Weird star shape in live stack

[nexusjeep]

Hi Robin,
Thanks for the update sorry to have caused the stress but at least I know it's not my refractor . Not sure if it would make any difference but is this more likely to show the better Polar Alignment is as on the night for the data you have my polar alignment total error was between 0 and 1 arc second and the rotational history carried on flat along the horizontal axis for the full 7hr + imaging session.

Cheers
Nick

[admin]

Hi Nick,

OK, now I have this worked out properly... The alignment was working properly for the typical sort of deformations you see (rotation, offset) and also for uniform scaling, but anything a bit beyond that (non-uniform scaling, skew, etc) was not being handled properly, even though the calculations were detecting those sorts of things. It has always been like that, but because in most cases rotation and offset are all that you get, you don't notice the problem much (phew!). It took me a lot of checking and testing before I finally found the tiny error in the code that meant that information was being lost.

I think a combination of good sharp stars in the sub images and perhaps a bit of lens distortion has made the effect show up in your dataset. I now have a fix for this, so watch out for the next update.

Finding this is (looking back on it...) a good thing, as even in cases where the effect is not obvious, the fix should lead to slightly tighter stars in the stack.

cheers,

Robin

[nexusjeep]

Hi Robin,
Glad you found a solution for it will wait with excitement for the update although that will probably mean it will rain for the next month .

Cheers
Nick