Strange SemiCircles?

[tony_cameraguru]

Hi

Despite imaging M42 on separate nights, and in two different locations in my rear garden, I am still getting these strange semi-circles on every light sub and in the exact same areas.The view is clear of any obstructions, and both nights were clear. This occurrence does not affect any other light subs, and I collected data on M45 the same nights. I have not seen this on any other DSO images that I have shot. Equipment: Explore Scientific 80ED APO Triplet; Explore Scientific Field Flattener; Canon 250D mod; UHC filter. Will this phenomena clear during stacking with darks etc in APP? 

Thanks

[vlaiv]

I'd say this is freak occurrence of a lens flare.

Two very bright stars are in direction of centers of circles. There are other brighter stars than Mintaka in belt, but they were not in "the right place" to produce lens flare. It seems that Rigel and Mintaka were about the same distance from optical axis and in the sweet spot to produce some sort of lens flare effect.

I could be wrong with this, but it does seem like likely explanation.

It will not clear with stacking - it will compound, so you'll either have to live with it or process it out.

 

[Laurin Dave]

To me they look like internal reflections from some part of your optical train caused nearby bright stars (Orion being full of them)...   the one to the top right is brightest so looks like its caused by Rigel, bottom right by Saiph and the left one by one of the Belt stars.   With the camera off take a look through your scope in daylight  and see if you can see any bright edges if so they need coating with antireflective paint or flocking.  The size of them would suggest to me that its the flattener

[vlaiv]

14 minutes ago, Laurin Dave said:

To me they look like internal reflections from some part of your optical train caused nearby bright stars (Orion being full of them)...   the one to the top right is brightest so looks like its caused by Rigel, bottom right by Saiph and the left one by one of the Belt stars.   With the camera off take a look through your scope in daylight  and see if you can see any bright edges if so they need coating with antireflective paint or flocking.  The size of them would suggest to me that its the flattener

I did not even notice the third one - but yes Saiph looks like culprit for that one.

[tony_cameraguru]

I think I have tracked the problem down, as the flattener comes in two parts. the correcting lens and the sleeve. I took them apart some time ago to easily clean the lens, and I screwed them together wrongly. The screw end is reflective silver and the opposite end is black, I replaced the sleeve the wrong way round so the reflective end was open to the imaging train. Hope this works now, but cloudy skies at the moment.

Thank you to all for helping me with this issue.

Clear Skies