Eggy Stars

[TrevorW]

I ran ASTAP aberration check on a number of single frames. they show tilt to be under 8% This figure varied between different subs on different targets but was fairly consistent, showing virtually none so what may be causing my egg shaped stars ??



Attached single frame

[Dave882 (David)]

Looks like a backspacing issue to me…

[TrevorW]

David heres the thing how do I check that ??


I focus on a star using a mask etc, set up QHy268c 10" GSO RC with Moonlite focuser



my image train is focuser extension tube filter situated around 50mm from camera sensor in adapter,

[Dave882 (David)]

Originally Posted by TrevorW

David hers the thing how do I check that ??


I focus on a star using a mask etc, set up QHy268c 10" GSO RC with Moonlite focuser



my image train is focuser extension tube filter situated around 50mm from camera sensor in adapter,

Well just from my own experience with similar stars using my scts I’ve made use of small spacer rings from 0.1-2mm. By adding and subtracting I got to a point where they stars were reasonable in 2 or 3 corners. Then I tried to tackle tilt to resolve the final corner, and then final tweak in backspacing if necessary.
It’s amazing how much of a difference 0.1mm can make!!

[gb44 (Glenn)]

Also have a quick check of the dovetail space with a micrometer too. Just in case tilt has been introduced when you've assembled/disassembled the thing. Its very possible to introduce a huge tilt.

Cheers
GlennB

[TrevorW]

thanks will check that

[Nikolas (Nik)]

If you are using a filter in the imaging train add a 1mm spacer as this looks like a backspace issue where it needs just a little more space by the look of the pattern

[TrevorW]

A number of options to try, I could also remove the filter to do some tests before after etc to see if that is causing the issue. Also recheck collimation, PA, focus. One thing I've not been able to achieve is these magical FHD, figures people often quote.

[xelasnave]

Hi Trevor

Have a look at this and as they say watch until the end.

https://youtu.be/N60vzaIZq6Y

Alex

[TrevorW]

Thanks Alex put it in perspective suburban skies are not going to produce magical figures especially imaging at f/8

[ChrisV (Chris)]

What sort of scope is it?
Also looks like camera tilt as the egginess varies across the corners. But start by roughly getting backspacing correct

[TrevorW]

Gso 10" f/8 truss rc

[Joshua Bunn (Joshua)]

Looks like your camera sensor is too close, which is inline with adding a filter in the image train.

[gregbradley]

Its tilt. Doesn't matter what your software says. Perhaps its telling what the average is as half the image is good.

Right side is good. Bottom left starting to go off and top right is poor.

If it were spacing it would be all the stars not just corners.

Greg.

[atalas]

I believe Greg is correct and also when you evaluate things the focus needs to be perfect.