Double Stars in my images... - Forums

Topic starter

Jul 24, 2021 · Edited: Jul 24, 2021

Hello.
I have a weird problem with my images.. Most of them have double stars... it seems that something is jumping but my guiding graph is good... last night i threw away 15 images out of 25..
it flex? or my mount? i don't know... some help here...
Here is some images with the problem...

zoom in :

my equipment is :
SW eq6r-Pro
SW esprit 100ed
Pegasus focus cube
ZWO ASI 183mm pro
im guiding with a 50mm guidscope with 180mm focal length and a asi 120mm..
PHD2 with multistar enabled...

phd log :
PHD2_GuideLog_2021-07-23_215144.txt

thanks for your answers!
Kostas.

Björn Arnold

Jul 24, 2021

Hi Kostas,

What exposure times did you have for your subs?

This is not flexure. Flexure leads to elongated stars but not double stars as flexure is a continuous smooth process over time. Something is jumping here.

I've taken a look at your phd2 log and unfortunately your guiding isn't good. Between the dithers, you have excessive RA error up to 3 arcsecs. It's also obvious that phd2 can't compensate the worm period.
What causes this? You may have play in the RA gear. For that you should give the RA a slight imbalance. Alternative the worm has some issue.

In general for the phd2 guiding I can recommend the PPEC algorithm for the RA axis.

CS
Björn

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Kostas Papageorgiou

Topic starter

Jul 24, 2021

Björn Arnold:
Hi Kostas,

What exposure times did you have for your subs?

This is not flexure. Flexure leads to elongated stars but not double stars as flexure is a continuous smooth process over time. Something is jumping here.

I've taken a look at your phd2 log and unfortunately your guiding isn't good. Between the dithers, you have excessive RA error up to 3 arcsecs. It's also obvious that phd2 can't compensate the worm period.
What causes this? You may have play in the RA gear. For that you should give the RA a slight imbalance. Alternative the worm has some issue.

In general for the phd2 guiding I can recommend the PPEC algorithm for the RA axis.

CS
Björn

thanks for your answer.
the exposure time is 300s .. i will try to imbalance and the PPEC training.. you mean this in settings ?

it was on hysteresis.. do i have to do PEC training on the mount?

Björn Arnold

Jul 24, 2021

Kostas Papageorgiou:
the exposure time is 300s .. i will try to imbalance and the PPEC training.. you mean this in settings ?

Yes, that setting. Start with the initial settings and see how it goes.
Re imbalance: it's only to compensate for possible gear play. Therefore, emphasis is on "slight" imbalance.

Kostas Papageorgiou:
it was on hysteresis.. do i have to do PEC training on the mount?

I've been using hysteresis quite some time on my CEM40 but I had sudden changes in the RA error. With the PPEC in PHD2 enabled, these were gone. Don't enable PEC in the mount. It might cause strange behavior, depending on the manufacturer. For my CEM40 it would be an issue if I'd turn it on in the mount.

Maybe another remark: for my taste, your guiding image scale is a bit large. I don't know the experience of others user with similar settings as yours. In my case, I have a guide scope with your parameters but a camera with 2.9um pixels which improves image scale by about 30%. But I wouldn't jump to the conclusion that this would be the culprit in your case. Even with the larger pixel scale, these peaks shouldn't appear.

Björn

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Kostas Papageorgiou

Topic starter

Jul 24, 2021

Now i get it. Thank you.
I'm having the same thoughts for the scale of my guide scope.. i have a zwo off axis but it was causing issues with focusing on different filters…

Rodrigo Roesch

Jul 24, 2021

Hello
Try to do some exposure without guiding and see if you have the double stars. If you do, it could be some debris in your gear. I have an Orion atlas mount and once in a while some debris from the housing falls into the gears and produce the jumps. If that is the case, you will have to open the mount and clean it.
hope this helps
Rodrigo

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Bob Lockwood

Jul 24, 2021

Rodrigo:
Try to do some exposure without guiding and see if you have the double stars. If you do, it could be some debris in your gear. I have an Orion atlas mount and once in a while some debris from the housing falls into the gears and produce the jumps. If that is the case, you will have to open the mount and clean it.

This is a good test to try, with and without guiding. This I believe would also show up on your guiding graph. I had an AP 900 mount and at one point in time, just watching the guiding graph, it would spike every 6:20 or one worm cycle. Ended up being what looked like a piece hair that the worm gear was running over every cycle. Removed the hair, issue went away. If you do see a spike in your guiding graph that’s not dither related, you may want to take a look at the RA assembly and see if there’s something that’s not suppose to be there.

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Ross Salinger

Jul 25, 2021

Usually when you get jumps like this in RA it's because something is sticking or dragging. It takes very very little pull on a guide scope or the mount to get this effect. You will not fix it by making adjustments in the gear mesh or in the PHD parameters.

Without seeing the rig, I'm just guessing but my guess is that you are not using an OTA mounted hub. If you use one of those then you can eliminate the nest of USB cables. The same thing can be done with a rig runner system - it acts like a power hub. If you use those two components then you only have 2 cables running from the system to the computer - one USB and one power.

That will fix this permanently.

Rgrds-Ross

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Kostas Papageorgiou

Topic starter

Jul 25, 2021

Hi
Last night I tried the Pec in PHD and imbalance my scope.
things went better...

Rodrigo:
Try to do some exposure without guiding and see if you have the double stars. If you do, it could be some debris in your gear.

I will try that... thanks

Bob Lockwood:
you may want to take a look at the RA assembly and see if there’s something that’s not suppose to be there

Im afraid to open the mount.. I hope it's not that!

Ross Salinger:
Usually when you get jumps like this in RA it's because something is sticking or dragging. It takes very very little pull on a guide scope or the mount to get this effect. You will not fix it by making adjustments in the gear mesh or in the PHD parameters.

Without seeing the rig, I'm just guessing but my guess is that you are not using an OTA mounted hub. If you use one of those then you can eliminate the nest of USB cables.

I don't use an OTA mounted hub and all my cables are hanging around...
I could try some cable management...

Thank you for answers. You helping me alot!