Toronto. In the days of film, there was colour, colour negative, or black and white films of various speeds and contrast curves. You could buy rolls of 20 (later 24 and 27) or 36 exposure. The more frames, the cheaper the cost per frame, but you had to use all frames before changing a roll unless your camera had a knife feature.
For this feature, the Kine Exakta had a built-in knife – unscrew it and pull. Voila! you had a piece of film to process and you could save and replace the remaining unused portion. Some cameras, like the screw mount Leicas, had a separate knife (ABCOO) to cut the film in camera (great for the 75 and 250 frame Reporter models).
The idea of a knife faded in time and for at least the last three or four decades of its popularity, film cameras had no feature to cut the film for processing and replacement. Perhaps film became relatively inexpensive, or home processing disappeared, or commercial cheap processing blossomed and used only full rolls. Who knows?
The title comes from “Mack theKnife“, a 1928 song in the three penny opera, made popular in 1958 by Bobby Darin. and sang a couple of years earlier by Louis Armstrong. The lyrics were originally German. Translation into English occurred before Armstrong and Darin popularized the tune.