"If it can be written, or thought, it can be filmed..." STANLEY KUBRIC
A-Wind and B-Wind
From Encyclopedia PRO
A-Wind and B-Wind is the emulsion position of the film. There are two possibilities, just as there are two sides to a piece of film. Camera original is B-Wind. A print struck from it will be A-Wind. This is because film is printed emulsion against emulsion.
When a roll of 16 mm film, perforated along one edge, is held so that the outside end of the film leaves the roll at the top and toward the right, winding "A" should have the perforations on the edge of the film toward the observer, and winding "B" should have the perforations on the edge away from the observer. In both cases, the emulsion surface should face inward on the roll.
To tell if a piece of film is A-Wind or B-Wind hold it up with the emulsion facing you. If it is A-Wind the image will read correctly, if it is B-Wind it will be mirror image.
A-Wind and B-Wind material usually cannot be mixed, unless you don’t mind things being mirror image or some material being soft in focus as a result of being printed base-to-emulsion (the solution is usually optical printing). But mostly, issues of A-Wind and B-Wind do not come up all that frequently. It usually only comes up when you have just completed your sound mix and the mixing house asks if you need a B-Wind track. If it is to be used with the negative from your camera the answer is “yes.”