Rodenstock 50mm f0.75 Xray lens XR Heligon

Think a Nikon f1.4 lens is bright? Or a Canon f1.2 50mm? This Rodenstock 50mm lens has an amazing aperture of f.075! Made in Germany and originally used for Xrays, but can be adapted for photography with a little work. Rodenstock also make some very well regarded Large Format lens.

This lens is suited to someone who likes to play with unusual gear, it won't mount to a camera as it is, but the results are worth it. It could be used with most cameras with a manual mode and removable lenses.

Article about mounting this to a camera is here

More sample images here.
This version is best suited to closeups