Rokinon has updated their popular 8mm Fisheye lens to include better optics and now a removable lens hood. I recall some people needed to shave down the old version depending on the camera they were trying to fit it with. This will give you 180 degree viewing angle on APS-C sensor sized cameras. Although it can be mounted on Full Frame cameras like the 5D the image will not fill the entire frame. You can already find the Rokinon 8mm F/3.5 Fisheye lens available via B&H (click here) and also via eBay (Click Here)

Rokinon8mmHD