…continuedNight! Camera! Action!
After your first videotaping session, fatigued muscles will probably make you wish for another way to keep a camcorder at the eyepiece. Try mounting the camcorder on an ordinary camera tripod. With small equatorially mounted refractors and compound telescopes like Schmidt-Cassegrains and Maksutov-Cassegrains, the movement of the eyepiece as the telescope tracks the sky's motion will be modest relative to a stationary tripod-mounted camcorder.
Supporting the camcorder on a separate tripod is more difficult with larger refractors and Newtonian reflectors because their eyepieces move more as these telescopes pivot. You'll be forced to reposition the camcorder and its tripod frequently, so it's better to attach the camcorder to the telescope and let it go along for the ride. Brackets for this purpose can be purchased from astronomy retailers or fashioned from wood, plastic, or aluminum.
Once you devise a way to attach your camcorder to your telescope, one additional challenge will remain. Despite remarkable advances in miniaturization, a camcorder's videotape mechanism, viewfinder, and battery can weigh several pounds, so you'll need to counterbalance that extra weight carefully. Many amateurs have found a handy solution at their local sporting-goods store in the form of jogger's ankle weights, which can be attached to a telescope using strips of Velcro.
Supporting your camcorder on a tripod or coupling it directly to your telescope will also let you use the remote controls that come with many camcorders. These accessories are a real boon because they let you adjust the camcorder's zoom lens and exposure settings without touching the camera and jiggling the highly magnified image.
To make prints of scenes from your videotapes, you might imagine that simply employing the camcorder's freeze-frame mode while playing back the video on your TV will show a nice image, and perhaps you can take a photograph of your TV screen. Unfortunately, if you're using an analog camera (VHS or Hi8 formats) this will only teach you some harsh lessons about the effects of electronic noise and the physiology of human vision.
When a videotape is played back, 30 discrete images (usually called frames) are displayed every second. Your eye and brain integrate them as a seamless view. At a rate of 30 frames per second, phenomenon called flicker fusion causes the sequence to appear continuous. Your eye-brain combination fills in between the frames and also averages the noise (snow) of individual frames, creating the perception of a vivid moving picture. But in the freeze-frame mode of analog video, the display will invariably suffer from a poor signal-to-noise ratio and have a grainy salt-and-pepper look reminiscent of an overenlarged photograph. To add insult to injury, successive frames will almost invariably exhibit a phenomenon called image excursion small, erratic displacements caused by atmospheric turbulence. When examined frame by frame, a videotape of a planet that appears stationary and well-defined in the "play" mode will reveal contortions reminiscent of an amoeba under a microscope.
Using a DV-format camcorder avoids some of these problems, because digitally captured video images don't suffer from the "blurry" effects of analog recording. Nevertheless, you’re still at the mercy of our unstable atmosphere. To smooth out the noise and incrementally displaced images, it's necessary to combine dozens or even hundreds of the sharpest frames,a process called "stacking." This was a very laborious, time-consuming task before the advent of software capable of automatically detecting the best frames and precisely superimposing them to create a composite image.
Of course, to use these programs, you must first get the video onto your computer. There are several ways to accomplish this, thanks largely to the prevalence of software to edit home videos and burn DVDs. Many video cameras now come equipped with ports and cables that will send video output to a computer's USB or FireWire input. The movie-making software will then capture the video and save it in a file format for video editing, usually AVI or QuickTime.
If you have an older analog camera, you can install a television card in your computer. These cards have TV tuners that allow you to watch broadcasts on your computer monitor (and sometimes record them to disk). Many also feature inputs to connect VCRs or other video sources, allowing analog signals to be converted to digital video. While intended for people to turn their home videos into DVDs, you can use it to import your astro video and run it through image-stacking software.
The result of stacking will be a single picture that you can save to your computer. Then make a copy on your printer or at a local photo-service center to show your family and friends just how good a planetary imager you are!
A valuable book that delves into the digital details of astrovideography is the recently updated Video Astronomy by Steve Massey, Thomas A. Dobbins, and Eric J. Douglass ($24.95 from Sky Publishing), which further illustrates the techniques in this article and much more.
Camcorder-to-telescope adapter brackets are available from:
LensPlus 11969 Livonia Lane Redding, CA 96003 530-549-4257 www.lensadapter.com
Orion Telescope & Binoculars P.O. Box 1815 Santa Cruz, CA 95061 800-447-1001 or 831-763-7000 www.oriontelescopes.com
As with any realm of consumer electronics, the equipment, tools, and techniques change quickly. Join the VideoAstro e-mail discussion group to remain up to date with the latest trends in video imaging. The site offers valuable infor-mation on video equipment and techniques as well as an excellent gallery of amateur video images.