Hi David,
that's a great start.
I read that the IMX455 sensor has about 72% QE efficiency
at the 656 nm Ha wavelength which is very high.
https://www.qhyccd.com/uploadfile/20...5055202120.png
Why did you chose 5 minute exposures?
I'm not familiar with CMOS cameras.
Is there a problem doing longer exposures with CMOS?
I found with my QHY9m CCD that a 20 minutes exposure
was an ideal amount of time when using Ha.
cheers
Allan