M45 - But why do I see spikes?

[cjdawson]

Hi all.

I had a go at taking an image of M45 using my SpaceCat51, and ASI 1600MM-Pro.  The image is a stack of 100 subs, in LRGB (100 of each) 60 second exposures, taken at 139 Gain.  Stacked in APP, then processed in photoshop.    It's turned out much better than my previous attempts on this target.

However, there's something that has been puzzling me.   The L subs have diffraction spikes from the bright stars.     I don't understand why, it doesn't happen on the RGB filters.  I took the camera apart and checked.  From what I can tell everything is optically clean.  but I did hit the filters with a lens pen just to be 100% sure, so do need to run some test images to see if the problem was solved by that.

 

Any other suggestions for what could be causing this?   p.s. the image is 4 hours of data in total (1 hour on each filter) and guided in RA using a Star Adventurer.

[carastro]

I had that happen to me once, and it was surmised that there must have been a hair or something in the imaging train, or possibly an overhead wire.

Carole 

Edited December 3, 2019 by carastro

[DaveS]

The last time I saw that it was due to a telephone wire I hadn't spotted, but there could be a hair in your image train.

[Laurin Dave]

Is it on all the subs? if so then its in the scope camera as Carole says.... if not then a branch or overhead cable as DaveS suggests... 

[carastro]

Yes I was going to say the same, if it's only in some subs, it's likley to be an overhead cable which passed through the FOV while you doing that particular filter.

Carole 

[cjdawson]

It's only on the Subs when the L Filter is in play.   And it's always in the same place.  Hence why I've already taken the filter wheel out, and given the filters - especially the L filter a clean with a lens pen.

[cjdawson]

With any luck, I think I have solved the issue with the L filter.  I think it was a bit of muck of some sort, and cleaning with a lens seems to have solved the issue.  Had just enough time to setup the scope, polar align but didn't get to M45 before then clouded over. (boo) so I took a 60 second exposure close to that part of the sky, don't think I caught any bright stars though.  But couldn't see any spikes on anything in the FoV.   hopefully it won't be an issue going forward.