Potential mis-alignment of .... something!

[daz]

I have been working on a project for the Eastern Veil over the last few weeks, and now have started the processing.

I have noticed that I have a definite 'smearing' of stars and I need to track down the reason! It seems to be OK at the bottom right hand corner, stretching up to the top-left hand corner, where things are definitely worse. I can probably rescue the images, to a degree at least, but of course would like to find out the root cause and eliminate.

My ED80 does not have a collimatable cell, but there are plenty of other areas for examination:

• Focuser alignment - Baader Steel Track that does have adjustment capability
• Filter tilt in filter wheel - unlikely, but will check
• Lens alignment - the doublet may have a stigmatism when the lens are oriented in a specific way
• Camera square in draw tube

I am going to invest in an artificial star, and after reading this (amongst others) I have done the maths (I think!!) to work out spacing and distances for the various elements needed.

I attach some images showing an OIII image, Ha image and the results of running FWHM Analysis in PixInsight. You can clearly see the slope from the b/r to t/l corners...

If anyone has any other insights, feel free to comment - otherwise, I'll post uipdates as and when!