Rather than hijack another thread, I thought I'd start one of my own on this topic.

I got some ruined sheets of 14x17 x-ray film in the mail today, and I plan to use them to build a ULF camera. It' a long-term project, with no planned completion time, but the film holder is obviously the place for me to start. I'm wondering what others have used for septums in their big film holders. Rigid, thin, and lightweight are not an easy combination.