Webcams are not unique in their ability to freeze the atmospheric turbulence. For many years before the webcam, low-light video and security cameras where used to freeze the seeing, with the added advantage that data can be stored on videotape. In 2005, this data can be stored on a variety of tape formats and on DVD as well. Indeed, the two technologies are now merging, as domestic video recorders featuring terabyte hard disks are now on the market. This book is about lunar and planetary webcam imaging, but I think I would be wrong to leave out video options altogether. One never knows when the technology trend will swing back the other way and some observers are far happier using video or camcorder type equipment, especially on bright objects or when timing events like an asteroid occultation where a time marker is easily superimposed on the recording.
One video option for the planetary imager is the KC381 camera produced by the Italian company Astromeccanica, run by the keen planetary imager Paolo Lazzarotti. Using the most sensitive interline CCD in the Sony ICX range, the ICX409AL, the KC381 (Figure 6.4) is a potent camera, but the pixels are slightly nonsquare at 6.5 x 6.3 microns. Again, while this is easily corrected in software, some astro-imagers are put off by sampling with nonsquare pixels. The KC381 is a monochrome camera so color filters will be required to construct a color image.
One videocamera that has been proven to perform on bright astronomical targets is the Neptune 100, manufactured by the Japanese company Watec. Priced at around $650, the Neptune 100 is a videocamera sensitive to 0.001 lux and with a spectral sensitivity from the visual band through to the near infrared at 940 nm. For solar imaging, or imaging of Mercury, Venus, and the Moon, it is a good choice for those who prefer to save 1/60th second video frames rather than fill their hard disk. Of course, a set of color filters will be needed too.
Another option is the Lumenera Lu070 (pcb) and Lu075 (enclosed) range of USB 2.0 VGA cameras (Figure 6.5). Lumenera is a company based in Ottawa,
Ontario, in Canada. Their 070/075 range currently comprises four models (color, monochrome, and enclosed or modular versions of each) that can convey uncompressed, 8 or 10 bit, 640 x 480 pixel frames at 60 frames per second down a 480 Mbit/second USB 2.0 line. (Say goodbye to your hard disk space!) No frame grabber is required with this system. The video images just come straight down the USB cable. Again, like the Neptune 100, this is an especially excellent option for bright objects where exposures of 1/60th second are long enough. The Lumenera
cameras store their video images onto hard disk using the SEQ video file format. Software can easily convert this into AVI format (for Registax) at a rate of about 1000 frames per minute. According to tests carried out by Damian Peach, there is little difference between the 8- and 10-bit imaging modes, and the SEQ 8-bit files are about 25-30% smaller than an equivalent AVI file. A great feature that the Lumenera Streampix software has is that you can pause the AVI capture at any time, meaning that if a cloud passes over the object you can pause the video recording. In tests carried out by Damian using a monochrome Lumenera LU075 camera while observing Jupiter from Barbados, he concluded that it easily outperformed even his (USB 1.1) ATiK 1HS. The Lu075 could easily work at 18 to 34 frames per second and give acceptable, smooth results, where the ATiK was happier at 5 or 10 frames per second. One thing to bear in mind is that the Lumenera does have 7.4 micron pixels (c.f. 5.6 micron in the ToUcam/ATiK) so focal lengths have to be increased by 32% to deliver the same sampling resolution with respect to the smaller pixel webcams. In addition, please note that these excellent cameras start at just under $1,000, so are considerably more expensive than webcams or modified webcams.
Adirondack Video Astronomy (AVA) is one of the best and most innovative astronomy dealers in the U.S., and it is not surprising that they stock a comprehensive range of the latest CCD and webcam-based products (such as the ATiK range). Their website at http://www.astrovid.com is well worth checking out whether you live in the U.S. or elsewhere. AVA offer a couple of in-house products called Astrovid Color Planetcams that can be used for planetary imaging. While these tiny (190 gram) video cameras do not offer huge benefits over their rivals, they do have a number of features that may appeal to the beginner. Firstly, they feature small, 4.2 micron, pixels. For a beginner, video-filming the Moon at, say, 0.4 arc-seconds per pixel, a focal length of only two meters will be required. So a 20-cm f/10 SCT will fit the bill without any Barlow lens or Powermate being required. A simple 2 x Barlow will give all the resolution a beginner would want even on a night of steady seeing. These cameras also feature a rather unusual negative image feature enabling the planet to be viewed on the monitor as a "live" color negative when trying to bring out details in bright regions. The advanced model of the Astrovid Color PlanetCam, titled the "Computer Controlled EEPROM" version, can have its settings (gain, gamma, sharpening, color balance, exposure) controlled remotely from a PC and the settings can be stored for each planet imaged. This is a useful feature e.g., for live planetarium/observatory imaging of the planets. However, despite these unique features, the planetary imaging enthusiast will probably greatly prefer the webcam approach, as stacking hundreds of images to create the smoothest image is his or her aim and not live video imaging sessions in front of an audience.
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