Galaxy NGC891 in the constellation Andromeda

Agreed. :)

I know about dithering, but it's difficult to implement on my mount. There is backlash on the declination axis. That's why the guide takes a very long time to recover. Half the session would be spent on that. So I do inter-frame dithering manually every, say, 10 frames. But apparently, I didn't make large enough shifts. I'll try to increase them.

ZWO CMOS cameras require mandatory dithering after each frame, which has been verified repeatedly. I prefer to spend 20-30 seconds of pause between exposures rather than later observing an irreparable pattern. I have a second mount just like this one; I set a 30-second pause between frames—that was enough. However, I completely disassembled it, re-greased it, and spent a long time adjusting it until I achieved a decent result. Now I can take 30-minute exposures with it, tested with an ED-80, with guiding, of course. On the main mount, 15-second pauses are more than sufficient. As for the EQ3, the Dec axis is certainly a real headache.

For me, it's not 20-30 seconds. It's with a large...

Well, I somehow managed to beat that pesky axis. Sometimes it hangs for a long time at some point, but mostly it completes within 30 seconds. It produces little waste. Ekudrive rules, thanks to Ruslan Korop.

There's a chance the guiding restarted. And between 30-minute exposures, you can lose even more time. But between 2-minute ones... Actually, I think I made small shifts. On other shots, the banding seemed to be mostly eliminated. Today, I captured another series of frames with larger adjustments. I'll stack them and see how it looks. :)