<p>I've been shooting with the Sigma 150 to 600 contemporary which weighs about 4 1/2 pounds. Almost all of the images of birds on the photo.net site that I have posted in the last month were taken with that lens. For the most part is extremely sharp except wide open at F6 .3 at 600 mm. If you shooting at F7 .1 or greater, you won't notice much difference in sharpness above 550 mm. It is extremely easy to handhold at 600 mm. The VR is very good. I use mine with a Nikon D750. Because the lens goes from F 4.5 to 6.3, one needs to be sure that they can shoot at mid range iso without noise issues. I don't seem to have any issues with my D 750. A nice aspect of this lens is the ability to change the firmware and customize it to your camera. I picked up mine for under $1000 and it easily comes close to 95% the quality of a $10,000 600 mm prime.</p>