The Asphyx [1972 - UK] sci fi

Hugo is a brilliant mid-Victorian scientist, loved and respected by his family and friends, admired by his colleagues. But he is a man quickly becoming obsessed with a curious and frightening question... what is the mysterious apparition found in the photographs of his dying subjects? Hugo brings to a family boating party his newest invention-a motion picture camera. The party quickly turns into a disaster as he captures on film the tragic drowning of his wife and son. When the film is replayed later, the same ghostlike presence appears. It flies towards his son, and vanishes inside his dying body. Has Hugo discovered The Asphyx, the spirit of the dead described in Greek mythology? A spirit which lives in constant agony, not finding rest until it takes possession of a human body? Could the spirit, if captured, become the key to immortality? Hugo is compelled to find the answers. It is a ghoulish search, with eternally haunting results.