As an addendum to my review of a year ago, I now own this lens and can say that it is the best lens I own. Fantastic! Excellent results, even with the 1.4x teleconverter.
Incredible images. Comparing this lens to my other telephoto lenses, is like comparing a Cadillac to a Chevy. Owning this lens for someone who shoots wildlife is a dream come true.
My only experience with this lens is a 5 day period that I rented it. Having said that, I now have set a goal of purchasing this lens within this year.
Before getting this lens in my hands, I thought I would be able to handhold shots using image stabilization. While this is possible, to get the full use from this lens a high quality tripod or at least a monopod is really a must. I have found this lens is just too big to be handheld on any long term photo shoot. My arms literally ached after a day of shooting eagles along Lake Pepin.
And you will be noticed. I was glad that the others watching and photographing the eagles were merely curious. This lens attacks a lot of attention, potentially good or bad! Everyone is interested in it, how heavy, how much does it cost and of course, the quality of the images you obtain.
The results speak for themselves. I posted a few of the several hundred shots made with this lens. The clarity, sharpness, color and bokeh are superb! If you have 10 grand burning a hole in your pocket, this is probably your best investment!