Here are a couple of documents from the Schneider web site -


See page 6 for reference to the 'self-closing slot':

http://www.schneiderkreuznach.com/ar...apo_14_760.pdf


See page 2 for more info (not in English) and images of what I'm guessing are a 'gelatine filter' holder and a 'matte':

http://www.schneiderkreuznach.com/ar...pro_claron.pdf