While studying thin-film interference on wikipedia, I encountered a problem. The picture in the link shows a colorful pattern formed on the oil film, that is, the oil film also acts as a screen on which the interfered light reflects and then enters our eye.
But the diagram for the derivation of the mathematical expression shows that the interference of reflected and transmitted light occurs somewhere above the oil film, that is, the screen is somewhere beyond the film, in air. I cannot understand that. (Derivation Image Link)
I think the third diagram is a correct way of explaining the colorful pattern because the upper surface of the film acts as a screen for the interfered light which also reflects the interfered light to our eyes so that we can observe the pattern.(Diagram image link)
Can anyone clarify?