Find the USB Port and Buy a Webcam

The first step on your webcam journey is to check that you have a PC with a USB port. If your computer was made before 1998 it may not have one, in which case there is not much point proceeding. A USB port looks like a small slot in the PC and is completely different in appearance from the multi-pin serial and parallel ports. In addition, if your PC's operating system is earlier than Windows '98 then USB will not be supported. PCs and operating systems prior to 1998 simply will not work with USB webcams. Do not worry if the PC does not have high-speed USB 2.0; the basic USB is fine.

If you do have a modern PC with a USB port, great, you can proceed with buying a webcam. The best cheap webcam for lunar and planetary imaging, at the time of writing, is the Philips ToUcam Pro (Figure 7.1). It is very sensitive to light (the sensor is a true CCD, not a CMOS chip) and that is why it is so good. The 2005 model is called the Philips ToUcam Pro II PCVC 840K and will work with Microsoft Windows 98, 2000, ME, and XP. Of course, technology moves on all of the time and by the time this book is published the ToUcam Pro may not be the best on the market. It is a good idea to check on the Internet and see what the top planetary imagers appear to be using at any one time. Proper CCD-based webcams had far superior performance to noisier CMOS versions when this book went to press.

I ordered both my ToUcam Pros online, from Amazon. At the time of writing, the ToUcam Pro II was priced at around $100. Electronically, the original, white, egg-shaped ToUcam Pro I and the new, silver, ToUcam Pro II are identical.

The webcam, as purchased, will not fit onto your telescope, so you also need to purchase an adaptor. One end of this adaptor must be about 31.5 mm in diameter (to fit into the 31.7-mm [1.25-inch] diameter hole of astronomical telescopes and accessories): the other end needs to be much smaller and threaded to fit the tiny thread which the supplied webcam lens screws into. Fortunately there are many suppliers of 31.7 mm to webcam thread adaptors, many of whom advertise in the popular astronomy magazines like Sky & Telescope. In fact, the ToUcam Pro is so popular that you can buy one with an adaptor included, as a complete package, from many astronomy suppliers. A third (optional) accessory is a so-called UV-IR

Figure 7.1. The Philips ToUcam Pro II with the supplied lens removed. The tiny CCD chip can just be seen. Image: Martin Mobberley.

blocking filter to give a more natural color response, but this is certainly not essential for first-time users. The Celestron NexImage planetary imager is simply a ToUcam Pro's electronics in a moulded telescope-compatible casing, complete with bundled software.

The other thing to think about at this stage is how to enlarge the image of a planet falling onto the CCD chip. A good starting point is to increase the telescope's focal ratio until it is at least f/20, in other words, the focal length is 20 times the telescope's aperture. With an f/10 Schmidt-Cassegrain you will need to purchase a 2 x Barlow lens. With a Newtonian of, say, f/5 or f/6, you will need something like a TeleVue Powermate; the 5x version is excellent (Figure 7.2) and, because it is in a 31.7-mm housing, is far cheaper than the 50.8-mm 4 x Powermate. Eventually you will experiment with focal ratios as high as f/30 or 40, but f/20 is a good place to start. Bear in mind that the precise f-ratio will depend on the distance over which the image is projected by the lens. A 3 x Barlow lens projecting 100 millimeters beyond the top surface of the unit will become a 5 x Barlow and a 5 x Powermate projecting 100 millimeters further than that point will almost become an 8 x Barlow.

Telescopes Mastery

Telescopes Mastery

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