Now that it's finally nice, it's time to get out and use the Speed Graphic. I'd love to get a circular polarizer for it, but the lens itself doesn't have any threads for filters. It's got some sort of doohicky clamped to the outside of the lens ring that can be unscrewed and I've got some assorted filters that slip behind it. I can't seem to figure out what size the threads are. The local camera guy thought it might be a No. 6 or 7?? I've never heard that. A caliper says that it's approximately 44mm... Any ideas?