I have had this lens for quite some time but have not used it for a while. I am currently using it for some indoor work.
It is a Kern-Palliard Switar 13mm f0.9 for Bolex 8mm.
It is almost a full stop faster than a f1.2 lens, but still slower than the Stanley Kubrick f0.7 Planar.
I got this about 20 years ago and they could be had for very little money. Now they are pretty hard to come by.
Are you thinking of the Canon 310XL and variants? I still have several in the drawer. Didn't communicate with the operator, couldn't be controlled but within their limits the 6.5-25.5 lens shot better footage than the 6-70/1.4 and 6-66/1.8 Variogons on my Beaulieus.
Another 'feature' is that the 0.9 lens only fits the NON-REX cameras. The advantage is a lower effective shutter speed than the REX-8 cameras. (no light loss from the SLR prism). Making it better for low light filming.
Calculated depth of field is pretty good wide open. In the picture the lens is set at the hyperfocal distance for wide open and the scale shows infinity to just under 20 ft.