The Canon 800mm f/5.6L IS Lens
I've been looking at the Canon 800mm lens.'
Canon says "This is the longest telephoto lens among Canon's lineup, and a terrific choice for any long-distance application-outdoor sports, wildlife, news photojournalism, and so on. It's actually lighter than Canon's EF 600mm f/4L IS lens, weighing just under 10 lbs. It uses a refined optical design, with two fluorite lens elements, one UD element, and one Super-UD-glass element, for outstanding correction of color fringing and superb contrast and sharpness. This super-telephoto lens uses magnesium-alloy barrel construction to enhance its light weight, and has weather-resistant gaskets throughout for use in harsh conditions. It's compatible with both the EF 1.4x II and 2x II tele extenders for even more reach: EOS cameras with 45 AF points will continue to provide autofocus at the center AF point when the lens is used with the 1.4x extender. Finally, it's image stabilized, providing up to 4 stops of correction for camera shake. This makes it even more practical in many situations."

Art Morris of "Birds as Art" seems to have adopted this lens as his main tool for bird photography. I'm surprised not to have ever seen one of these lenses in Morro Bay, CA, where 500mm and 600mm Canon lenses are frequent.