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). The better multiple camera systems can automatically switch more than one camera.
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.
If a system doesn't specifically list this feature, then it almost certainly doesn't have this feature. Never even consider purchasing a rear view camera system that doesn't have this feature.
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 120 degree field of view is strongly 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 and produce a 120 degree field of view --- that is ideal for most applications.
On the other hand, there are some rear view systems advertised with fields of view as wide as 210 degrees. 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 limited number of high quality rear view cameras are designed with 170 to 180 degree field of view lenses.
I can't emphasize strongly enough that you should never use a cheap camera that provides a 'fish-eye' view --- you will eventually back into or over something or someone!
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.
Given the option, you should always select a rear view camera system that utilizes a high quality CCD image sensor from a well known manufacturer. Sharp and Sony CCD image sensors are the best available. If the system you're considering purchasing doesn't state that it utilizes a "CCD" image sensor, then it almost certainly doesn't.
Weather Resistant 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.
Weather resistant 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 weather resistant --- 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 other manufacturers), or for connecting other video and/or audio devices.
Never purchase a rear view camera system that utilizes RCA type connectors for exterior connections. These connectors are not designed for exposure to the elements, and they will eventually fail. Beware of sellers who claim that their inferior RCA connectors designed strictly for interior use are superior to screw together weather resistant connectors. Think about this and decide for yourself.
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 LEDs (light emitting diodes) come in.
On a high quality night vision equipped camera, the infrared LEDs 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 LEDs operate at a light frequency that is well beyond 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 cameras will typically illuminate out to a distance of 30 to 50 feet from the camera.
While the number of infrared LEDs may or may not be important (just as with light bulbs, various infrared LEDs provide 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.
Never consider purchasing a rear view camera system that does not include infrared night vision illumination. The infrared night vision illuminators should provide a minimum of 10 feet of illumination, and 20 to 30 feet or more of illumination is strongly recommended.
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 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. All modern 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", 7" and 9" (measured diagonally) screen sizes. Of the available LCD type monitors, the TFT-LCD (thin film transistor - liquid crystal display) is the best, and 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 'green screen' monitor is more comfortable to view in low light, and produces an image that makes it easier to discern variations in shades of color, especially at night.
The LCD type monitors are significantly thinner 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 (not recommended), hung in place of or over 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. In some cases smaller displays (2.5" to 4" diagonal measurement) may be desirable for use within the limited space inside smaller passenger vehicles.
Types of Cameras
There are four common types of cameras used for rear view camera systems. These are 'surface', 'flush', 'license' and 'side' mount type cameras. Each type of camera has its own specific advantages and disadvantages. 'Dual' surface mount (two cameras in one mount) are also available.
Most larger vehicles are best suited to the 'surface' mount camera, which can be attached to any flat (or near flat) surface. These cameras are the type most often observed mounted high on the rear of a vehicle, aimed down at approximately 30 to 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, buses, and all commercial vehicles.
On many passenger vehicles, pick-up trucks, and sport utility vehicles, the 'flush' mount 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.
The 'license' mount cameras attach to the existing license plate mounting screws, so no new holes are required to attach the camera to the vehicle. Depending upon the location of the license plate, this may or may not be a good solution for your vehicle.
The 'side' mount cameras are intended for viewing the area along the sides of the vehicle. They may also be installed on the roof, ceiling or walls for use with other various observation needs.For some applications, a 'forward facing' camera is desirable. These are most often used to see ahead of the front bumper, or inside a passenger or cargo carrying compartment in which observation using a camera facing toward the front is required.
All cameras should include infrared night vision. While one-way audio is available on many of the 'surface' mount cameras, and may be useful for an assistant to help with backing larger vehicles, I'm not aware of any 'flush', 'license' or 'side' mount cameras that include audio capability.
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.One serious consideration should be that most of the wireless systems sold (on eBay and elsewhere) are total and complete garbage. Most wireless systems have directional antennas on the camera and receiver that must be aimed directly at each other, and those antennas are easily broken during normal use.
Although I sell the highest quality wireless rear view camera systems available anywhere, I personally STRONGLY 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, and at least some occasional interference. Check the specifications of any wireless system you are considering purchasing very carefully, and if you decide to buy a wireless system, buy the best wireless system available!
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