The USB digital eyepiece for telescopes from ThinkGeek has adapter rings (24.5mm and 31.7mm) for use with any telescope. The eyepiece uses a 1/2 inch, 1.3 megapixel image sensor to output images to your computer via a USB cable. You can view or save 1280 x 1040 video or photos to your computer. The USB Digital Eyepiece is $99.99.
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Interesting to see if it is any good. Cams of this kind tend to be useful only for solar system objects. Taking a large series of photos and using Registax to align and combine the images has been the preferred way to do it since the days of the Philips ToUCam, which many amateur astronomers still use to this day.
Unfortunately, NOT good. The USB camera interface they use is poorly implemented meaning you need to use their bad software. Also, the unit I got had a SWATH of dead pixels and the manufacturer would not replace it!