EVERYTHING YOU NEED TO KNOW ABOUT REAR VIEW CAMERAS
by:
interceptinc
Automatic System Switching
Possibly the most important feature to look for when purchasing a rear
view camera system, is that system's ability to switch on automatically
whenever the vehicle's transmission is placed in reverse. This is
accomplished by connecting a single wire to the vehicle's backup light
circuit, sending a signal to the rear view camera system, causing it to
switch on without any action by the operator.
Many so-called 'rear view camera systems' don't have this feature, and
will require you to manually switch the system on every time you want to
see behind you. The higher end systems (any true 'rear view camera
system') will have this ability to switch on automatically, in addition to
being turned on manually any time using the monitor's front panel power
button (or wireless remote control, if so equipped).
Since it's very inconvenient and extremely unsafe for the motor
vehicle operator to be required to switch the system on manually every
time he or she wants to back up, it's imperative that you never purchase a
rear view camera system without the ability to switch on automatically. If
the system you're considering doesn't clearly list this feature, it almost
certainly doesn't have this feature. Never purchase a rear view camera
system without this feature.
Mirror Image Capability
A rear view camera system should have the capability to produce a
'mirror' (or 'reverse') image through the camera and/or monitor. Many of
the systems sold (especially those on eBay) don't have this capability. It
doesn't matter whether the camera produces a 'mirror' image, or the
monitor reverses the image left to right, or as on some high end systems,
both the camera and monitor can switch between 'normal' and 'mirror'
images.
Why do you want a 'mirror' image? In order to see the same type of
image that you would see in a rear view mirror, the camera and/or monitor
must be capable of reversing the image produced. This capability will
provide the same type of image through a rear view camera system that you
would see if you were looking into a rear view mirror, and that's exactly
what you want for safe operation. Many high end systems not only allow you
to select between a 'normal' and 'mirror' image, but also permit you to
'flip' the picture vertically for additional camera mounting options.
Wide Angle Field of View
The field of view provided by any camera is determined by a combination
of image sensor (see "CCD vs. CMOS Image Sensor" below) size and lens
focal length. The larger the image sensor, the wider the possible field of
view. However, a larger image sensor does not necessarily guarantee a
wider field of view. Many rear view camera systems utilize a 1/4" image
sensor, and provide only a 60 to 90 degree field of view. While a 90
degree field of view may be sufficient for some smaller vehicles, a 110 to
120 degree field of view is preferred. You should absolutely avoid any
system that produces lower than a 90 degree field of view. Most high
quality rear view cameras that utilize a 1/3" image sensor produce a 110
to 120 degree field of view --- that is ideal for most applications.
On the other hand, there are some rear view systems advertised with
150, 160, 180 or even 210 degree fields of view. These super wide field of
view cameras are not intended for use on rear view camera systems, and
will generally produce a 'fish-eye' image that will be extremely distorted
and very dangerous to use as part of a rear view camera system. A few very
rare specialized rear view cameras are designed with 150 or 160 degree
fields of view, but these are specialty units and are very expensive (not
generally available for everyday use).
CCD vs. CMOS Image Sensor
The two types of image sensors that are available for rear view
(backup) camera systems are the CCD ("charge coupled device") and CMOS
("complementary metal oxide semiconductor"). The type of image sensor that
your rear view camera system uses will be the most important factor in
determining picture quality. Besides the overall resolution, a camera that
utilizes a CCD image sensor will provide significantly better images under
very low and very bright lighting conditions.
All except the lowest quality consumer digital photographic and video
products utilize CCD image sensors. All professional digital photographic
and video equipment utilize CCD image sensors. Although there are some
reasonably high quality CMOS image sensors, no CMOS image sensor will
deliver the quality image that a CCD image sensor will provide. Many lower
priced (and some more expensive) systems use the less expensive and
inferior CMOS image sensor.
Weatherproof Camera, Cables & Connectors
Remember, a camera mounted on the exterior of a motor vehicle will be
subjected to more than just water. Such a camera may be exposed to a wide
variety of elements, including water, snow, ice, salt, road grime, oil,
dust, detergents, and high pressure washes. Just as the camera can be
exposed to these elements, so are the exterior cables and connectors.
Weatherproof cables and connectors should also be used for all exterior
installations. Many systems sold (particularly on eBay) utilize RCA type
connectors for exterior connections. Stay away from these systems, as RCA
connectors (the same type of connectors found on most televisions and
VCR's) are not weatherproof --- they should never be used for exterior
connections.
Exterior connections should always be made by weatherproof connectors
--- weatherproof connectors screw together, so they can't accidentally
come unplugged. This is especially useful when using a rear view camera
system with a trailer and tow vehicle combination.
