Filters used in Polanski's "Cul-de-Sac"

[Fabrice Ducouret]

I watched Polanski's "Cul-de-Sac" yesterday, and thought that the black and white cinematography was incredible.
I am wondering what type of gradient filters were used for what seemed to be "day-for-night" scenes in which the actors are sometimes black silhouettes when they are under the dark part of the filter, and then bright again when they are on the transparent part.

I have some gradient filters, but the "dark" part isn't very dark.

[David Mullen ASC]

ND grad filters come in soft and hard transition edges, and in different strengths just like regular ND. Generally I find that for normal stuff, ND.3 grads are too subtle and ND.9 grads are fairly obvious, so 90% of the time I use an ND.6 grad -- but it sounds like you are looking more for an ND.9 grad.

[Fabrice Ducouret]

Thank you very much David! Very humbled to have an answer from you :)