We all knew that the 500mm f/4 L IS was one of the best lenses you could buy, and Canon's most popular b-i-g prime lens. So what could they possibly do to make it even better?

Well, one immediately noticeable thing they could do was make it a lot lighter. The Mk II is MUCH lighter than its predecessor, to the extent that it's quite useable handheld. And the Image Stabilization system is improved, to 4 or more stops of anti-shake compensation. Take these two improvements together and testers have found that with good technique they can shoot handheld with shutter speeds down towards 1/15th of a second. Remarkable.

They've also given a substantial boost to its optical performance with Extenders - the new 1.4x III and 2x III versions. This means you can have a superb 700mm f/5.6 or 1000mm f/8 lens which is still hand-holdable. With the 1.4x Extender you'll still be able to autofocus on all EOS cameras, but if you want autofocus with the 2x Extender then you'll need a 1D-series camera or a 5D Mk III.

And of course, as you'd expect the optics, build quality, focus speed and focus accuracy are all outstanding. This is not a cheap lens, but you won't be disappointed.