Planetary Cameras

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It's possible to use a cooled, integrating "deep sky" CCDcamera like an SBIG or a Starlight Xpress to image the planets. Some amateurs, like Houston's Ed Grafton, have produced impressive Solar System pictures that way, but, surprisingly, a $100 webcam will almost always best a $3,000 CCD camera on planetary subjects. What's needed for high resolution planetary pictures is not big CCD chips. Small chips with small pixels are just right. "Project" a large image onto a chip with small pixels, and extremely fine details can be registered. Long exposures are not needed, either. Usually 1/30-second is more than enough. Because exposures are this short, it's not necessary to cool the CCD chip to reduce noise. "One shot color" is nice too: all currently available webcams are color devices. Most astronomical CCD cameras require users to take and combine three filtered black-and-white shots to produce one color picture. By the time the last exposure is done, Jupiter's fast-rotating disk may have caused details to smear out in the final combined color image. "Small chips," "small pixels," "one-shot color." These add up to great planetary images.

You can spend a thousand dollars or more on a camera specifically designed for planetary imaging, like the Lumenera SkyNx, but that's not necessary in the beginning. Start with something cheap, learn the game with that, and then think about investing big bucks if planetary imaging becomes an enduring interest. The traditional place to start has been with an off-the-shelf webcam. One of these little devices, designed for video teleconferencing, connects to a PC via a USB port and sends its streams of digital video directly to the hard drive without need for tapes or DVDs.

Where to get a webcam? There are plenty on the shelves at Walmart, but the webcams there probably will not be optimum for astronomy. Most of them use CMOS rather than CCD chips as their imaging sensors, which makes them less sensitive to light. One of these CMOS cams can do a fine job on the Moon and is a way to get going at minimal cost, but there's a better solution, the Phillips Toucam. This tiny camera has been popular with amateurs for years and is still available as the Phillips SPC900NC. It features a 1/4-inch CCD chip with small (5.6 micron) pixels, is impressively sensitive, and delivers good color. These things, combined with a price of about $125, make it a natural for beginning imagers. Phillips cameras can be difficult to find at U.S. electronics discounters but are easily available from astronomy dealers, most notably Adirondack Video Astronomy.

What does it take to get an off-the-shelf webcamready for the telescope? First, some kind of an adapter is needed to allow it to be inserted into a 1.25-inch focuser or Barlow. A plastic 35mm film canister duct-taped onto the camera will work, but a more attractive and durable factory-made "nosepiece" is desirable. Adirondack sells these as does an Australian company, Mogg, which sells worldwide (Appendix 1). To use these adapters, the lens of the webcam is removed and the adapter screwed on in its place. Don't worry about having to remove the lens; it's useless for planetary imaging. "Barlow projection" (see below) is the path to high-resolution planetary images.

One other desirable accessory is an Infrared (IR) blocking filter.. Webcam chips are very sensitive to IR, and unless it's kept out the color balance of the camera will be badly skewed into the red. It's possible to fix the color of a strongly pink Jupiter or Saturn in post-processing, but even then color will usually be better in filtered shots than in unfiltered ones. An IR filter can improve sharpness in refractors (which may not be color corrected for IR), but CATs are not affected by this problem. Some webcams contain built-in IR filters, but an add-on like the Baader IR block filter (a 1.25-inch filter that screws onto the webcam adapter or Barlow) usually provides noticeably better results. If possible, a webcam's built-in IR filter—usually a tiny film chip—should be removed, since it will typically be of poor quality.

Choosing a planetary camera used to be easy: you bought a webcam and that was that. Today, there are more choices. Astronomy-ready webcam-like devices are available from both Meade and Celestron (Plate 70) and have the advantage of being ready-to-go out of the box. A 1.25-inch adapter is built in, the astronomy-oriented software needed to control the camera and process images is in the box, and there are instructions sufficient to help get a novice started in webcam astronomy.

Meade's entry, the LPI($100), is nicely priced and its 1/3-inch chip is substantially larger than the average 1/4-inch webcam sensor. That makes it possible to take in wider vistas of the Moon, focal length for focal length, and makes it easier to get a planet in the frame at high magnification. The camera ships with Meade's innovative Envisage software that can not only take images but can do a large part of image processing on the fly. Despite these good things, we don't recommend the LPI except for the Moon. Although the chip is larger than the average webcam CCD chip, it's a less sensitive CMOS device. Also, its relatively large (8 micron) pixels tend to blur detail. Do use an LPI on the Moon, however, where it does an admirable job.

The best inexpensive "astronomy webcam" is probably Celestron's NexImage ($100). The company isn't overly informative about the parentage of the camera, but it appears to be a repackaged Toucam or something similar. It definitely uses the same CCDchip as the Phillips camera and is capable of producing images identical to those from the Toucam. The NexImage package includes a 1.25-inch adapter and a CD containing image capture and processing software. Like the Toucam, the NexImage can benefit from an IR blocking filter (Celestron sells one for the camera).

Plate 70. (Webcams) Webcams and webcam like imagers can shoot everything from the Moon to the most distant galaxies. L - r: Celestron NexImage, Meade Deep Space Imager (DSI), Meade Lunar and Planetary Imager (LPI). Credit: Author.

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