Many systems include interior RCA connections. These interior
connections are not subject to any of the elements found on the exterior
of a motor vehicle, and are perfectly acceptable. In fact, these interior
RCA connections can be useful for adding additional cameras (even those
from another manufacturer), or for connecting other video and/or audio
devices.
Infrared Night Vision
This is probably one of the least understood features available, and
yet, it is one of the most important features. Although a high quality
camera (especially a high quality CCD camera) can provide a picture under
a wide variety of lighting conditions (including very low light), it can't
provide a clear picture in near or total darkness. That's where the
infrared night vision illumination LED's (light emitting diodes) come in.
On a high quality night vision equipped camera, the infrared LED's turn
on automatically whenever the ambient (background) light drops to a level
that's too low for the image sensor to produce a high quality picture. The
infrared LED's operate at a light frequency that is well above the human
eye's ability to see, but the image sensor in the camera is designed to
detect this light just like the visible light that we can see.
The primary difference between visible and infrared light is seen when
using a color rear view camera system. On a monochrome (often referred to
as "black and white") rear view camera system, there is little difference
seen in the image. However, since infrared light doesn't produce colors
that are visible to the human eye, all color systems will produce a
monochromatic image at night.
One big difference between a high quality rear view camera and a lower
quality one, is its ability to illuminate the area seen by the camera.
Ideally, the infrared illuminators will illuminate the entire field of
view produced by the camera, and will illuminate out to a distance of at
least 20 feet from the camera. The higher end systems will typically
illuminate out to a distance of 30 to 50 feet from the camera.
While the number of infrared LED's may or may not be important (just as
with light bulbs, various infrared LED's have higher or lower light
intensities), the total light output and the camera's sensitivity to
infrared light, will determine the overall performance of the camera's
night vision capabilities. Some sellers will make ridiculously exaggerated
night vision claims (no on-board infrared illuminators will extend beyond
approximately 50 feet), and these claims should be ignored as nothing more
than sales hype.
Automotive Power Source
One of the most serious questions for most users of these systems,
isn't whether or not the system they purchase will work with their vehicle
--- it's how well and how long will it work with their vehicle? Many of
the lower quality systems (including many sold on eBay) do not include any
type of voltage regulator or filtering circuit. The lack of such a circuit
will cause the constant varying voltage produced by the vehicle's
electrical system to either damage the system, or at a minimum, produce
serious variations in picture quality.
If the system you're considering doesn't specifically state that it
has a voltage regulator or filter, then it probably doesn't.
Nearly all rear view camera systems will work on any vehicle that
operates from 12 volts DC --- that's nearly every late model car, pickup
truck, sport utility vehicle, recreational vehicle, and trailer. However,
there are exceptions to this rule, including some specialty vehicles, as
well as many commercial and military vehicles. Some rear view camera
systems are capable of operating at a variety of voltages, usually either
12 to 24 volts DC, or 12 to 32 volts DC.
Some rear view camera systems include optional voltage regulators that
can be added for use on those vehicles that operate from the higher
voltages (usually 24 or 32 volts DC). This option is necessary if you plan
to install the system on a vehicle that operates from one of these higher
operating voltages.
Audio Monitoring
Audio capability can be helpful when the driver needs the assistance of
a helper while backing. While you may or may not require audio, it can
also be useful when a camera is being used to monitor the interior of a
trailer (carrying people or animals). While some systems include audio,
others do not. If the description does not specifically state that audio
is included, chances are it's not.
The only disadvantage to audio is that in order for the microphone
within the camera to receive sound from outside the camera housing, there
needs to be a small hole leading to the outside world. While the higher
quality cameras with audio are designed to keep water out during normal
use, there is a possibility that high pressure spray from a car wash (or
other source) could possibly enter the camera housing.
Most of the higher quality rear view cameras that have audio house the
microphone within a sealed compartment that is separate from that which
houses the camera and/or locate the microphone hole on the back side of
the camera (the side that faces toward the vehicle), to prevent water from
being forced into the microphone hole.
Types of Monitors
Although there are several sizes, a wide variety of quality, and many
different features, there are essentially two different types of monitors
available --- these are CRT (cathode ray tube --- commonly referred to as
a "picture tube") and LCD (liquid crystal display) monitors. Most (if not
all) color rear view camera systems will use an LCD type monitor. Most (if
not all) monochrome (black and white) rear view camera systems will use a
CRT type monitor.
The LCD monitors are most commonly available in 5" to 5.7" (measured
diagonally) and 7" to 7.2" (measured diagonally) screen sizes. These are
sometimes referred to by their generic screen sizes, as just 5 or 7 inch,
leaving off the decimal point. Of the available LCD type monitors, the TFT-LCD
(thin film transistor - liquid crystal display) is significantly better
than the LCD type. If the seller does not clearly specify that the monitor
is the TFT-LCD type, chances are it's not.
