Poor star shapes with William Optics triplet

[kirkster501]

Flattener spacings are absolutely critical and the faster the scope the more critical it becomes.  Even a fraction of a millimeter is all it takes to ruin the star shapes.  Are you sure the flattener is at the exact distance recommended?  Are you using the WO flattener?  Does it do this at all temperatures?  Does it do it pointing at the Zenith?  Have you overtightened the scope mounting?  Are you over tightening the flattener?

On another note, tools such as Blur Xterminator make a superb job of correcting star shapes.

Edited May 29 by kirkster501

[Albir phil]

Hi I have the same scope, I do however use the W O adjustable flattener/reducer, and never had any problem.So I agree best to use the dedicated F/R for the scope 

[Elp]

I would discard the test with your borrowed flattener, the backspacing doesn't look correct so you can't use it to make any sort of assessment.

Edited May 29 by Elp

[Megawatt]

On 29/05/2024 at 04:38, Stuart1971 said:

I would not take much notice of results with a “Universal” flattener, you need to be using the dedicated one to get best results, the only real way to test whether the flattener is the issue, is to buy another and if the problem is still there, then return it, you have 30 days to do this with FLO..😉

Well, if two different flatteners are giving the same poor result, it seems unlikely that a third flattener will provide a solution. 

One thing I did try it loosening the tube rings, and I don't want to get my hopes up but I do see an improvement. These were shot with the original William Optics 0.8x reducer/flattener. The first image is completely uncropped. There is still some distortion in the stars, particularly in the second image, but they look better than in 90% of my other images.

 

 

[Megawatt]

On 29/05/2024 at 05:42, kirkster501 said:

Flattener spacings are absolutely critical and the faster the scope the more critical it becomes.  Even a fraction of a millimeter is all it takes to ruin the star shapes.  Are you sure the flattener is at the exact distance recommended?  Are you using the WO flattener?  Does it do this at all temperatures?  Does it do it pointing at the Zenith?  Have you overtightened the scope mounting?  Are you over tightening the flattener?

On another note, tools such as Blur Xterminator make a superb job of correcting star shapes.

Yeah, I've been playing with the back spacing for years. I think whatever issue I'm having has made it harder to determine if my spacing is correct, because the stars are never round no matter what spacing I use. I'm using the exact recommended spacing now, but there is some debate on how "exact" that recommendation truly is. It astounds me how hard it is to find accurate information. You'd think there would be a published spec and that would be the end of it., but instead we have page after page of threads discussing what the published specs even mean. 

As for your other questions, these are all things I'm attempting to answer. So far, I haven't been able to say for sure that it has anything to do with the altitude angle or temperature. Focuser is centred and doesn't seem to sag at all. However, I'm beginning to suspect that my scope mounting is indeed overtightened, because when I loosened it I saw some immediate improvement (see my previous comment). More testing is required, but I appreciate your input. 

And you're absolutely correct that BlurX works miracles on star shapes, but I don't use Pixinsight and I haven't found any other program which can make any difference on my star shapes.

[Megawatt]

On 29/05/2024 at 10:22, Albir phil said:

Hi I have the same scope, I do however use the W O adjustable flattener/reducer, and never had any problem.So I agree best to use the dedicated F/R for the scope 

I'm using the dedicated reducer/flattener. If you are using the adjustable version, chances are you have the newer version of the GT81. Mine is first generation, I believe, which came out before adjustable flatteners were even available. 

[Stuart1971]

32 minutes ago, Megawatt said:

Well, if two different flatteners are giving the same poor result, it seems unlikely that a third flattener will provide a solution. 

One thing I did try it loosening the tube rings, and I don't want to get my hopes up but I do see an improvement. These were shot with the original William Optics 0.8x reducer/flattener. The first image is completely uncropped. There is still some distortion in the stars, particularly in the second image, but they look better than in 90% of my other images.

 

 

Yes but one of the flatteners you have tried is not the dedicated one, and that one could potentially be even worse…than the one that may or may not be at fault…

[Rallemikken]

On 12/05/2024 at 18:44, Earl said:

is something overtightened somewhere?

Exactly! And is anything sticking out in the lightcone? A screw, partly loose paint and such?