His film career diminished during World War II and he also worked rarely as a cinematographer after the war as well.
The cinematographer Karl Hasselmann learnt the profession of a mechanic and he joined the film business in this function when he got a job in a repair shop for cinema equipments.
Karl Hasselmann only continued his film career after the end of the war and he was engaged again as a cinematographer for many productions in the 20s.
His experiences as a cinematographer were also regularly used in the 30s.
When the fictitious film became a more and more important factor in the film business Karl Hasselmann became a demanded cinematographer and he realised till to he beginning of World War I numerous movies.
He became interested into the new medium film and he began to shoot first movies as a cinematographer like "Der Hauptmann von Köpenick" (1906), "Andreas Hofers Tod" (1909) and "Die Erschiessung des spanischen Rebellen" (1909).