I've noticed differences, but have never been able to compare the pupils in similar light. Is the difference not just that
Lamprophis (i.e. almost 100% nocturnal) can close up there pupils more, rather than actually having a different shaped pupil? Unfortunately I've never photographed a
L.capensis in low light levels, but here is a photo of
L.aurora taken in very low light levels. There doesn't seem to be as much of a difference as I originally thought, although I am quite sure that
L.rufulus (water snakes) never close down their pupils so that only a vertical slit is exposed.
We must remember that a photograph can hold just as much as we put into it, and no one has ever approached the full possibilities of the medium - Ansel Adams