Вечера вуайеристов / Les Soirees d'un couple voyeur (1979)

Although she does not appear high on the credits, the female star is Morgane. She is married to Alban Ceray. They decide it would be fun to watch each other having sex with other people, and then they expand this to secretly filming the occasions so that they can watch them afterwards. Of the other females, Brigitte Lahaie does the most - and all in a fetching black wig.