Help with star trails in corners

[jamenx]

Hey, hoping someone can help me with some star trails (see attached stacked image). This is the second time out with a completely new rig, so I am still getting to grips with everything.

Redcat 51, AIS2600MC Pro, AM5 mount. 

Images: 37 - 300 sec lights, 30 - darks, 30 - flats and 100 - bias.

I have star trails at each corner moving away from the centre. What's the most likely reason for this? I am still getting used the mount and setup so only did a very quick polar alignment and my guide cam was not fully focused if that makes any difference.

Thanks James

 

[jamenx]

Forgot to add I also used 2 inch Optolong L-eXtreme Filter

[michael8554]

I see very slight star elongation here and there, but not consistent.

You can't make these sort of judgements on a stacked image.

Look at one short stretched exposure, to eliminate guiding and stacking artefacts.

Michael

[inFINNity Deck]

IMHO the elongation is very consistent with wrong flattener to camera distance where the camera is too close to the flattener.

Nicolàs

[happy-kat]

Doesn't the redcat 51 have a petzval design eliminating a field flatenner?

Edited February 5 by happy-kat

[Stuart1971]

The redcat is a Petzval design with built in flattener, and so backspace is not an issue, BUT there is a common issue with these scopes where with APS-C size sensors there is some elongation of stars in the corners, I have heard of this a lot, nothing can be done about it, it’s just poor QC from William optics, but you could return the scope and try another, or if you are happy to accept the issue, and use Pixinsight then get BlurXterminator, as that will fix the stars no problem at all in processing..

[Stuart1971]

6 minutes ago, happy-kat said:

Doesn't the redcat 51 have a pretzel design eliminating a field flatenner?

Pretzel…😂😂 you mean Petzval

sorry made me laugh….

[happy-kat]

I did but shucks you stashed a quote before my correction 🙂

[Stuart1971]

Just now, happy-kat said:

I did but shucks you stashed a quote before my correction 🙂

Sorry….

[inFINNity Deck]

57 minutes ago, happy-kat said:

Doesn't the redcat 51 have a petzval design eliminating a field flatenner?

Indeed, and if I am right, all lenses have positions independent of the focuser (i.e. not like a field flattener for an APO that moves with the focus-tube), so then there must be something wrong with the internal spacing or (one of?) the lenses...

Nicolàs

[Stuart1971]

2 hours ago, inFINNity Deck said:

Indeed, and if I am right, all lenses have positions independent of the focuser (i.e. not like a field flattener for an APO that moves with the focus-tube), so then there must be something wrong with the internal spacing or (one of?) the lenses...

Nicolàs

Correct, and a common issue with these scopes, and shows in APS-C size sensors and full frame…you are lucky if you get one that works as it should with these size sensors…☹️

[powerlord]

If it's new, gather evidence from single subs, and raise with where you bought it. If it's FLO, I'd imagine they'll be no problem replacing it.

If on the subs it is just one side though, consider that it could be tilt - your asi2600 has a tilt adjuster - but don't mess with it until you are sure the issue is tilt.

stu

[Stuart1971]

47 minutes ago, powerlord said:

If it's new, gather evidence from single subs, and raise with where you bought it. If it's FLO, I'd imagine they'll be no problem replacing it.

If on the subs it is just one side though, consider that it could be tilt - your asi2600 has a tilt adjuster - but don't mess with it until you are sure the issue is tilt.

stu

I don’t think its tilt, as all the corner stars elongate towards the middle, it the age old issue with these scopes, poorly fitted flattener element in the scope, but as I said BlurX would sort, no problem….😉

[jamenx]

Thanks for all the info. I’ve checked the individual subs and it is noticeable in all four corners in each sub. 

I’ve also tried Blur X and it does indeed fix this completely in the final image.

I’m in a bit of dilemma now whether to send it back for a replacement, which presumably could have the same issue? Or just correct with Blur X…

[Stuart1971]

1 hour ago, jamenx said:

Thanks for all the info. I’ve checked the individual subs and it is noticeable in all four corners in each sub. 

I’ve also tried Blur X and it does indeed fix this completely in the final image.

I’m in a bit of dilemma now whether to send it back for a replacement, which presumably could have the same issue? Or just correct with Blur X…

Yes a dilemma it is….personally, the scope should be good without the need to fix with software, if it was me I would  return, no doubt…it’s not as it should be and so not fit for purpose….

What would you do if there was not BlurX, that is your answer….👍🏻

[jamenx]

23 hours ago, Stuart1971 said:

Yes a dilemma it is….personally, the scope should be good without the need to fix with software, if it was me I would  return, no doubt…it’s not as it should be and so not fit for purpose….

What would you do if there was not BlurX, that is your answer….👍🏻

I have contacted the supplier and sent the attached to subs. They said it could be a manufacturing defect, but also said it could be tilt and referred to the top right hand corner of each image where the stars have a more uniform look.

They are going to contact William Optics, but suggest I do try to adjust the tilt to see if that helps.

[Stuart1971]

3 hours ago, jamenx said:

I have contacted the supplier and sent the attached to subs. They said it could be a manufacturing defect, but also said it could be tilt and referred to the top right hand corner of each image where the stars have a more uniform look.

They are going to contact William Optics, but suggest I do try to adjust the tilt to see if that helps.

Tilt would not make 2 opposite corners point to the middle, IMHO…