In these digital days photographers are used to instant development and changing the light sensitivity of your camera with the flick of the ISO setting. In days gone by (or for those who still love “real film” this was more complicated. You had to buy film with the required light sensitivity and you couldn’t just switch between photos. That sensitivity applied to the whole roll of film. So if you didn’t want to use say high sensitive film (e.g. ASA 400) for the whole roll you would have to wind on the whole roll and just get the bit used developed (or develop yourself if you had a darkroom and all the requisite chemicals). If you were really keen you could remove the film in a dark room or dark bag and come back to it later. The same principle applied to movie films including the popular supper 8 films for the basic amateur movie camera. Here are an assortment of movie films as readily used and available in the 20th century. In the 1970s most amateur film was silent (no sound) but sound super 8 movies soon came into their own adding a whole new dimension to home movies. As late as 1978 when I was married my camera was silent. My new father in law had been a serious movie photographer and has left many rolls of 16 mm film although it too was silent.