Teardrop Star Issues

[Stuart1971]

29 minutes ago, ollypenrice said:

But they can be round, as I explained earlier: in order to elongate a star, the guide error has to be more than half the image scale, or thereabouts. If pixels were dimensionless points this would not be true but pixels have a dimension capable of absorbing a small but significant degree of error. This tolerance diminishes as the image scale increases in resolution, which is why you need better guiding to image at finer pixels scales.

I'd also want to think about the shape of the elongation. It is spindle-shaped, ie pointed at each end and thicker in the middle. In many years of imaging I have never seen guide error produce that shape and I'm struggling to think of a guiding error scenario which could produce it.

The killer indicator, though, is that the elongations are not parallel across the chip. That absolutely rules out tracking error.

Olly

Edit: I 'crossed in the post' with Wim who has put a numerical value of 0.8 arcsecs on the RMS below which guiding will have no effect and with Stuart whose experiences match my own.

 

I always aim for at least half of my 1.72”/pixel imaging scale as a goal for my RMS, but my issue is OCD, or more the fight against it taking over,  to get it as low as possible, even though it makes absolutely no difference to the final image, and the more I tell myself.. “It’s fine at 0.6 or 0.7 RMS, the more I get the urge to get it lower….

The joys of being OCD…😂😂

[michael8554]

16 hours ago, gorann said:

I think this was already pointed out but here it is again: I just calculated the pixel scale of his set-up, and it  is 1.61"/pixel, so any guiding error in any direction less that 0.8"/pixel could never be seen in the image. So guiding error is totally exluded here.

Gorann to the rescue !

I hadn't registerd that the RA and Dec deviations were smaller than the 1.6arcsec/pixel image scale.

Now I know 😆

Michael

[Stuart1971]

1 minute ago, michael8554 said:

Gorann to the rescue !

I hadn't registerd that the RA and Dec deviations were smaller than the 1.6arcsec/pixel image scale.

Now I know 😆

Michael

Like Goran Said, it had already been pointed out several times before…..😉👍🏼

[michael8554]

Okay, thanks to whomever said it first !

Michael