First shot through new scope - some advice needed.

[paulgrover68]

Last night caught me out by the absence of clouds. I had to do a hasty setup of the new scope - transferring my guide scope turned out to be a battle (ironically, the guide scope I ordered for the new scope arrived today).

Then had some battles with plate solving. Then I had a power cut, courtesy of the cat. 

End result was a very late state. I didn't really have plan so pointed the scope at the california nebula.  I was tired by the end of the session and my flats were not so good (you can see bottom right!).  The moon was also being a bit naughty in my part of the sky.

My main issue I have is the stars at the edges stretching.

The scope is an Altair 72 EDF with a 0.8 reducer/flattener. Camera ZWO ASI294. Backspacing is 55mm.  The focus is almost at  full extension

.

Grateful for any guidance. I'm used to Newtonians and on my 200PDS the coma-corrector fixes everything.

 

 

[geoflewis]

Hi Paul,

The image looks good to me, but I can't get it any bigger than the thumbnail to see what is wrong with the stars. When I click on the image I just get another one the same size. It does sound like it mght be a back focus issue, in which direction(s) are the stars stretching?

Geof

[P Holdsworth]

Hi Paul , you may have had some challenges with the set up but the final result is an outstanding image

[Gina]

Very nice indeed ? 

[paulgrover68]

Thanks all - I am really super pleased with how it turned out.  I'm going through that stage of ultra critiquing, which is all part of the roller coaster I have been riding for the past few months.  Aside from the small points I was very stunned by how well this came out (back in May I would never have thought I could have got a shot like this) I'll post the image up on to flickr and and link to it. That should show my issues a little better.

Stars are streaking out from the centre if that helps and it's toward the edge - so maybe outer sixth. If I can get a partially clear night I'm going to drop an extension ring and see how that goes.  It's better to see it so I'll do the upload tomorrow.

I think my plan over next week is to jump on even a partially clear sky and fiddle just with the camera position. My new guidescope arrived today, do I also have time to focus it in and point it as I want.

Just to add I sometimes think an imaging session that is challenging makes any result sweeter. Of course when it all runs well it's awesome, but wrestling an image from the jaw of disaster is kinda fun!  Also the cat has shown no remorse for knocking my power out.

 

[MarkAR]

Posted by: @paulgrover68

Stars are streaking out from the centre if that helps and it's toward the edge - so maybe outer sixth.

Sounds like you need a little more baakfocus distance. Is it even all round?

[paulgrover68]

@MarkAR Hi Mark - it seems to be a little radial -nor rotated around a point - more like driving in snow!  

 

Here's a link to a version on flickr - this is processed a little different and not cropped so it's more apparent.  I mean it might be refractor thing... but I suspect it's more likely down to me!

[TerryMcK]

Definite flattener issues in the corners of the Flickr version. Is the flattener matched to the scope i.e. same manufacturer?

[MarkAR]

Could well be the flattener. Radial egging does point to camera being too close. 

[don4l]

It looks very like the distance between the flattener and the image sensor is not quite right.

I don't know which way you need to go (in or out), but if you can add or take away some spacers, then you should be able to figure it out.  If the stars change from radial to orbital then you have gone too far.

[MarkAR]

This should help.

[paulgrover68]

Super - I'm at max extension with spacers at the moment.  I'm going drop one out and check if I can get focus. If that isn't the case (I think I'm too close.) I'm looking at adding a filter drawer, so I think that may give me some more space.

Thanks everyone!

Also scope is Altair EDF 72 and Flattener the Starwave 0.8 Reducer V3 (came with it)

[Stub Mandrel]

@paulgrover68 I suggest adding spacers 1mm at a time.

Also focusing at the 1/3rds point -  1/3 from the edge and 1/3 from the top - is a quick, simple and reliable way to minimise aberrations with almost any system.

[paulgrover68]

@stub-mandrel I will try that - I'm currently up and running, but I think I can do 3 targets tonight, so will refocus on the next one.

 

I found some shims in the camera box, I've introduced them now too. The sub look to be better, but not fixed - so I think I'm going in the right direction (pun intended... is that a pun? Let's call it one)