Emboldened by having two ‘D’ cartridges, I decided to dissect one to see what’s what.
Somewhere, I saw a complete Rapid tab letter to film speed chart but I can’t find it (I hate it when I do that). The charts I can find skip ‘D’.
One camera had CT18 film in it and had a supply side cartridge ‘D’.
This photo shows CT18 as being ISO 50.
The chart I found (A=25, B=25, E = 64, G=100, H=125, J=200, N=400) puts ‘D’ between ISO 25 and 64.
From this, I can be reasonably confident that a ‘D’ tab is ISO 50.
Edit: Found a more complete chart: A=25, B=32, C=40, D=50 E=64, G=100, H=125, J=200, N=400
I used to think the copper fangs helped hold the cartridge together. Once I really started looking at it, I decided they would interfere with the film if that were the case. Maybe they hold the felt in place?
It took me a while of pretty close examination to figure out that the ends are crimped on over a lip on the body of the cartridge.
The film is guided by (goes inside) the springy bits and around the outside of the plastic spool. No wonder it was so hard to push in a 24 exposure roll of film.
The system seems really complex but Rapid film was designed to drop in and wind without having to insert the film leader into the take-up cartridge. The spool/springy bits system would allow the film to exit flat across the feed sprockets and roll up inside the take-up cartridge without binding.
I think I can make a workable cartridge out of plastic.
For Rapid cameras that produce 24mm X 24mm images, this film is 16 exposures. The overall length is 23 7/8″ or ~ 60cm.
That’s it for now for my mini-adventure with Rapid film.