I am looking at getting a night vision scope. Not sure if I should be looking at the 2 Generation or the 3 Generation Scopes. I know that the 3 Gen would be better, but they are also $1,000 more. Anyone have any experience with night vision that can lend a hand? I am going to mount it on my AR-15 for varmit control. How far can you see and distinguish the target with each Generation?