The 1000mm Sigma we saw at PMA is nothing compared to this ultra rare Canon zoom. The retailer B&H photo has one of these, a 1200mm, F5.6 USM lens. They've been around since 1993, but are made to order at the rate of 2 per year, and there are less than 20 in existence. What the hell does 1200mm give you on a 35mm camera? A 2 percent field of vision. The cost? $99,000.00...USED. Shot of the zoom vs a standard 50mm lens, post jump. UPDATE: We've found bigger and badder 300X zoom and 5200mm lenses. [B&H, thanks to everyone who sent this in.]
I like how everyone points out how you can get almost the same thing for a lot cheaper - which is the exact reason they only make 1-2 a year. Because most people don't need the difference. For those that do, and can afford it, they make it. Pretty simple.
If anyone is curious, DOF at a half mile is about 300 feet on a full frame, so AF is pretty valuable.