One of my favorite things in comic books is seeing film techniques translated to still images.
Here’s an example from Astonishing X-Men #17 (Joss Whedon’s run).
These two panels show rack focus, where the focus shifts between foreground and background to direct the audience’s attention.
In the top panel, the beer can is in focus in the foreground. Wolverine’s face, in the background, is out of focus.
In the bottom panel, the focus shifts so that the beer can is out of focus and Wolverine’s face comes into focus.
Changing the focus like this tells the audience what to pay attention to: first the beer can and then Wolverine.
If this were in a movie, and not on a page, it would be one continuous shot with the focus changing. But you can’t have a continuous shot like that on paper, so it translates to two sequential panels.