My method is to hold the cart in my right hand with end that opens (opposite the counter) pointing to the left with the dark slide facing up (film label down). Then with my first and fourth fingers of my left hand, I push down on the two tiny sliding catches on the end while push off the end with a right finger or two. The sliding buttons move very little but the end cap will just pop right off. Then pull the dark slide carefully and the film septums (septi?) will spring up.