Colimation, tilt or?????

Could you post a raw unprocessed sub in this thread?   Doesn't have to be the actual raw file but export a raw sub as jpeg and just paste it here.  It's hard to tell from a processed image.

Hey Christian,

For me, the adjustment looks pretty good at first. It is difficult to judge, you should look at a picture without guiding influence,( Short exposure with high Gain/ISO).
The stars are a bit blured, this could be due to seeing or a less than optimal focus point -> Do you use a Bathinov mask or a Autofocuser?
The slightly frayed part of the stars are reflections: From the main mirror: you can have a ring printed/buy it or blacken the edge of the mirror. Or from the sec. mirrors, which are usually not colored at the factory.

CS Jan

I see a number of things.

1).  Your stars are mostly round from corner to corner, which indicates low coma.   That’s good.
2).  Overall your image shows soft focus.  That’s not so good.
3).  To my eye, it looks like the stars are more defocused on one side of the image compared to the other, which indicates possible sensor tilt.

Here is what I recommend:
1).  Point at a dense star field — like in the Milky Way.
2).  Use a B-mask to precisely focus on a bright star in the center of the field
3).  Start out with short exposures (~5-10s)  so that you can access focus from corner to corner
4).  Use a tool such as FWHMEccentricity in PI to look at the FWHM across the field to see how to adjust sensor tilt
5).  Once you have tilt corrected, use longer, well guided exposures (~ 180s) to look for coma in the corners of the field.  The stars should look round and equally small into the corners of the sensor.
6). Forget about the diffraction patterns.  The things that they might indicate are mostly irrelevant to the basic alignment that you are tying to do.

John

Christian Bennich:
I am using an autofocuser - I have considered a Bathinov mask as I think it's faster. The night imaging NGC281 was the first time with my Coma Corrector and it's absolutely possible that the focus has not been perfect. 

 I don't think I have ever hear about this: "From the main mirror: you can have a ring printed/buy it or blacken the edge of the mirror. Or from the sec. mirrors, which are usually not colored at the factory."

Will definitely look into that - I guess it's Mirror Flocking - correct?

Whart i mean was a ap.erture Ring for the main mirror: https://teleskop-austria.at/Blende250#m

a the end of tommy ´s Newton Primer, you can find some problems and their solutions. https://teleskop-austria.at/information/pdf/FN25010c_Photonewton_Justage_Primer.pdf