Sigma 70-300mm f4-5.6 APO Macro Super II
 

The Sigma 70-300mm f4-5.6 APO Macro Super II is overall a pretty good budget lens. It's the best 70-300 available on the Nikon system, though it falls short of Canon's EF 75-300 f4-5.6 III USM.

Sharpness is good at f5.6, I've gotten plenty of detail out of it when it is in proper focus, it's better at f8, though not by much. The sweet spot is f11 (it doesn't get better after that)...

Colour is good as well, I haven't seen any problems with it.

AF is another story, it's pretty slow and Noisy on my D70. I've only gotten linear flight shots out of it, with birds and aircraft. It focuses at about the same speed as a Nikon 80-400mm VR. The slow focus has driven me to using the AF-S mode (focus priority) on my D70, that way, it only takes a photo when focus is locked, and with the release pressed all of the way down it does so the instant it achieves lock. (I never preferred AF-C anyway, I prefer every shot to be in focus to having lots of throw-away shots.)

I'd recommend it if you need a budget tele as I did when I got mine, especially if you're using Nikon gear. If you're shooting Canon though, you may want to go for the Canon's EF 75-300 f4-5.6 III USM, even better get the IS version of it, if you can spare the extra $, £ or euros...