Double Diffraction Spikes

[E_ri_k]

Hey guys, I was imaging M20 last night, had the collimation really good, and focus looked great, with the bathinov mask. However, I got these double diffraction spikes, but only along one axis.

(And one odd one that points out to the side, but I always see that one)

I thought it may have been a focus issue, but i'm not convinced, since my bathinov spikes looked perfect. I saw something about the spider vanes may not be equally spaced. Last time I checked they were, unless a fraction of a mm makes a large difference?

What do you guys think? Is there a good way of visually adjusting the vanes while looking at a star?

Imaging scope was 10" Newt, with QHY10 CCD.

Thanks.

[Shibby]

Double star? Or tracking issue e.g. backlash?

[Black Knight]

When I get this, it is definitely a focus issue. But I get it along both axis ... not sure why it would only occur along a single axis.

[Cornelius Varley]

It looks like a tracking issue. Your stars are all enlongated in the same direction.

Peter

[E_ri_k]

I thought double star also at the start, but all the bright stars had them, and the fainter ones too, but not quite as prominent. I have had a lot of trouble with tracking lately, but last night was pretty good I thought. Although it wouldn't surprise me if the tracking played up again

I'll play with the focus a bit more net time and look at the tracking to get to the bottom of it...

Thanks for the quick feedback guys!

Erik.

[Uranium235]

Hmmm, you also seem to have an extra spike at 11 o'clock. Something intruding into the light path? Also check your spider vanes, make sure they arent bent etc. It could just be dodgy focus though

[E_ri_k]

I know one vane has a SLIGHT bend in it, but I never thought it would show up o much on an image..?

[Jason D]

Check your spider vanes. If they are not aligned, they will produce double spikes.

See attachment. Left is ideal. Right is what could be the case for your scope.

Jason

[E_ri_k]

This is kinda what it looks like, very exaggerated, but there is a slight bend. I have never seen the double spike, the more I think about it, I think it is focus.

[Jason D]

While still on the spider vanes possibility, ensure that opposite vanes are inline.

[MikeD]

Like has been said, it looks like a tracking issue.

If you had round stars then I would look to the vanes.

Try a 2 second exposure on a bright star and see if the problem is still there.

Mike.

[E_ri_k]

Pretty positive it was dodgy focus. Had a play last night and I could see the double spikes appear and disappear as I focused in and out. Still have tracking issues though, I need to have a play with the settings in PHD.