My take on this lens results in equal amounts of email from Sigma Fanboys saying I’m overly harsh and Nikon Fanboys saying I give this lens too much credit. So I must have it just about right.

What we have here is a very unique lens: there is no other f/2.8 zoom in this focal length. No one even tries. It is THE only choice if you need a 300mm f/2.8 lens but want to be able to zoom out. So that’s your choice: 120-300 f/2.8 zoom or the Canon 300mm /f2.8 prime. To make the choice easier, the Sigma 120-300 is quite a bit less expensive than the Canon 300mm f/2.8 and not very much larger.

The Sigma zoom isn’t quite as sharp in the center as the Canon 300mm /f2.8 (you won’t tell the difference in a 5 X7 print or an online jpg, but you might in an 8 X 10 print and certainly would in something larger). It’s definitely softer in the corners, but that’s usually not what you’re worried about with a telephoto lens.

Nearly as sharp, same aperture, it zooms, and all that at a lower price. That’s a tough formula to beat, but there’s always a catch. You will find the Sigma doesn’t autofocus as quickly or as accurately as the Canon 300mm /f2.8, especially in low light. If you expect it to, you will be disappointed. You’ll still get plenty of keepers, but you’ll also have more out of focus shots.

This lens also has a pretty high electrical failure rate. That failure may occur after shipping so you need to get this one a day early to test it out if it’s a critical shoot. And you might not want to take this on African safari as your only telephoto lens. Finally, if you have an older camera (read that as 2 years or more) we can’t predict whether it will autofocus with this lens – you should check the various online forums to see.