Info on digital video recorders
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Most digital video recorders will record on to some kind of memory card, be it SD (secure digital) or CF (compact flash). The good news is these cards are getting cheaper and with bigger capacities. Other devices might use a hard disk to record video on to. These are usually less expensive (price vs quality) and they will hold more video but you need to be sure you can isolate them from the vibration. Wind buffeting, exhaust/HT electro magnetic interference can also cause a hard disk recorder some problems. If you're looking to mount your recorder on your bike under the seat etc...then you should probably consider a solid state recorder that uses a memory card with no moving parts.
Another thing to consider is storage space vs quality. As compression codecs continually improve, we can store more high quality video using less storage space. The resolution, compression method, frames per second and bitrate of a digital recorder will determine the quality of the video and how much of it you can fit on your card. The first most important thing is frame rate, for smooth video you need 25fps and no less. 30fps is an american NTSC standard. We use 25fps here in Europe. The compression method dictates how effciently the video quality is maintained vs the amount of space per second of video. Mpeg4 is becoming a standard for this with compression levels reaching DVD quality in the more expensive recorders. Bitrate is how much information is being stored per second. Generally the higher the bitrate the better but as compression methods get more sophisticated the bitrate can come down but quality is maintained. A higher bitrate means your memory card will be filled quicker. When looking for a digital recorder, the bitrate and compression algorithms are not usually listed in the adverising spec. Just because a particular recorder has a resolution of 640 x 480 does not mean you will get DVD quality!
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CMOS
Basically there are two types of camera. Cmos (complementary metal oxide semiconductor) cameras are the least expensive to manufacture because of the relative simplicity of their sensor pick-ups. The measurement of image quality largely depends on the resolution of the camera. Resolution is measured in horizontal tv lines. There are just over 600 lines of horizontal resolution on a PAL television. The higher the resolution of the camera (more horizontal lines) the more defined the final image will appear. Cmos cameras tend to be slightly smaller then CCD cameras.
Currently, cmos cameras go upto 380 tv lines. You 're talking about an image quality comparable to that of a cam-corder of a few years ago, the ones that used to take full sized vhs tapes? Now when you consider the size of these tiny cmos cameras next to the size of our latter day shoulder riding friends it's pretty amazing.
We quite often use a cmos camera in some obscure (high risk) position as a second camera using a simple video switcher to change to the camera we want the shot from.
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CCD
The other type of camera is a CCD camera (charge coupled device). CCD cameras have much more complicated circuitry to produce a sharper image and a more realistic reproduction of colours. The best CCD "bullet" style cameras available at the moment can display up to 480 lines PAL which is a nice sharp clear image, in reality, any camera of this size displaying upwards of 420 lines will give you good picture quality.
CCD "bullet" cameras allow more light to the sensor with bigger internal lenses which makes the final image camparable to a mid-range cam-corder.
For the DogCam we chose a Sony camera 480 tv lines, it has excellent pick-up with a 3.5mm lens for the best light spread. The DogCam is a class CCD colour camera in a hard water-proofed casing. A treated outer lens specified by ourselves lets only the preferred light spectrum in reducing glare and minimising over exposure.
Our latest camera, the DogCam Pro 550 zoom is the best camera to use if you are looking to make high quality DVD resolution videos. 550 lines is the optimum resolution for recording on to a camcorder. This camera has been designed by DogCamSport and includes some very clever image processing allowing it to change it's settings automatically to suit your filming environment. This camera is recommended for filming in the snow where over exposure would bring a lesser helmet cam to it's knees.
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Over Exposure
Is what you get when too much light gets to the camera sensor, like opening your eyes to a bright light first thing in the morning. Any camera will over expose if you point it at the ground and then quickly towards the sun. It's about how long the camera takes to adjust that determines a quality of the unit. Cmos cameras have the most difficulty in adjusting quickly to fast changing light conditions. CCD cameras handle this much better.
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