted with a ZOOM Lens?
This can be achieved by
following these steps.
Set the lens to full wide
Set the physical focus of
the lens to infinity (clockwise viewed from the front).
Aim the camera at an object
at least 30 Meters away.
Release the camera back
Adjust the back focus to
obtain optimum clarity.
Zoom the lens in to full
telephoto and focus on a nearby object.
Keep this object in view as
you slowly zoom out and if all is set correctly it should remain in focus
Secure the back focus
13- How do I set up an Auto
An Auto Iris lens has two
'pots' on the side commonly marked ALC (Automatic level control) and LEVEL.
The ALC control has settings
of PEAK and AVERAGE (P+A).
The LEVEL control has HIGH
and LOW settings 'H+L'.
The adjustment allows
control over any bright areas in the scene e.g. sun reflection through windows,
street lighting etc. There are two settings PEAK and AVERAGE.
If set to PEAK, bright areas
in the scene are taken into account more, reducing the contrast in the
surrounding area. This allows more detail to be seen in the bright areas.
If set to AVERAGE the lens
takes the bright areas less into account which usually causes over brightness or
flare in these areas, but raising the contrast of the surrounding area.
The only correct way to set
the VIDEO LEVEL is by the use of an oscilloscope, for most Engineers this is not
A more practical method is
to use a service test monitor and a camera that you know has been set up
correctly to 1 volt peak to peak.
Put the video output from
this tested camera into the test monitor and adjust the contrast and brightness
until you are satisfied with the picture. Mark the contrast and brightness
controls so that you can set them to this position again.
Set up each camera adjusting
the ALC (as above) then adjusting the LEVEL to obtain a picture similar to that
achieved with the test camera. (Making sure that your test monitor is set to
your marked positions)
NB: On most zoom lenses the
ALC adjustment is a speed control for the Iris motor and is best left in the mid
position. The Amplifiers on Auto Iris lenses are sensitive; so adjust the LEVEL
and ALC with a proper trimming tool instead of an ordinary screwdriver, which
can induce small voltages.
14- What size monitor should
I be using?
The correct size monitor is
dependent on its use e.g. the number of images to be displayed at any given
time, the viewing distance and the available space.
15-What is Video
This is the end of line
resistance of any CCTV system and this should be set to 75 ohm. Should you
encounter any double image or ghosting this is more often than not caused by two
pieces of equipment in series both having the 75-ohm switch set on. Only the
last piece of equipment should be set at 75-ohm.
16- What camera housing
should I use and at what IP Rating?
Camera housings come in
various shapes and sizes. With regard to the correct IP rating protection, this
will range from dust and water ingress. This system is governed by a number of
European and British standards.
Protected against dust -
low-pressure jets of water from all directions - limited ingress permitted.
Protection against low
pressure jets of water from all directions - limited ingress
17- What is the difference
between simplex and duplex multiplexers?
Video multiplexers are
designed to allow recording of several cameras onto one recorder.
A simplex machine is best
suited to applications where recording only is the priority. Simplex machines
cannot display multi screen images (i.e. quad, 9 way and 16 way split) while in
the record mode.
If an operator is monitoring
the system (i.e. security guard) then a duplex machine is more suitable. A
duplex machine can provide screen splits and user selectable images without
affecting what is recorded onto the recorder. Should you use two recorders, it
becomes possible to record and playback simultaneously.
18- Which pan and tilt unit
should I use?
The choice is wide and
varied dependent on the system requirements. You may require Top mount, Side
mount, 230V AC or 24V DC to name just a few.
Pro: Can fit two IR lamps on
the side of the Pan/Tilt. These act as a counter balance enabling you to use a
lighter duty Pan/Tilt head.
Pro: Compact size.
Con: Restricted tilt often
-45 to 0 dependent on the housing fitted.
Con: Cannot be inverted.
Pro: Can be inverted.
Pro: Often cheaper.
Pro: Large tilt often +or-
Con: Difficult to mount IR
Con: Generally large size.
19- What type of
illumination can I use with color cameras?
Only lighting within the
visible wavelength should be used with color cameras. Tungsten Halogen is often
the recommended source of lighting.
20- Can I use I/R Lamps with
The answer to this is a
definitive NO. Color cameras are typically fitted with an IR cut filter and will
not allow IR light in excess of 700Nm to pass resulting in the camera performing
poorly in these circumstances.
21- Do I have to use a
Regulated Power Supply?
In general the answer is
yes. Most manufacturers will recommend the use of such power supplies as
standard with their equipment. You should always consult the manufacturer’s
specifications prior to the connection of any power supply.
22-What is the maximum
distance I can run 12vdc when powering a camera?
This is a commonly asked
question and there is no simple answer. Some manufacturers may recommend that
their cameras can be run over (X) distance with (Y) cable. This however should
still be considered as a general guide. Cable conductor size and installation
route must also be taken into consideration. If you are unsure, we would
recommend that you contact Technical Support for guidance.
23-What is Digital CCTV?
