Star shapes

[recceranger]

Hi folks,

I have been testing my new setup; ASIAIR Plus, WO Z61 and ZWOASI533 over the past few weeks. On looking closely at all the photos of different DSO over different nights I have noticed a familiar pattern in the star shapes across the entire frame/FoV. It's as though my guiding is off slightly, but read out on the guide graph is telling me I'm good.  I am using dithering function when guiding and have noticed when I have been flicking through the FITS files that the image shift on the dithered frames is always in the same direction (to the right of frame). This is in line with how the stars seem to be trailing ever so slightly. Could dithering cause this? Or, could it be an issue with camera/scope?

I have provided a couple of images (single FITS images) of both the Heart and Rosette Nebula to give a visual example of the issue. Any advice suggestions appreciated.

[almcl]

Unlikely to be dithering, as that should be taking place when the imaging camera is not taking pictures and also should be in random directions.  

Not sure what your set up is but if the RA and Dec oscillations are similar and you are using a guidescope  it could be flexure. 

Hard to tell from the x4 reduced pngs, but the Rosette doesn't look as bad as the Heart?

Edited February 8, 2022 by almcl

[recceranger]

8 minutes ago, almcl said:

Unlikely to be dithering, as that should be taking place when the imaging camera is not taking pictures and also should be in random directions.  

Not sure what your set up is but if the RA and Dec oscillations are similar and you are using a guidescope  it could be flexure. 

Hard to tell from the x4 reduced pngs, but the Rosette doesn't look as bad as the Heart?

Yeh, it is better and I'm wondering if it is to do with the scope/mount orientation? The heart nebula was around 40% and ESE of the meridian. The Heart Nebula was almost directly overhead. I think I'll do a few shorter exposures of around 30 secs etc, just to rule out any issues with the optics. It certainly seems more likely to be a guiding issue. 

[recceranger]

Just now, recceranger said:

Yeh, it is better and I'm wondering if it is to do with the scope/mount orientation? The heart nebula was around 40% and ESE of the meridian. The Heart Nebula was almost directly overhead. I think I'll do a few shorter exposures of around 30 secs etc, just to rule out any issues with the optics. It certainly seems more likely to be a guiding issue. 

Let me rephrase! The Rosette Nebula was around 40% ESE!

[almcl]

What does PHD2 report the oscillations as? 

Your AZEQ6 mount is capable of guiding at around .6" (or at least my 6 year old one is) and you are imaging at 2.15 " per px so even in moderate seeing should produce OK stars?