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What's the difference between Hardware
Compression and Software Compression? |
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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. |
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How do I choose the correct camera for
my application? |
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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
requirements.
A high-resolution camera shuld 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.
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How do I set up a camera and lens for
use in Low Light conditions and or with Infra Red Lighting?
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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. |
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I have installed a new camera and lens
why am I 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. |
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What are OSD cameras? |
| 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. |
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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. |
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When can I use a manual iris lens? |
| 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. |
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How do I back focus a camera fitted with
a fixed focal length lens? |
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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.
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Can I fit a 1/3" Lens to a 1/2"
camera? |
| The simple answer is NO. |
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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. |
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What is the difference between Auto Iris
and Direct Drive Lenses? |
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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.
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Does the ¡®f¡¯ stop matter when choosing
a lens? |
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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¡¯.
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How do I Back Focus a camera fitted with
a ZOOM Lens? |
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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 Meters 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.
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How do I set up an Auto Iris lens? |
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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.
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What size monitor should I be using?
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| 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. |
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What is Video Termination? |
| 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. |
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What camera housing should I use and
at what IP Rating? |
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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 ¨C limited ingress permitted.
IP65
- Protection agaist dust - no ingress.
- Protection against low pressure jets of water from all
directions ¨C limited ingress
ermitted
- Protection against high pressure water from all directions
- limited ingress permitted.
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What is the difference between simplex
and duplex multiplexers? |
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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.
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Which pan and tilt unit should I use?
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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.
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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. |
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Can I use I/R Lamps with color cameras?
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| 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. |
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Do I have to use a Regulated Power Supply?
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| 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. |
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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. |
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What is the difference between RG59 and
URM70 Coax? |
| 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 center conductor
and is more suited to installations such as PTZ cameras. |
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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. |
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How can I eliminate ground loop faults?
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| 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. |
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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. |
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Manual or Auto Iris Lens? |
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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.
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