it's a mirror lens for a camera, works on teh same principle as a telescope. find one
here on ebay
well, either of the sigma or tamron 70-300mm (35mm equivalent focal length of around 480mm) lenses will give me slightly better zoom than my s3is (12x zoom, 35mm equivalent focal length of 454mm) add a 2x teleconverter onto that and i'm looking at a lens with a 35mm equivalent focal length of 960mm at full telephoto. assuming my lens maths isn't off.
i like that.
would give me mucho nice photos of distant things. i daresay that my better option is defnitely a 70-300mm zoom lens. and pickup a 2x tele converter along the way.