I managed to get some backing shots of the star field for my image of comet Wirtanen that I captured back on December 15, 2018. This was taken under my typical red/orange zone light pollution which is definitely a hinderance with an object that has such low surface brightness (and the waxing gibbous moon was present in the western sky during about half of these exposures).
Anyway, I used a 105mm Nikkor AI-S lens at f/4.6 on a Nikon D5100 (ISO 800) and combined 295 subs that were each exposed for 20 seconds to produce the image of the comet (the 20s exposure is about the maximum given my level of light pollution, total integration time was 295 x 20s ≈ 98 minutes ). Then I took 376 subs using that same setup on two later, mostly moonless nights after the comet moved out of this field of view (to record the comet-less star field and the Pleiades). Note that my original framing on the comet was the same as taken in these later shots, it's just easier to process the star field when there is no comet in the background (and vice versa).
Tracking was done with a Celestron AVX mount.
Image processing with PixInsight (comet registration tool) and Photoshop CC2017. I had problems with both a light pollution gradient and some uneven image quality falloff from the lens so I ended up spending far too much time trying to make this look presentable. This would have been a LOT easier under dark skies and with a better lens. That said, it's been a while since there was a comet that was even bright enough to attempt from my edge-of-downtown location.
Edited by james7ca, 12 January 2019 - 08:19 AM.