Oh we all love our Panasonic 20mm f/1.7 Lens. But admit it we always wanted it faster. And if you thought that the f/0.95 aperture of the Noktor is as fast as you can get you were wrong!
On Ebay we just found the extream rare De Oude Delft 50mm f/0.75 lens (click here). The M-mount lens cost US $1,500.00 and you have to tolerate the fungus on the glass
But guys that’s a 50mm f/0.75!
If you want it faster you need to find the Carl Zeiss 50mm f/0.7. It is a Limited production lens built for the NASA space program- Stanley Kubrick used it on a 35mm movie cameras for some candlelit scenes in Barry Lyndon! Story of the Zeiss lens is available here: http://www.visual-memory.co.uk/sk/ac/len/page1.htm