First Targets

The Moon is the biggest and brightest object in the night sky. Odds are that it was the first object you looked at through your telescope, and it's the best subject for learning the ropes of video astronomy. After you've honed your skills videotaping the Moon for a night or two, you'll be ready to try your luck with the planets. The waxing and waning phases of Venus, the seasonal advance and retreat of the polar caps of Mars, the ever-changing features of Jupiter's cloud belts and four bright Galilean moons, and Saturn's magnificent ring system are all within the grasp of your backyard telescope and a camcorder.

Combined with typical amateur telescopes, even the most affordable camcorders are capable of capturing dramatic lunar sequences. Examples include the spires of shadows cast by mountains towering above plains of frozen lava and the rims of craters flashing into view as they catch the first rays of the morning Sun.

Set up your telescope on an evening when the Moon is between the crescent and gibbous phases, so that deep shadows throw lunar topography into bold relief near the Moon's day-night terminator. Select a low-power eyepiece (the one with the largest number printed on it), point your telescope at the Moon, and bring the image into focus.

Now manually set the focus of your camcorder's lens to the infinity position. If your camcorder has an autofocus feature, turn it off; otherwise it may continue to hunt for focus while you stand there exasperated. Carefully bring your camcorder up to the eyepiece of the telescope, taking pains to center its lens directly over the eyepiece while keeping it parallel to the emerging beam of light. To avoid jarring the telescope, don't let the camcorder touch the eyepiece. A small gap between the camcorder's lens and the eyepiece will not affect the image.

If the image in the camcorder's viewfinder appears slightly out of focus, tweak the telescope's focusing knob until the lunar landscape snaps into crisp view. Depending on your telescope's eyepiece and the camcorder's lens, the viewfinder may show a diffuse, dark circle surrounding the brightly illuminated lunar image. Since you'll want the image to fill the frame, adjust the zoom setting of the camcorder's lens until this effect — called vignetting — disappears. The zoom lens also provides a very convenient way to increase magnification without changing eyepieces.

If your camcorder is equipped with a digital zoom, don't use it. This dubious "feature" actually creates a lower-resolution picture because the camera uses fewer picture elements (pixels) of the CCD to fill the field. Used in conjunction with an eyepiece of moderately long focal length (15 to 25 mm), the optical zoom of most camcorders will provide plenty of magnification for afocal imaging.

The more you enlarge the image, the dimmer it will become, so experiment with the camcorder's zoom and exposure controls until you achieve an acceptable compromise between magnification and image brightness. Technically speaking, dim images have a poor (or low) signal-to-noise ratio that gives them an objectionably grainy appearance — a look appropriately called "snow." The definition and sharpness of your video recordings will not be determined solely by the optical quality of your telescope and the steadiness of the atmosphere. Older VHS or 8-mm camcorders record only 240 to 250 lines of horizontal video resolution. The S-VHS and Hi8 formats represent a marked improvement of 400 to 420 lines of resolution, while today’s popular digital video (DV) approaches 500 lines. High-definition (HD) cameras have 1,080 lines.

Another way to get a view of the heavens onto video is to use special electronic eyepieces in which the lens you would normally look through has been replaced with a silcon chip. Meade Instrument’s Electronic Eyepiece ($70) features 320-by-240-pixel, black-and-white video that is fed through a cable directly to the video input of a TV or video recorder. The camera is powered by an internal 9-volt battery and is available from Meade retailers.

Barska makes a similar eyepiece that captures a 640-by-480-pixel color image and sends the signal through a cable that plugs into your computer via a USB connection, which also powers the eyepiece. The Digi-Eyepiece ($65) comes with Windows software to display, edit, and save the movies.

Used in conjunction with a TV, these products are great for showing groups of people the Moon and planets. But with limited ways to change exposure settings manually, they aren’t as capable as other video recorders.