http://medfmt.8k.com/mf/fast.html
The fastest lens I know of is the 50mm f/0.519 designed in 1959 by Yoshido. It uses aspheric elements (5 elements in 3 groups). The rear element is practically in contact with the film. The lens is about 100mm in diameter (of course). I suppose someone could calculate the depth of field; not much I imagine.