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Hi all, thanks for your comments here.
Yes, the purpose of the image was to focus on the SN and its separation from the bright field star next to it. Also, I wanted to show the unusual red/orange colour, which as Glen wrote above, is due to the galactic dust and cold gas dimming it. Normally, a SN explosion is much whiter, almost blue, so this one is particularly interesting due to its location within NGC5128.
The key to achieving a clean separation is to tailor the exposure time to the stars, not the diffuse glow of the galaxy. So, using RGB filters, I limited the exposures to 60 seconds each, and then combined them. The other reason for keeping the exposures short is to avoid saturating the pixels to their maximum value, which would result in a white appearance. By keeping the subframe exposures short enough, the colour of the SN, and other faint stars for that matter, can be captured too.
Of course, you need a steady sky, and a long focal length too. I'm very lucky at Runaway Bay because my scope is 3 floors above the ground, so I avoid close ground currents, and I also have plenty of clean laminar air flow from the Pacific Ocean 500m away which is more uniform in temperature than if it flowed over suburban landscapes before it gets to me.
So, while I may have one of the worst locations for light pollution, it is surprisingly great for steady seeing.
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