http://nexflowair.com/air_knife.php A Model 10003 3" Standard Air Blade™ Air Knife is mounted such that the surface of the Air Knife is flush with the surface of a camera lens. The air flows along the surface of the Air Knife and continues along the lens due to a boundary later effect that effect provides a laminar "barrier" to the dirty environmental air, keeping the lens clean and dry.(by Nex Flow™ Air Products Corp.)
