Jill worked at the local photo and film DEVELOPING shop. She thought she already knew a lot about LIGHT and how to get the best picture COMPOSITION. She was good at adjusting the setting for the LENS to focus on subjects. She rarely got a bad REFLECTION or a BLURY photo. Her boss helped to educate her on the PROCESS of film development.
It was more complicated than Jill thought. They took the film into a dark room with special light that would not ILLUMINATE the film. They put it into an EMULSION. They could then see whether the film NEGATIVE was OVEREXPOSED or OPAQUE and not REPRODUCIBLE. They could also detect if the APERTURE on the camera was properly SENSITIZED. Jill appreciated his guidance because it was TRANSPARENT to her that picture-taking and developing required skill and technique.