It interests me when the geek rejects tech he doesn't fully understand --- but his grandparents adopted as soon as it became available for their light trucks and RVs.
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.
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.
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.
Wide Angle Field of View
The field of view provided by any camera is determined by a combination of image sensor 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.
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.
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.
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).