What is "viewfinders"

Usage examples of "viewfinders".

He leaned against the railing next to a row of chit-operated viewfinders trained in the general direction of the New York Dike, looking like any of the other single men and women scattered across the observation deck.

Now lots of girls have got chintzy little viewfinders that movie guys give them, but this was an expensive one, on a chain, with a little velvet case.