The Asphyx (1972) (Blu-ray)

Brilliant Victorian aristocrat and scientist Sir Hugo Cunningham has a morbid fascination with photographing the dead. But when his son's death in a horrific boating accident is caught on film he discovers that a mysterious creature, the Asphyx, appears at the point of death to consume the soul. Sir Hugo theorises that if he can capture the creature when it appears and lock it away he can achieve immortality. Together with his soon to be son in-law Giles, Sir Hugo embarks on a dangerous and all-consuming quest to give his family eternal life - but as his obsession takes over and his experiments start to go wrong...