Strange spikes...

[paul mc c]

Hello all,any ideas what is causing the spikes on Alnitak,using a frac with l-enhance, efw and reducer/flattener.

Paul 

 

Edited January 4 by paul mc c

[WolfieGlos]

I’ve only had this happen to me once. When I first bought my lenhance filter over a year ago I tested it on the NA nebula with the Evostar 72ed with flattener and a DSLR, and it seemed to happen on bright stars near the edges - see below.

I had the clip in filter for a DSLR (which didn’t clip, it just “sat” in so it was able to move around…until I taped it in), so I was under the impression that the filter was moving, it wasn’t square to the sensor and thats what caused the spikes. The below image was 2 hours if I recall and it didn’t happen in the first hour, but as the scope tracked the target it started to occur in the later subs and gradually got more pronounced.

It may have also been tilt/backfocus related as you can see below all over the image, but I’ve never had it happen since on any image or sub with the 72ed, and certainly not on my Starfield 102. Looking at yours, you may have some slight tilt/BF issue in the top left? Does it occur if you position Alnitak elsewhere in the frame away from this corner?

Hope that helps.

[paul mc c]

When the bright star is centered there is no spike and when off centre the spike is there...what do you think,loose filter.

Bit of thin cloud in first image.

[WolfieGlos]

Hard to tell, I mean my culprit does appear to have been a loose and moving filter. I assume yours is a 1.25" or 2" screwed fit, so surely that couldn't happen? Have you disassembled your imaging train lately? I can only think of taking the filter off and using a UV/IR to see if the spike still appears. If not, then try putting the lenhance back on and seeing if it still happens.

I can't see any trace of it in your image with Alnitak centred, but it's odd in your new image with it closer to the corner that you've gone from a more pronounced single spike to a fainter double spike? It's almost as if it's a diffraction spike from a reflector or Newtonian!

Does it happen in the other corners? Perhaps it is related to tilt, have you checked the subs in CCD or ASTAP?

HTH