Specifications of the lens:
Focal length: 50mm
Max aperture: f/1
Min aperture: f/16
Filter size: 72mm
Blades: 8
Elements: 11
Groups: 9
Weight: 985g
Dimensions: 81.5mm x 91.5mm
Adapted from photodo.com
I found this rare lens in used-photography equipment store Aperture UK in London, where it was being sold for about 3300 pounds.
The lens was discontinued and replaced by smaller Canon EF 50 f1,2 L USM. It was the fastest EF lens so far.
Here are the samples at f1,0. Used camera: Canon EOS 40D, iso 400, raw converted to tiff in Photoshop w/o custom settings. The image is followed by 100% crop.
f1,0
f1,2
f1,4
f1,8
f2,8