>>289638450mm f/0.7 is after the conversion, since even f/1 is incredibly difficult to achieve using regular methods.
If we compare the scale of medium format (NASA used 6x6 Hasselblad) and super35 (about APS-C size), we can work our way backwards to determine that the lens was actually about 150mm f/2, which is a very reasonable design.
Kubrik did use an adapter during filming, but it's only function was to increase field of view to about 36mm, and it attached to the front of the lens, meaning it would have no effect on effective aperture (on the contrary, it lost some transmission).