Digital CCTV, or Digital
Closed Circuit Television, is the technology used in modern surveillance
systems. Traditional ,VCR, CCTV pictures are sent via cctv cameras to a closed
area, e.g. a CCTV Monitor, this type of CCTV is likely to produce lower
resolution images and have to be displayed via cabling in the workplace. Modern
Digital CCTV Systems can be operated remotely via a pc or mobile phone, can
monitor various locations and can be monitored from wherever there is internet
or GPRS Access.
A History of CCTV Systems
The saving of CCTV footage
has changed in the last 5 years. The industry move has been away from analogue
to Digital CCTV Systems:
In the past, all CCTV
Cameras were attached to a Multiplexor (A device that will split multiple camera
pictures onto an individual CCTV Monitor). The Multiplexor then sends the
analogue camera images to a Time Lapse Video Player. These are special CCTV
recording devices that can record up to 960 hours of footage on a three hour
Video Cassette. This method is still used today for simple CCTV installations
but the quality of recording is usually very low (1 Frame Per 12.8 Seconds).
Currently the majority of
CCTV systems use Digital technology. Digital CCTV Surveillance uses current PC
technology to digitize the CCTV camera images and compress them into a PC
friendly format. These digital images can then be stored on a PC's Hard Disk
Drive. As the digital cctv images are stored on computers Hard Drives it is
possible to save digital cctv footages and access them speedily and easily.
Digital CCTV also has the advantage over Analogue CCTV systems that the image is
of a far higher resolution.
There are two types of
Digital Surveillance Systems:
Digital Video Recorders
A Digital CCTV Video
Recorders, (DVR), are stand-alone units that are capable of saving digital CCTV
images to a PC. DVR look similar to a standard Video Cassette Recorders (VCR's).
CCTV Cameras are connected
to the back of the unit via standard CCTV Camera connection referred to as BNC.
By connecting a CCTV Monitor or standard Television to the DVR you are able to
view your CCTV Cameras in different screen divisions (single camera, 2x2, 3x3
etc) and also playback footage at the touch of a button.
Some DVRs can have built in
Motion Detection Technology. This means that digital footage is only recorded
when someone or something walks in front of your CCTV Camera.
It is also possible with
some DVRs to view your cameras remotely via an ADSL (Asymmetric Digital
PC Based Digital Video
Surveillance Capture Cards
PC Based Digital CCTV
Surveillance systems are a reasonably new technology in the CCTV Industry. This
type of Digital CCTV system works in two stages. You then install the digital
cctv surveillance card and software on to your PC. This Software (or program)
will allow you to view your Digital CCTV Cameras, search through previously
recorded footage, backup footage to CD/DVD, control PTZ Cameras either on the PC
system or remotely and much more.
Cameras are attached to the
back of the Geovision PCI Card using the standard BNC connection used in all
come in a variety of formats depending on 1) The amount of cameras required
2) The Frame Rate per Second
(FPS) Quality required (16 FPS - 400 FPS)
Frame Rate is important, as
the higher the Frame Rate, the higher the quality of recording and the more Real
Time your cctv recording will be.
Real Time Recording for 1
camera is 25 Frames Per Second (PAL). In order to capture 16 cameras in Real
Time, you would need:
25 FPS x 16 Cameras = 400
Frames Per Second PCI Surveillance Card
How to choose a CCTV Camera?
Choosing the correct CCTV
Camera for your digital surveillance system is very important. The Digital CCTV
Camera, together with a CCTV Lens, uses a CCD (Charge Coupled Device) sensor
that captures the image and turns it into a signal that is sent to the monitor
or surveillance system.
You will need to decide the
following when choosing a cctv camera & lens for a digital cctv system:
The Digital Camera Location:
Will the camera be situated Indoors / Outdoors
The amount or variance of
light conditions for the digital cctv camera: Will the camera have to record in
low-light conditions such as at night?
The Field of View required
for the camera: How wide or narrow an angle of vision is required
The Focal Length - How far
away objects you wish to record will be from the camera
24- What is a ground loop?
An AC current that can be
produced in a cable. This is usually caused by parts of the system being fed
from different electrical sources resulting in different earth potentials at
each end. The result is interference on the signal, usually in the form of dark
bands across the monitor and on occasion tearing in the top third of the image.
25- How can I eliminate
ground loop faults?
This can be achieved in a
number of ways, the easiest of which is the installation of a Ground Loop
Isolation Transformer. This is best installed at the monitor or recording end of
26- What is the correct
level for a video picture?
The correct level is 1 volt
peak to peak. This can only be accurately set either with an oscilloscope or
with a video level meter.
27-Manual or Auto Iris
The iris is the part of the
lens that determines how much light falls upon the camera CCD sensor.
The Manual Iris 'MI' lens
has this fixed at the time of installation. As the light levels change in the
scene, the lens can do nothing to prevent either too little or too much light
entering the camera. Virtually all cameras employ an Automatic Electronic
Shutter 'AES' to compensate for these variations when fitted with an MI lens.
However they are only able to cope with a relatively small change in light
An MI lens should never be
used in an external situation, as the camera will be unable to cope with large
changes in light levels. Use an Auto Iris ‘AI’ lens in this case, or where large
scene illumination changes take place.
The advent of new sensor
technology such as PIXIM may result in a change to this situation in the future