Guiding issues or something else? - Forums

Topic starter

Jun 17, 2025 · Edited: Jun 17, 2025

Hi all,

Yesterday I finally assembled my setup after 2 months - nice feeling to be with rig again

Unfortunately the real night here starts only at 23:00, so it's quite though to do all normal tweaking of the setup. After the normal setup (polar alignment - using PHD2 drift alignment, guiding - PHD2 - calibration, focusing, ...) I started acquisition and quickly noticed the image/flatness is not good. The pattern was quite obvious (see below)

I am using the petzval Takahashi FSQ106edx so I don't think it's the back-focus issue. Initially I thought it might be the tilt of the imaging train (I am having ZWO OAG, ZWO FW and ZWO asi294mm connected), but now I am thinking it might be incorrect guiding.

Another info: January this year I had accident with my mount that I partially fixed, but I still have some issues when doing meridian flip, that is also the reason I am suspecting the guiding / polar alignment (I did it facing west but then slew to the east side). Guiding numbers were quite OK (0.5-0.6" RMS) but I know this doesn't mean anything for the star shapes.
I would also like to mention that usually in the same assembly I have image with stars being nice in all corners.

As the night comes so late, I'd like to be ready with all the ideas for tonight, so I'd really appreciate any ideas/feedback from the forum. I will try of course with shorter shots to try to get eliminate guiding, I will also try to rotate image to see the effect. But of course any other ideas will be appreciated

All filters (R, G and B) shows the same pattern, below image is 180 seconds R acquisition.

Aberration inspector from PixInsight:

ASTAP shows the pattern of the stars quite obviously the pattern how the stars are prolong - it seems the 'center' is right-middle and the stars are 'circulating' around - this is also why I started to think it could be polar alignment / guiding issue:

andrea tasselli

Frequent contributor

Jun 17, 2025 · Edited: Jun 17, 2025

Very bad PA, you have image rotation and that cannot be fixed by any kind of guiding. Don't do (ever) PHD PA. Get SharpCap and use its polar alignment routine instead. (you will have to buy the Pro version I think but it is very cheap). This can't fail unless you have serious hardware issues with the mount (sagging tripod, creeping altitude bolts and such). And don't complain too much about the short night, cause you are lucky seeing from here. Here there isn't any till the 27th of July and nautical twilight starts at 23:45 and ends at 2:15!

Jure Menart

Topic starter

Jun 17, 2025 · Edited: Jun 17, 2025

andrea tasselli:
Very bad PA, you have image rotation and that cannot be fixed by any kind a guiding. Don't do (ever) PHD PA. Get SharpCap and use its polar alignment routine instead. (you will have to buy the Pro version I think but it is very cheap). This can't fail unless you have serious hardware issues with the mount (sagging tripod, creeping altitude bolts and such). And don't complain too much about the short night, cause you are lucky seeing from here. Here there isn't any till the 27th of July and nautical twilight starts at 23:45 and ends at 2:15!

Thanks Andrea,

You confirmed my suspicion about PA, i just phrased it incorrectly in original post. I will try out the SharpCap for PA.

I do have some issues with my mount that still need to be resolved. But this is story for another time

CS,
Jure

Médéric Hébert

Jun 17, 2025

+1 for very bad PA, we can see the field rotation in the images you provided.

If you don't want to spend money on Sharpcap, the Nina pluggin "Three Point Polar Alignment" works great too.

Jure Menart

Topic starter

Jun 17, 2025

Médéric Hébert:
+1 for very bad PA, we can see the field rotation in the images you provided.

If you don't want to spend money on Sharpcap, the Nina pluggin "Three Point Polar Alignment" works great too.

Hi Mederic

Thanks for confirmation. I fully agree, wanted to double check with others so I am not as surprised in the middle of the night

TiffsAndAstro

Jun 17, 2025

Jure Menart:
Médéric Hébert:
+1 for very bad PA, we can see the field rotation in the images you provided.

If you don't want to spend money on Sharpcap, the Nina pluggin "Three Point Polar Alignment" works great too.

