I have now collected more data with the RASA rig and widened the image on what to me looks like a big (2° wide) Oiii emitting bubble associated with the Cone nebula complex. At first I thought it could be an SNR, and parts of it is just that. As you see from Marcel Drechsler's comment below the bubble is not one but several independent objects, and part of it is indeed a filament from a SNR, called the Monogem Ring. This is a huge (25° diameter) SNR visible in X-ray but rarely detected in visual light (see
https://arxiv.org/pdf/astro-ph/0511546.pdf) so this is one of very few filaments imaged visually so far.
Other tings to be seen in this image include the recently discovered Strottner-Drechsler 155 PN (
https://www.astrobin.com/vy1kma/), which is the Oiii patch of nebulosity up to the right, and Hubble´s Variable Nebula - the small arrow head like object down to the right. Then of course the image includes the Cone and Christmas Tree nebulae complex near the bottom and the Dreyer´s nebula near the top edge.
With the help of my Samyang 135 piggybacking on my RASA-rig you can see this image in a bigger context here:
https://www.astrobin.com/full/swnhqb/0/
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