It took me two full years to minimize the tilt with my Esprit 100ED such that I was satisfied with it.
The first thing I can say is that the large black rings that supposedly allow you to rotate the camera should be tightened and left that way. The rear back ring should be screwed in all the way clockwise until it's completely tight, and then the front ring should be clamped down on it hard. Sorry, but it's not going to allow you to rotate the camera unless you want to fight with tilt forever. I'm not the only person who came to this conclusion.
The second piece of advice is to consider getting a Gerd Neuman 48 mm CTU if your imaging train has enough room. I use a guide scope, not OAG, so I could afford to insert the CTU. Glad I did, because it was the first time I ever had good stars in all four corners.
The last piece of advice is not to get too dependent on analysis software. What you're really looking for is stars that are 1) round 2) in focus, in all four corners. I have used software to analyze the tilt, and when it said the tilt was gone, I still had obviously bad stars in one corner. I then adjusted the CTU back to where I started and use the "eye test" in aberration inspector to look at corner stars. If you can't see anything that bothers your eye, it's good enough, so just have at it. Who cares what the software says if the corner stars look good? So many otherwise fine images on Astrobin have obvious star distortions in the corners, so if your images don't, I feel like you're above the bar.
Finally, be prepared for slight changes in back-focus and tilt as the temperature changes outside. In going from summer to winter in my climate, I will need to make adjustments sooner or later, or just accept that the back-focus has changed a little over the preceding months.
Also, my Esprit 100ED has pinched optics and suffers from star distortions in cold weather, so there's nothing I can do about ugly stars in January - but it's still my favorite imaging telescope.
Thanks for the reply, it's very much appreciated to be hearing back from other users!
I have been doing more tests and did exactly what you are describing here with the rotator. I did 90 degree rotations from 0 to 270 degrees to see if there were any changes, ASTAP says there is some tilt - but I've been trusting it less and less due to the varying results it yields. The stars look good now, I have a small sensor (533MM) for now but it's going to have a 2600 on there sooner or later.
The vendor also says that the stars look good, but also stated that some of my test image sets has focus issues - which I found a bit strange as I was using the EAF and the AA+ autofocus routine for each frame/rotation. The tightening of the rotator might have made the biggest difference as it was originally a bit too far out. What I did notice though is that the HFD or star size became smaller as I rotated the camera towards 270 degrees, being at it's smallest around 180-270. This could be a simple case of other factors in the atmosphere but still.
After the adjustments I haven't been doing any NB work, so I haven't seen if the sharpness has improved for the nebula, but it was obviously something wrong with the first images I took with the scope.
This is from one of the first image sets, 300s Ha. The stars look terrible to me. And the nebulosity was far sharper on my Evostar 80ED.
This is from my red filter after tightening the rotator and rotating it 270 degrees before locking it down, 270 gave me the best values in ASTAP at the time, that's why I chose it. I'm not seeing the same kind of coma here.
I guess some kind of focus issue could be the answer to the issues that had me reacting in the first place. But I'm not quite sure what to change as there is no slip in the tube. I'm just hoping that it is performing better on sharpness on nebula from here on out.
