At the recent APIS (Alternate Photography International Symposium) the
opposite was demonstrated and seemed to me to be a handier alternative. Air
under pressure is introduced into the frame, which is easier than trying to
maintain a vacuum. Perhaps another member of this group can provide more
details, as I am not in a position right now to go dig through my notes!
Sil Horwitz, FPSA
Technical Editor, PSA Journal
silh@iag.net