Want to see more through your telescope than you can with an eyepiece? You could try your hand at imaging with a DSLR or CCD camera, but that’s got a long, steep learning curve. If you don’t have years to master this craft, there’s an alternative: video astronomy. Astronomical video cameras give real-time, full-color views of deep-sky objects with an amazingly high sensitivity that effectively triples the aperture of a small telescope, even in highly light-polluted skies. And these cameras provide an analog signal you can view with an off-the-shelf television or video monitor. Over the next few articles, we take a look at deep-sky video astronomy and see if it’s something that might make sense for you…
Video astronomy got started perhaps 10 to 15 years ago when a handful of amateur astronomers learned how to attach simple and inexpensive computer webcams or early handheld video cameras to a telescope. These early homemade cameras only worked with bright objects like the Moon and planets, but they enabled astronomers to capture a live image to a computer or TV and wow the crowds at public outreach events.
More ambitious stargazers developed custom software to collect thousands of images of the Moon or planets from a webcam and telescope in just a few seconds, throw out the fuzzy images caused by bad seeing, and combine (or “stack”) the best images into very sharp renderings that rivaled images from large professional telescopes. This sort of “webcam astronomy” has matured, and the big astronomy vendors now sell commercial versions of these lunar/planetary cameras packaged with software and ready to go out of the box. Practiced imagers can capture spectacular images with these cameras, but they’re still not sensitive enough for deep-sky objects.
Things got more interesting when, over the past decade, Asian semiconductor manufacturers developed highly sensitive CCD chips for low-light security and surveillance cameras. Some skilled and enterprising amateur astronomers packaged these CCDs with sophisticated control, cooling, amplification, and processing electronics to create the first true astronomical video cameras that give full-color views of the Moon and planets, and also faint deep-sky objects like nebulae, galaxies, and star clusters. With a sensitive commercial astronomical video camera mounted in the eyepiece holder of a small telescope, it’s possible to snap an image like the one below in a few seconds:
As you can see, the color and detail visible in a 6” telescope far exceeds what you can see visually, and the image comes right out of the camera. The image above, for example, required no guiding or post-processing: the camera did all the work. The term “video astronomy” is accurate because the camera provides a standard analog video signal that can be viewed with a video monitor or TV. For bright objects like the Moon, the image is updated every 1/500 to 1/30 of a second depending on observing conditions, so you really do see a real-time view of the object through your telescope.
Fainter objects make the camera work a little harder, and each video frame gets updated over several seconds to minutes. Which is fine, since these objects don’t change much in this time frame. So with each update, you get a sort of electronically-assisted “snapshot” that enables real-time observation of faint objects through a telescope that are not otherwise accessible. As a rule of thumb, you can see objects 2-3 magnitudes fainter with a video camera than you can see visually. Which means you’re effectively tripling the size of your telescope aperture without having to buy, use, and store a much larger telescope. It’s darned impressive.
These cameras are a delight in dark skies, but with the right light-pollution filter, astronomical video cameras also give extremely good views in light polluted skies and can easily reveal objects that you can’t see at all visually through the eyepiece. For example, even in the most transparent sky, I can’t see the “Spindle Galaxy”, NGC 4565, from my urban backyard with a 102 mm refractor… and I’ve tried for years, and the background sky is too bright. But here’s an image of the galaxy taken in 30 seconds with an astronomical video camera and light-pollution filter, and with no post-processing:
Alas, there are a few trade offs. The sensors in these cameras are quite small, about ½” on each side, which is typical for analog video. This does give a somewhat restricted field of view in a telescope. And the pixels in the sensor are relatively large, which is why they’re intrinsically sensitive to low levels of light. Big pixels in a small sensor mean these cameras have low resolution, typically 640×480 or 720×480. That’s still high enough to render a pleasing image, but it’s far lower than the many megapixels available with the DSLR’s or large CCDs used by the experts to capture the detailed images you see in Sky and Telescope or APOD.
If you’re intrigued by the possibilities of video astronomy, look for the next article in this series. It will take you through the basics of how these little cameras are used in a small telescope…