In The Departed (2006), before meeting Dignam and Queenan in the Special Investigation Unit building, Sullivan is framed in a small circle as he stands near a traffic signal, which enlarges to full screen:
What's the meaning of this effect?
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An iris shot is a technique used [...] to emphasize a detail of a scene above all others, more commonly to end or open a scene. Iris shots are also used to put emphasis on a particular aspect of film, usually something of importance.
This isn't a technique that's used a lot nowadays as it's more of an old-fashion way to emphasize. It can also be a tribute to the "old days" too.