H-Alpha Images Streaking...

[pete_81]

Went for North America Nebula the other night, and having already done some shots with astro-modded DSLR, thought to try Ha which would allow experimenting with the 7nm Baader, option for luminance layers (APP layering) and longer exposure experimentation.

Polar alignment was good enough for the evening (16" out) and plate solving successully pinned down the nebula. Guiding also running with dithering etc.

But when the first of the (5min) Ha images popped up, I noted the bright stars were streaking with ISO 200 so thought I'd up ISO to see if it was just a display artefact and same thing.

ISO 200

ISO 1600

Guiding looked OK with settings as used before, but obviously not sure what was going on. All 15 images were the same with streaky stars.
So reduced exposure to 2min and went for the visible (UV/IR filter) and those worked fine, so built up more images to stack with 2 & 3 min shots. No streaking on any of these.

Final stack from this session:

Any ideas what the trails are caused by? It was quite breezy, but assumed the 3min exposures would have had similar artefacts if it was the wind catching the scope.

 

[fifeskies]

I would inspect the filter to see if it has a smudge on it.

[pete_81]

Nope, filter clean. Was cleaned with IPA just before going into the filter wheel and all inspected before closing the wheel. It was more the 'jittery' star trail that it has:

To me, it looks like the guiding got lost for a bit. I had thought it was clear through the time the images were taken, and to all have the same effect (1hr15m) again doesn't fit this argument, bearing in mind the plate solving didn't need to move when changing to the UV/IR filter and target was bang centre.
Wondered if there was a dither setting wrong, but it's only using a couple of pixels every 3rd frame.
Best I can assume is the wind but seems odd that the shorter exposures (similar breezes) don't show (I didn't look at the guiding graph so it's more a lesson to watch and take diagnostics for everything if possible, hence doing the PA screenshot!).

Hmmm...
I'll do again at some point and watch guiding and so on I guess.

[michael8554]

The GuideLog, if there is one, should show what went wrong.

Michael