wuzzagrunt wrote:Magnification ≈ focal length (mm) ÷ 50
A 50mm lense is aproximately 1X. To get 30X, you need 1500mm of focal length. A 1500mm photograhic lense for an SLR camera wil set you back a bit. Most good spotting scopes are about 1500mm focal length. The focal length of porro prism optics is generally longer for a comparable unit than roof prism instruments.
The best bang for the buck is probably a good quality cadioptric telescope. Something like a Celestron C6-S Schmidt-Cassegrain is very compact and has a 6" objective lense, so it has all the exit pupil you can use for natural light photography. Long focal length in a much shorter package than a refractor scope. Even the best refracting spotters (like the Leica) max out at about 60X because of the <4" objective. The C6 (or equivalent competing brand) has 6" of objective and costs less. It's not quite as portable as a compact spotter and there are columnation issues but everything is a compromise. Also, astronomy scopes are not generally waterproof to any significant degree.
franchi_612 wrote:Zoom is the max focal length divided by the min i.e. 3x zoom could be 25mm-75mm or it could be 100mm-300mm etc.
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