It depends what it is. Sometimes what seems to be a film is actually caused by the glass being damaged by the dishwasher. The harsh caustic used in many dishwasher detergents slowly dissolves glass! If you have decent glasses dont put em in....But if its silicate deposits or lime (which it often is) wash them in dilute acid (vinegar and water 1:1) then alcohol (vodka will do) and this should get it off.