If you ever thought a long time ago what would happen if you attach a telescope or a spotting scope to a Digital Camera? Well I can tell you its still been done today and if you got the will to do it then all you need is £150 to start you off! Take for example the Panasonic GH2. It can be attached to a 75x Telescope for zoom ranges up to 5500mm. Yes thats a huge zoom. Its not the same quality as dedicated zoom lense but if your ok with that then just keep reading. You can buy a starter kit for the Panasonic GH2 with telescope + adaptors and all you need to get you started.
Take a look at that super-Tele Lens 1200mm-3600mm on eBay (Click here).
If you want to learn more about the use of telescopes on the Panasonic GH2 read the review on Luminous Landscape (Click here). They used the $1600 Vortex Razor HD spotting scope.As you can see the image quality s very good. So if you need a lens to spy a bit around like Jeff did in “Rear Window” from Hitchcock you might get one of those lenses