Hi,
With running out of the stuff myself I had a look around the net at the various suppliers. Not that it makes much practical difference but it appears the film grating is sold as 1000 lines/mm (25400 lines/inch) or 500 lines/mm (12700 lines/inch).
I also found a supplier of 532 lines/mm crossed grating material which is an interesting product. In theory that should produce a useable spectrum no matter what angle the meteor fall across the FOV. However there is a BIG penalty in magnitude as the light per spectrum would now be divided into 8 spectra, four at right angles to each other and 4 fainter at 45 degrees. It’s probably more of a novelty laser pointer effect filter but….
I can feel some olde fashioned optical experiments coming along….
cheers,
Bill.