Ha FWHM Plot

Misalignment on the ED80

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…

So, time to get busy and start understanding optics in a bit more detail!


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