Thanks Robin
Because the diffraction grating is only a recent addition in the last year, I have images through the CCTV camera without the grating, so I can hunt out a direct comparison frame. Bear with me and I’ll grab an image. I might be able to stack the two to see if any changes are obvious, but I might have to alter B, C, gamma, invert etc, to provide images that can easily be seen together as an overlay.
kind regards
Derek