This simple tip sorted this issue for me!
I recently tested the Lomography Petzval Art Lens, such an awesome bit of a kit! However I do have a tip or fix for one particular issue – I would like to add that I have hand and body tremor/pain which often results in me dropping things! Oops!
I found that the Petzval diaphragms can move around a little bit within the brass lens slot when you are out and about shooting images – and yes the diaphragms can fall out, if you shoot side-on in classic portrait mode. My tip and my fix for this was to loop all the diaphragms onto a light-weight carabineer clip (a simple metal loop with a spring loaded gate – often used in climbing).
This pretty much sorted this issue out for me, I used the unused diaphragms to good counter-balancing effect, which helped keep them together and they didn’t fall out after this. Results!
I am now thinking that maybe you could also use a key ring over or even cord or wire, maybe even string – have fun with your Petzval!