Most powerful Nikon fieldscope designated ED82 weights 1575g and is 327 mm long (main unit). When mated with one out of 11 eyepiece lenses, gives you 25x to 75x magnification. Instead of eyepieces you can add one of camera attachments, FSA-L1 being the most advanced SLR variety. It has native Nikon F mount and built-in circuitry that enables aperture priority shooting mode with most FF and DX Nikon SLRs. This combo acts as 1000mm (1500mm effective with APS-C sensor size bodies) f/13 (non-variable aperture) telelens. Here I have tested this combo shooting some birds at 20 to 60 feet distance. Since Sigma 50-500 when combined with 2x Kenko DG teleconverter gives the same focal length and aperture (12.6 to be exact) I have compared both at infinity. At 20-100 feet range this relatively cheap solution (approx. 1000$) gives good contrast and saturation with neutral colours and very little chromatic abberation. Resolution is comparable to Sigma 50-500 with 2x TC: not great, but useable. At infinity it scores considerably worse and is not recommended for hi-res camera like D200. Birders on a budget purchasing both eyepiece and SLR adaptor will get one-stop solution for relatively reasonable ammount of money.