Recently I saw an article about the new sony lens with apodization element. This element should basically be a piece of glass with a circular graduated filter, placed close to the diaphragm.
However, if vignetting would not be a concern (it can be removed in post processing) I can imagine it would be nice to have screw-on apodization filters.
Does such a thing exsists and if not would ik be possible to create something like it with a reasonable result?
Edit: I just found this source in which it seems to be possible to get reasonable results with an home made filter near the diaphragm.