When selecting a rear view system that uses an LCD type monitor,
always choose the TFT-LCD type monitor for the best picture under the wide
variety of lighting conditions encountered while operating a motor
vehicle.
The CRT type monitors found with most monochrome rear view camera
systems come in two basic types --- 'gray screen' (resembles an old 'black
and white' television screen) or 'green screen' (the monitor actually
produces a picture with a green hue). Neither of these have any
overwhelming advantages or disadvantages, although some people do have a
preference. The idea behind the 'green screen' monitor is that the color
green is easier on the eyes in darkness, and as with military night vision
equipment, produces an image that makes it easier to discern variations in
shades of color, especially at night.
The LCD type monitors are significantly smaller and lighter than the
CRT type monitors, making it easier to mount them in smaller vehicles. The
larger CRT type monitors must usually be mounted on top of the dashboard,
the transmission hump, hung from overhead, or occasionally mounted into
the dashboard. The smaller LCD type monitors can be mounted in any of
these locations, as well as on the face of the dashboard, on the sun
visor, hung in place of the rear view mirror, or many other locations
(depending upon the specific vehicle).
In most cases you should avoid those rear view systems that use a
monitor with less 5" diagonal measurement, as they do not provide adequate
detail for safe backing of larger vehicles. Any system that has a monitor
with less than a 5" diagonal measurement should only be considered for use
as a rear view or backup camera system on a car or other smaller passenger
vehicle, and NEVER on a larger type vehicle.
Types of Cameras
There are two common types of cameras used for rear view camera
systems. These are the 'surface' (or 'standard') mount and the 'flush' (or
'keyhole') type cameras. Each type of camera has its own specific
advantages and disadvantages, and each is designed for a specific type of
use.
Most larger vehicles are best suited to the surface mount camera, which
can be attached to any flat (or near flat) surface (and most other
surfaces utilizing a variety of mounting options and brackets). These
cameras are the type most often observed mounted high on the rear of a
vehicle, aimed down at approximately 45 degrees. This mounting position
provides a commanding view of the area behind the vehicle, and because of
the downward angle, provides excellent depth perception. This type of
camera is by far the best choice for larger vehicles, including
recreational vehicles, trailers, busses, and all commercial vehicles.
On many passenger vehicles, pick-up trucks, and sport utility vehicles,
the 'flush' (or 'keyhole') type camera is the preferred choice. This type
of camera mounts through a hole in the body of the vehicle, and provides a
view that is more or less directly level with the road surface (the better
'flush' mount cameras include rings that permit slight angling of the
camera). While this type of camera does not provide the degree of depth
perception provided by the 'surface' mount camera (because it can't be
angled down to the same degree), it is well suited to passenger vehicles
and provides a much cleaner and unobtrusive installation, since the only
part of the camera that is visible is the lens cover and bezel.
Both types of cameras are available with infrared night vision
capabilities, although availability varies from one system to another. In
most cases, the night vision capability of 'flush' mount cameras will
provide less illumination distance than an equal quality 'surface' mount
camera (this is due to the limited number of infrared LED's that can be
positioned within the 'flush' mount camera housing). While audio is
available on many of the 'surface' mount cameras, I'm not aware of any
'flush' mount cameras that include audio.
Wired vs. Wireless
While the picture produced by a high quality wireless system may be
okay when the vehicle is stationary, every wireless device (every one!) is
susceptible to interference, and that interference will be worse when the
vehicle is in motion. Because a wireless system transmits a video image
through the air, instead of via a cable, there can be some interference
from a variety of sources, including electrical interference, high power
radio and television transmitters, and many other sources encountered as
the vehicle moves.
Think of the difference in quality between the images produced by an
old television antenna on the roof, versus a modern cable television
signal. The mere fact that the video image must be converted to a radio
signal, transmitted through the air, and converted from a radio signal
back to a video image at the receiver and monitor, means that the
possibility for signal degradation is a serious consideration.
One serious consideration should be that most of the wireless systems
sold (on eBay and elsewhere) are total and complete garbage. Most don't
provide the 'mirror' image (see "Mirror Image Capability" above). Most are
not weatherproof. Most have directional antennas on the camera and
receiver that must be aimed directly at each other. Most have antennas
that are easily broken during normal use.
I personally prefer a wired system. If you absolutely insist upon a
wireless rear view system, then you will have to settle for a lower
quality picture than you would have with a high quality wired system.
Check the specifications of any wireless system you are considering
purchasing very carefully, and buy the best wireless system available!
