This extraordinary film is part of the 'Woman With A Movie Camera' strand at BFI Southbank. You can find more details here.
BFI Southbank introduction:
If you thought Lost in La Mancha and American Movie chronicled chaotic film productions, get a load of Joel DeMott’s eye-opening making-of documentary about 1977 horror flick The Demon Lover. Both funny and shocking – with a hilariously acerbic voiceover from DeMott herself – the rarely-screened Demon Lover Diary is one of the best films about filmmaking that you’ve never seen.
Village Voice review:
Joel DeMott and Jeff Kreines’s verite account of a bargain-basement horror flick being produced by a pair of ambitious Michigan proles is scarier than The Blair Witch Project, the indie of indies.
There is a more detailed essay on this documentary by Rob Newton in Film Comment whihc you can find by clicking the link here.
Here is the trailer.