Large Supertele Zoom Range. The 300-800 f/5.6 Sigma lens provides an obviously unique zoom range. It’s quite a sharp lens but perhaps not the quickest focusing lens you’ve shot with, so more appropriate for larger wildlife and perched birds. Birds in flight will be more of a challenge.

Constant f/5.6 Aperture. While many zoom lenses offer a constant aperture throughout their zoom range, this one is a bit different. To do so in a lens with this large a zoom range is just impressive.

You’re Gonna Want a Tripod. At almost 13 pounds and 21 inches long, this is a heavy lens and it’s not image stabilized. This is not a good lens to rent for your first time shooting a super telephoto. It requires very stable support (a heavy duty tripod and gimbal head) and excellent long-lens technique. Best images will be obtained with a remote shutter release and mirror lock up. We’ve tested it carefully but even in the shop soft images have been 100% because of user error – it requires excellent technique and some practice.

Bigger Is Better? Just for fun, Sigma’s marketing blurb on the 300-800: A perfect lens for surveillance use, its stealth black finish is unobtrusive and easily concealed. It’s 21 inches long without the hood. Just how easily concealed and unobtrusive is that?