The field rotation is a dead giveaway for poor polar alignment.
To understand how accurate your alignment must be, you need to eliminate rotation from the guide star to the farthest edge of the imaging field. In your example, that's going to be at least 5 degrees. Then figure out the declination for your target - the closer to the pole the more accurate the alignment must be to avoid trailing. Then you have to ask yourself what is the minimum dimension to ignore star trails (5 arc seconds, 25 arcseconds, etc). Lastly, you need to know how long your exposure will be.
Based on those values, you can run the numbers and determine if you can reach the desired accuracy.
Move your exposure, scanning sensitivity, and center your guide star to get best results.
I made a google sheet a few years ago that allows you to run those numbers.
Then a colleague helped make it into an android app "Sky Drift Calculator"
On the choice of film, I've not been very happy with Ektar. I prefer Portra 400.
It will respond to airglow to give a green cast. This will have to be removed in post processing by setting the background value white balance. Select an area with a known dust cloud as your white balance. This will help the colors significantly.
You can overexpose C41 films. Try a 1 to 2 stop push as well.
For an example of what Portra 400 does:
https://www.dropbox.... Portra 001.tif
This was shot at 165mm on a Pentax 67 at f4 for 45 minutes with a 1 stop push.
Edited by SMigol, 10 September 2021 - 11:49 AM.