Robin. A pretty neat article. Around the time when the comet was visible night and morning, I took a mixture of images on a Star Adventurer with a 300 mm lens. On some of the wide angle images with the standard 18-55 mm lens, I used a diffraction grating. I didn’t do anything with the images at the time, but meant to go back one day. The magnification with a wide angle is quite small though. Although the tail came out very bright and sky had a glow to it, I’m not sure if there was any faint diffraction pattern. I should go back and check in negative format. That was the night my car battery failed when I was out in the countryside and I didn’t know my location 🙁
Hi Robin This image was taken on 12th July where I went out. But I will have some others around that date. I will check. But I think I only tried the diffraction grating on 12th until it misted up then reverted to without grating. I can’t be sure of the orientation of the lines now, and at the time, I was puzzled by the lack of obvious spectra from some of the brightest stars (unless they were out of field).