Hi Mederic

Thanks for confirmation. I fully agree, wanted to double check with others so I am not as surprised in the middle of the night

Can use sharpcap free to confirm a polar alignment btw

Michael Maas

Jun 17, 2025

I use the QHY PoleMaster Electronic Polar Alignment Scope to do my alignments, its fast and accurate. I think it cost $300.

Michael

Jure Menart

Topic starter

Jun 17, 2025

Michael Maas:
I use the QHY PoleMaster Electronic Polar Alignment Scope to do my alignments, its fast and accurate. I think it cost $300.

Michael

You need to see Polaris for that right?

In my previous garden I didn't see it, so I just started to use PHD drift alignment. Now I do see it but I am just so used to do it like that, that I never transitioned

Maybe it's time now - this happened yesterday first time, but it's always good to take these kind of situations as an opportunity to improve

Michael Maas

Jun 17, 2025

yes, you need to see Polaris and the stars surrounding it. The PoleMaster provides an image of Polaris and the surrounding area, you identify Polaris and then rotate the mound in RA in 3 steps of about 30 degrees. Then you return to the starting position and PoleMaster tells you where Polaris should be in the image if you where PA aligned, you move it there with the RA and Declination knobs on your mount and then you are all set. You can also monitor it for awhile to see that there is little PA drift.

Hope this helps

Michale

Helpful

bigCatAstro

Jun 17, 2025

Médéric Hébert:
+1 for very bad PA, we can see the field rotation in the images you provided.

If you don't want to spend money on Sharpcap, the Nina pluggin "Three Point Polar Alignment" works great too.

Yes, TPPA works great and I appreciate that it works without needing a view of Polaris.

Well Written

Mark Fox

Jun 17, 2025

What target is this? Sorry, I can't plate solve with my eyes….

The reason that I ask is that I did some quick math on the image streaks. The focus of rotation does look to be somewhere near the right frame edge, as you have mentioned. A little trigonometry indicates that the length of the star streaks appears to be the amount of sky rotation over 2.5-3 minutes, around that focal point of your image. So, for example, if you were acquiring images around Polaris/NP, it is almost as if the mount was not tracking at all.

It just seems odd that a bad PA would show that kind of rotation if not imaging near the NP.

FWIW.

CS,
Mark

Well Written Helpful Insightful Engaging Supportive

Jure Menart

Topic starter

Jun 17, 2025

Mark Fox:
What target is this? Sorry, I can't plate solve with my eyes....

The reason that I ask is that I did some quick math on the image streaks. The focus of rotation does look to be somewhere near the right frame edge, as you have mentioned. A little trigonometry indicates that the length of the star streaks appears to be the amount of sky rotation over 2.5-3 minutes, around that focal point of your image. So, for example, if you were acquiring images around Polaris/NP, it is almost as if the mount was not tracking at all.

It just seems odd that a bad PA would show that kind of rotation if not imaging near the NP.

FWIW.

CS,
Mark

Hi Mark,

It's not near Polaris - it's Seahorse nebula.

CS,
Jure

Mark Fox

Jun 17, 2025

Thanks for the clarification, Jure.

If the target were more distance from the pole, the severity of the rotation couldn't be explained only by bad PA. But the Seahorse is 'way up there' and I suppose I could buy in to the PA issue. Of course, the other posters here have significant experience, much more than I. Would a bad PA really cause that kind of variation in star streaks, such that it clearly rotates around a point with a rotation point located within the frame?

Respectful Supportive

Riccardo Civati

Jun 17, 2025

@Jure Menart i suggest you to use sharp cap pro for PA, i had a PA with this program in my observatory and now i am below 10 arcsec error. with my encodeer mount i don't need autoguide.
Ricccardo

andrea tasselli

Frequent contributor

Jun 17, 2025

Mark Fox:
Thanks for the clarification, Jure.

If the target were more distance from the pole, the severity of the rotation couldn't be explained only by bad PA. But the Seahorse is 'way up there' and I suppose I could buy in to the PA issue. Of course, the other posters here have significant experience, much more than I. Would a bad PA really cause that kind of variation in star streaks, such that it clearly rotates around a point with a rotation point located within the frame?

Yes.