M51, RASA 8", 4 hrs (no filter)

A valid point. I completely agree. 400mm for galaxies is laughable.
That's why I don't even have a UV/IR cut filter, only a dual-band filter.

But what can you do when you have a RASA "barrel" and suddenly get clear nights? You have to use what you have.

You should try capturing Markarian's Chain. Or, as a last resort, M81 with M82. At least there's some dust across the entire frame there.

M81 is out of my field of view, but I'll post Markarian today—it's already processed. It just fit on the 400mm with a large sensor. Stay tuned!

BIAS. Median = 601 Lights at the center (this is important here due to very strong vignetting). median = 21111

That is, the offset is around 80. Overall, it seems everything is not quite optimal. However, such a high average could be due to the presence of a galaxy. Simply put, the optimal maximum exposure time for your parameters would be a few seconds.

Although such a high average might be due to the presence of a galaxy, I measured the average on a frame with Markarian's Chain, where there is no galaxy in the center. (Obviously, it doesn't make sense to measure the background on a galaxy.) I took a smaller area, but still right in the center: Image01->Preview01 count (%) 100.00000 count (px) 192304 mean 15545.7 median 17823.0 avgDev 4105.6 MAD 5213.6 minimum 10960.0 maximum 48029.0 And here is the entire image: Image01 K count (%) 99.99031 count (px) 26105821 mean 14555.4 median 14669.0 avgDev 3810.2 MAD 4602.0 minimum 8789.0 maximum 65510.0 There are "burnt" overexposures and well saturation, but only in individual stars. The main object is not overexposed. In this case, does it make sense to reduce the exposure?

The issue isn't that the stars are "blown out," but rather what the background looks like. The exposure should provide an optimal background level for a single frame and an optimal signal-to-noise ratio for the stacked exposures. There's a lot of information on this topic online.