Henry Cavill took to the sky Friday night in Chicago while wearing his Superman costume ... giving fanboys across the country an average sized lump of kryptonite in their pants.

Cavill was in the Windy City filming "Batman v Superman: Dawn of Justice" alongside Amy Adams -- aka Lois Lane -- and in between takes Supes was caught flashing his pearly whites.

Ben Affleck was not on set -- he was in L.A. for an event -- but y'know it's only a matter of time until we see both of them on screen ... battling cod pieces.