http://www.nikonchat.com/nikon-digital-telephoto-lenses/

I recently purchased a digital camera lens yw/300mm 50/500mm I can not see any differentiation. Why indeed 300and 500mm
The camera Nikon D50 is a Nikon w70/300mm, and a Sigma 50/500mm. When I took pictures of an object with two full telephoto lenses did not see much difference in the photos. The object was almost the same size. Someone can help me understand why this is?
Well, that depends on the distance between the test shots taken. Remember from this date, not a Nikon full-frame camera, not that bit multiplier of 1.6 involved. Thus, the 300mm is a 480mm and 500mm is an effective 800mm effective. The differance is almost double. You should see a noticeable differance say, 200 feet, 600 feet Vers. Set some test shots differant distances, for example, 20 feet, 50 feet, 100 feet, 200 and 400 feet and then compare the differance. In doing so, you're learning the limitations of his gear. Good luck and happy shooting!
TLS800 Telephoto Lens System from Swarovski Optik – digiscoping