What is a spy lens? how does it work?

Question: What is a spy lens!? how does it work!?
Best Answer - Chosen by Asker:

The old spy lenses were a tube that fit over the front of the lens and had a mirror in it, so that you could aim the camera one way, yet take a photo at 90 degrees to the apparent direction the camera was pointed!. It was a big deal in the sixties when guys (mostly) wanted to take shots of hot women at outdoor concerts without them catching them!.!. As I recall the didn't cost much more than a UV filter!.Www@QuestionHome@Com