I spent the weekend fiddling around with the new Canon 8 - 15mm L fisheye.
This must be the coolest lens I have used. It really is a fun lens, allowing the user to play around with various distortion effects. Build quality is top notch. Its a funny looking lens. The front element is essentially a dome shaped protective cover. No front filter here boys (and girls), so protecting it from scratches is a real issue. At 8mm on a full frame sensor it gives a true 180 degree circular image. A real clunky feature is that the lens hood has to be removed to use it at anything less than about 12mm on a full fram camera. I haven't tried it on my 1d IV yet.
15 mm indoor shot - takes in a 6 x 6 m room side to side and top to bottom. At least 30% of this image has been cropped away.
close up view of a lily - I had to clone my feet out lower left.
A real natty lens. I can't wait to really have a go at some decent shots with it.