Pourquoi choisir des longues-vues équipées de verres spéciaux ?

When you want to buy a spotting-scope, you have the choice between models with standard and fluorite-coated, high-density (HD) or extra-low dispersion glass (ED) lenses. Under normal viewing conditions and at low magnification, it is often hard for most people to tell the difference between scopes with HD, ED, or fluorite glass and those without, but if you zoom to high magnification through heat waves or in dim light, the extra sharpness, the chromatic aberration reducing and the enhanced colour resolution produced by these higher-quality optics can be readily apparent. And if you want to digiscope, these differences could be important to get better digital images. But HD or ED models are much more expansive than standard models, and this could be a real issue for several birders. based on several tests and comments, especially those of Rob Wilson on his website www.digiscopediary.co.uk involving T90 and T90 ED Olivon spotting-scopes, we try to help you for your future choice.