Is it possible to have extension tubes on anamorphic lenses, for the purpose of focusing closer?   How does it effect the optics (beside the usual loosing infinity focus and such), and is there a difference between having it on a lens with rear-anamorphic element or one with front-anamorphic element?   Also, is it better to use diopters in this case? or are the pros/cons the same as on spherical lenses?   Thanks!