Billy Williams was cinematographer on Russell's Billion Dollar Brain in 1967 through to Women in Love, The Rainbow and Dusk Before Fireworks in 1990, being nominated for an Oscar for Women in Love. His 46 film credits also include Sunday Bloody Sunday and Gandhi as well as the opening (Iraq) sequence of The Exorcist. Williams said he moved from documentaries to commercials, working with Russell, to films.

Above Williams with Ken Russell, below his cinematography with Alan Bates reflected in the mirror.

For more on Billy Williams click here.
https://iainfisher.com/russell/ken-russell-people-technicians.htmlThere is an interview with Williams talking of The Exorcist here
https://www.youtube.com/watch?v=OTEQ46Lv5NU&t=176s