Fantastic work Terry, congratulations!
Here's my effort from this morning - no slit so I thought I'd do better at a wider scale (55mm) to reduce the comet to as small a size as possible. Bad logic, the spectrum reduces in scale too!
Had issues with light cloud, heavy dew & car headlights in getting what I got. The severe vignetting is because I shot with an ordinary camera lens with the grating set in an old lens cap - it acts as a very restrictive aperture mask.
Anyway, pretty pleased, first time I've had a try at a comet. I 'borrowed' your calibration Terry as I haven't done a decent calibration for 55mm shots - thanks.
Cheers -