<p>I owned a 600mm f/4.5 lens, and found it disappointingly soft. I used a heavy Gitzo tripod and a Foba SuperBall head with the lens and usually shot Provia 100 film. I would think using it with a Sony Nex camera would result in even more disappointment. On the other hand, the well-known bird photographer Artie Morris at the beginning of his career used the 800mm and a T90 with great success.</p>