Arberation inspector

Michael Gorman:
Is this without any changes, or after making a minor change.  If you make a tilt/back focus change the numbers will vary a lot as focus is also affected, so you need to refocus and that's not always exact depending on the seeing conditions in my experience. Even things like temperature changes can affect these numbers over time.

Linwood Ferguson:
I believe the randomness gets worse with fewer stars.  AI needs a dense star field in all corners as well as the center.  It will run with few, but I think (based on observation not knowledge) that it gives less consistent results as the number of stars get less.   I do not know if that is your problem, but I do know it works better as you get more stars; try finding a really dense area and/or lengthen your exposures.

John Hayes:

Christian Bennich:
Hey

I am trying to get better at controlling tilt and backfocus. I am working with my Octopi. 

Have you ever seen the numbers in the Arberration inspector jump around like this?
I am NOT making any changes between these runs - and the numbers are ALL over the place.

Any input or advice?
I suspect that even very little wind might cause this.

My suggestion is to use whatever method you like (in your case, aberration inspector) to minimize tilt and to then check it with a Bahtinov mask.  Point your scope at a large open cluster with a lot of relatively bright stars and shoot a few 30s - 45s exposures with the B-mask on the scope.   Then zoom in to examine the patterns over the whole field.  If all of the patterns are perfectly symmetrical into all of the corners, you are done and you can stop adjusting things.  The B-mask test is quick, easy, and unambiguous.  Using a "long-ish" exposure averages out seeing effects so that you can pretty easily tell whether stars are in or out of focus.  This isn't only a good way to cross check your results.  I've used this method as the primary way to shim out tilt on the camera on my system in Chile.

John