Most home camcorders are not sensitive enough to pick up images of nebulas and galaxies. For such distant objects, astro-imagers have turned to specialized CCD cameras. CCD stands for charge-coupled device, a type of light-sensitive chip similar to the chips used in home camcorders.
Instead of movies, CCD cameras record single long exposures. During an exposure, light falls onto an array of pixels arranged in a grid pattern on the chip. At the end of the exposure, each pixel reads out a voltage that corresponds to how much light fell onto it. The readings are digitized (turned into binary numbers consisting of Os and Is), then sent to a computer that can re-create the image on its monitor.
CCD cameras have major advantages over conventional film. A CCD image is digital data, which can be manipulated, stored on computer disks, and even transmitted via modem. You can also see the results immediately at the telescope. Most importantly, CCDs are much more sensitive than film, requiring exposures of only 5 minutes to record what might take a fast film 30 to 60 minutes to pick up. With these shorter exposures, there is often no need for elaborate guiding. Because the images are digital, they can be enhanced on a computer, making it possible to discover faint objects even in light-polluted or moonlit skies.
The main drawback is the expense of a CCD camera— which can cost as much as a good telescope—and also the hardware and software that goes along with it: you will need a personal computer loaded with plenty of RAM, space on the hard drive, and image-processing programs. You may also want a laptop computer so you can easily operate the camera in the field.