A null used viewfinder is a catch-all term to describe the sort of arty bollocks-speak one might observe being written or spoken by pretentious arty types. Named for a particularly pretentious photographer who used it in a caption for one of his (spectacularly dire) photographs. Also rendered as 'used viewfinder, null', or 'used null viewfinder'.
"Did you see what that artist bloke, John B. Smith-Smith was saying in his column in the Guardian the other week?" "I read it, yeah, but there were too many null used viewfinders to be able to understand what he was on about. Pretentious gimp."