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Message: <blockquote data-quote="Hans Weigum" data-source="post: 3640857" data-attributes="member: 70218">Some time ago I started, but not yet completed a systematic comparison of different means of "externally" modifying magnification of telescopes (including binoculars) by means of teleconverters (alias extenders, doubler,..). I came to the conclusion, but cannot yet proof it, that optically relatively simple galilean (or, sorry to Jan and Gijs: Dutch) telescope concept teleconverters in front of the objective as discussed:<a href="http://pages.mtu.edu/~shene/DigiCam/User-Guide/FZ-30/Converters/Lenses/Telephoto.html" target="_blank">http://pages.mtu.edu/~shene/DigiCam/User-Guide/FZ-30/Converters/Lenses/Telephoto.html</a>tend to generally perform better than much more sophisticated devices put after the eyepiece. Brightness and field of view suffering obviously with a device put after the main telescope. But more interestingly I could never so far observe a clear gain in resolution with this set up.Discussing this observation with experts inside and outside industry I was told, that most, even expensive binoculars, have only correction adapted to the performance of the human eye. A teleconverter put after such a binocular therefore cannot improve the performance of such an arrangement.With better corrected telescopes, offering dedicated teleconverters put between prisms and eyepiece, the situation should be different. HW</blockquote>