Interesting test. Thanks for posting. Given the spectral response curve for Ektar 100, the green or cyan shift we've both noticed in long exposures, and the relative brightness of the North American Nebula, Pelican Nebula, and emission nebulae around gamma Cygni, I'd say it looks like the red response is failing more rapidly than the blue and green.

For f:2.8 and 30 minutes, it doesn't appear that Ektar 100 is an outstanding candidate for astrophotography. Usable, I guess, but not with the best of astrophotography films over the years.

Lee