I am an advanced amateur using this lens primarily for bird photography. I will also use it for general wildlife and occasional sports photography. Coupled with my Canon EOS-1Ds Mark III body I can capture images of birds that I previously only could dream about. Incredible image sharpness astounds me. I have just recently received the new 1.4xTC III and 2xTC III and can't wait to try those with the 800/5.6. While many reviewers have mentioned the weight as an issue I don't have any complaints when I use my gimbal head and a sturdy carbon fiber tripod. That being said, I do notice a little shoulder fatigue if I carry the rig around for very long treks. Otherwise, the images that I can create with the pulling power of the 800mm focal length more than soothe the minor discomfort. If you are really into birding I strongly recommend this lens and the new third generation teleconverters. It's almost like having your own little Hubble telescope.

This lens is a dream come true. I shoot wildlife, often at a distance, and this lens is amazing. The lens is sharp as a tack and, when mounted on a gimbal head, very easy to handle. Auto Focus is super fast and quiet. Used a 2X converter and had great results.

My first extensive use of the lens was in Yellowstone and Grand Teton this past November. We hit all kinds of weather and the lens never disappointed. All in all I got some of the best photographs of my life. This lens puts you right there.

Lighter than the 600mm, The same size as the 600mm, almost the same field of view and a better I.S. make this worth the price jump. As sharp or sharper than any lens I own.

This lens is heavy, large and well, repeat WELL, worth carrying around. Autofocus is quick. Quality is excellent. Some have commented that long lenses are like looking through a drinking straw. I don't find the narrow field of view that extreme but still need practice in quick and accurate aim. I do wish the 800 would autofocus with a 1.4 extender but that does offer some practice in long-neglected manual focus skills. The Kata TLB-800 PL Lens Backpack has already proven itself excellent in getting the lens and camera to the scene of the action.

Ok, The best, yep I shot this lens and must say it is. Long and sharp, I only shoot it at 5.6. Birds, bikes, cars only with this lens. Opens up all new worlds and images to sell. Can't rent it, shoot with it for 5 years and then sell it for 15% lost, unreal for any lens! Go long!

I use the lens for photographing sea ducks, hawks, buntings and shy birds. It is very sharp and the tripod-sensing image stabilizer helps while the lens is supported. A Lowepro pack, good tripod with Gambel-type head and the lens weighs 34 pounds. It is tiring to carry around for any great distance. Using a Canon 40D with it is a bad idea and unless the light is very bright the pictures come out blurry. This lens is a people magnet and strangers will stop to chat, stare or quickly leash their dogs and keep walking. It attracts a lot of unwanted attention - be prepared to expect anything from the general public.

Almost weighs as much as my 500. Super sharp and fast focus. Very quiet image stabilization. Highly recommended if you need that extra reach.