|
How do I choose the correct
camera for my application?
Back to
top
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 customer s
requirements.
A high resolution camera should be considered where greater
detail of scene is required. E.g. Colour 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. Colour 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 quality.
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.
How do I set up a camera and
lens for use in Low Light conditions and or with Infra Red
Lighting?
Back to
top
The answer to this is the same as that for questions relating to
Back Focusing on Page 31 and 34, with the addition of the
following:
When setting the back focus of a Colour 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.
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 am I unable to obtain a sharp image?
Back to
top
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. If in doubt please refer to our
lens diagram on page 32 of the CCTV catalogue.
What are OSD
cameras?
Back to
top
OSD (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.
Why do I have a clear sharp
picture during the day and it is out of focus at
night?
Back to
top
This is due to the depth of field changing as the light
conditions change and can be easily overcome by following our
answers on page 31.
When can I use a manual iris
lens?
Back to
top
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.
How do I back focus a camera
fitted with a fixed focal length lens?
Back to
top
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 focus mechanism.
- Adjust the back focus to obtain the best possible picture.
- Secure the cameras back focus mechanism.
Can I fit a 1/3" Lens to a
1/2" camera?
Back to
top
The simple answer is NO. For further details refer to our Field
of View Calculator on page 30.
How do I connect an Auto Iris lens to
a camera?
Back to
top
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.
What is the difference
between Auto Iris and Direct Drive Lenses?
Back to
top
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.
Does the f stop matter when
choosing a lens?
Back to
top
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 .
How do I Back Focus a camera
fitted with a ZOOM Lens?
Back to
top
This can be achieved by following these steps.
- Set the lens to full wide angle view.
- Set the physical focus of the lens to infinity (clockwise
viewed from the front).
- Aim the camera at an object at least 30 Metres away.
- Release the camera back focus mechanism.
- 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 (track).
- Secure the back focus mechanism.
How do I set up an Auto Iris
lens?
Back to
top
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 .
ALC
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.
LEVEL
The only correct way to set the VIDEO LEVEL is by the use of an
oscilloscope, for most Engineers this is not an option.
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.
What size monitor should I
be using?
Back to
top
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. Please see the table opposite for your
guidance.
What is Video
Termination?
Back to
top
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.
What camera housing should I
use and at what IP Rating?
Back to
top
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.
IP55
- Protected against dust - limited ingress.
- Protection against low pressure jets of water from all
directions limited ingress permitted.
IP65
- Protection against dust - no ingress.
- Protection against low pressure jets of water from all
directions limited ingress permitted
- Protection against high pressure water from all directions -
limited ingress permitted.
What is the difference
between simplex and duplex multiplexers?
Back to
top
Video multiplexers are designed to allow recording of several
cameras onto one recorder.
Simplex
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.
Duplex
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.
What is the difference
between Standard VHS and SVHS recordings?
Back to
top
In general the main difference apart from cost is the increase
in overall resolution. A standard VHS machine may achieve in the
region of 300 TVL (mono) whereas S-VHS machines may achieve in the
region of 400 TVL. However this being achieved will depend on the
correct ancillary equipment being used.
Which pan and tilt unit
should I use?
Back to
top
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.
TOP MOUNT
- 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.
SIDE MOUNT
- Pro: Can be inverted.
- Pro: Often cheaper.
- Pro: Large tilt often +or- 180
- Con: Difficult to mount IR lamps.
- Con: Generally large size.
What type of illumination
can I use with colour cameras?
Back to
top
Only lighting within the visible wavelength should be used with
colour cameras. Tungsten Halogen is often the recommended source of
lighting.
Can I use I/R Lamps with
colour cameras?
Back to
top
The answer to this is a definitive NO. Colour 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.
What is an ISDN Telephone
Line?
Back to
top
An ISDN (Integrated Services Digital Network) Line is a digital
system allowing a camera to be updated at a rate of 15 frames a
second.
What is a PSTN Telephone
Line?
Back to
top
A PSTN (Public Switched Telephone Network) Line is an analogue
network allowing a camera image to be updated every few seconds and
is therefore slower than that of an ISDN network.
What is an ADSL
Line?
Back to
top
Also known as Broadband, an ADSL (Asymmetric Digital Subscriber
Loop) line is a form of Digital Subscriber Line in which the
bandwidth available for downstream connection is significantly
larger than for upstream. Although designed to minimise the effect
of crosstalk between the upstream and downstream channels this
setup is well suited for web browsing and client-server
applications as well as for some emerging applications such as
video on demand.
What is a Leased
Line?
Back to
top
Leased Line, sometimes known as Kilostream, Megastream or
Private wire. This is NOT a dial up line but is connected 24hrs a
day and is usually subject to an installation charge and a
quarterly bill.
What is full picture
update?
Back to
top
Full picture update is a technology that enables a transmission
system to update a high quality full picture refresh at very fast
speeds.
Do I have to use a Regulated
Power Supply?
Back to
top
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 manufacturers specifications prior to
the connection of any power supply.
What is the maximum distance
I can run 12vdc when powering a camera?
Back to
top
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.
What is the difference
between RG59 and URM70 Coax?
Back to
top
In general there is little difference. However RG59 is a hard
drawn conductor and is best suited to fixed camera installations.
URM70 has a multi stranded centre conductor and is more suited to
installations such as PTZ cameras.
What is a ground
loop?
Back to
top
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.
How can I eliminate ground
loop faults?
Back to
top
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 the system.
What is the correct level
for a video picture?
Back to
top
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.
How often should I replace
my video tapes?
Back to
top
In general it is recommended that all video tapes should be
replaced after a period, no greater than 20 passes of each tape.
That being 10 record and 10 play back. This will also be dependent
on the quality of tape being used and that the recording equipment
is in good operational condition.
Manual or Auto Iris
Lens?
Back to
top
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 levels.
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 indeed anywhere 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.
How often should I replace
my IR Lamp Bulb?
Back to
top
Installers and end users are often disappointed by the life they
get from Halogen bulbs.
Manufactures quote life expectancy figures as 'Mean Time'. They
are not a guarantee of the bulb life. This simply means that on
average after a number of hours quoted by the manufacturer HALF OF
THE BULBS WILL HAVE FAILED. If the 'Mean Time' of 4,000 hours is
quoted, half the bulbs will fail within that 4,000 hour period
(5.5months).
Matters appear worse during the period of October to March,
obviously because of the longer hours of darkness. During this
period, lamps may be on as much as 16 hours each day. A simple
calculation may be used in order to provide adequate maintenance on
these systems.
If you have 5 external cameras each with 2 lamps that gives us a
total daily lamp usage of:
10x16hr = 160 hours per day.
If the lamp has a mean life expectancy of 4,000 hours, this
means that you can expect a bulb to fail every:
4,000/160 = 25 days.
You should make sufficient provision for this within a
maintenance contract. | 
