Stars deformation - Forums

Topic starter

Aug 9, 2022 · Edited: Aug 9, 2022

Hello all,

Since I have my EQ6R Pro (3 months) on all my subs I have deformed stars. They're all in the same direction, I conclude that there is a guiding problem. But my process before shooting is as follow if I consider only parameters which can impact the guiding:
Bad Polar align: I do PA with Asiair Plus and I reach all the time less than 10" of error
Bad balancing: I know he is good
No AutoGuiding system: My future purchase
The last thing is Periodic Error. But for 60s of Exposure time .... the periodic error should be really out of tolerances ?

If someone has idea ...

General acquisition parameters:
ASI204MC Pro + L-eXtrem - SW200/1000
TS Optics Coma Corrector Maxfield 0.95x
Sub = 60s

I include the 3 parts of my last picture where the problem is really visible (3 corners)

Steve Solon

Aug 9, 2022

Hi Maxime,
Since you are using a coma corrector, and all the stars are affected, guiding error seems the logical answer. Depending on the telescope used, collimation could also be a factor.
- - Steve

Maxime Martin

Topic starter

Aug 9, 2022

Hello, thanks.
But the I respect the 55mm of backfocus. If a problem about coma, stars should point the center of the picture right ?
THe collimation is also good, I check everytime before shooting combining Cheshire and laser.

I think it's guiding error but for 60s of exposure time …. When I had NEQ5 i shooted during 60s with no problem like that that why i'm questionning

Christian Großmann

Aug 9, 2022

Hi Maxime,

I realized this in some of my images, too. The nights when I took them were really cold (about -15 to -20 degrees) and my EQ6-R had surely trouble to move correctly. At those temperatures, nothing moved freely. It turned out, that I had a problem with flexure. It seems, that is your problem, too. Are you using a guide scope on top of everything? There could be a problem with that. The stars looked exactly the same as yours.

In my case, I only realized this during those cold nights. Otherwise, everything seems to be ok. I solved this issue by placing the guide scope on the Newton I use down to near the mount. This way, there was less bending of the parts involved and it worked quite well. Better would be an OAG, but that's not always needed.

It could also be, that your guide scope is not aligned well with your main scope. If it is off quite a bit, there could be those kind of issues, too. I don't think it is a problem of your mount.

That is only a guess and a thing that is easy to fix. At least it's worth a try.

CS

Christian

Helpful Supportive

Christian Großmann

Aug 9, 2022

Maxime Martin:
Hello, thanks.
But the I respect the 55mm of backfocus. If a problem about coma, stars should point the center of the picture right ?
THe collimation is also good, I check everytime before shooting combining Cheshire and laser.

I think it's guiding error but for 60s of exposure time .... When I had NEQ5 i shooted during 60s with no problem like that that why i'm questionning

Sorry, I did not read all of your comments first. But I still think that felxure is a possible solution. Please check your EQ6 for loose parts. Try to use an allen wrench to check if every screw is tight (be careful on the smaller screws, cause they adjust some things). Maybe the base plate is a tiny bit loose and the scope can move a bit.

Maxime Martin

Topic starter

Aug 9, 2022

Hello Christian,

Thanks for your answer.
This picture has been took last week-end with a ambiant temperature equal to 10-15 during the night.
I d'ont have a guide scope.
I will check about the flexion on the optical path, maybe this is the problem, but I don't have tilt on my picture ;) But I don't know how to measure the flexion if there is one …

Christian Großmann

Aug 9, 2022 · Edited: Aug 9, 2022

Ahhh! These small details everywhere… sorry for missing this info.

But we are talking about a 1000mm focal length. That is really long for an unguided mount. Because of the tolerances in the mechanics, the motors, the different system designs (belt vs. gear), etc between the mounts you use, there could be small differences in the speed of the RA axis. You are using a camera with a really small sensor and you are basically cropping the usable field of view from the scope and use only a small portion of it. Personally I would say, that for your current equipment the results are very good. Your problems will be non existent if you are using a guide scope.

You are using an ASI 294MC, didn't you? Then your sensor is not that small…

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Lynn K

Aug 11, 2022

I agree with Christian. At that focal length, 60 min exposure will produce streaked stars. I suppect that if you image near polaris the stars will improve, and near the maridian at DEC 0 they will be worst. You need to auto guide for the type of imaging you are attempting to do. You then will be able to achieve round stars and longer exposures.

Lynn K.

Helpful Concise

Alicia Rossiter

Aug 11, 2022

Fully agree, with that focal length there is no way to get good results without guiding
You should try to do shorter exposures and/or even try BIN 2 x 2
I also recommend to check the collimation. With that long focal length, a very minor collimation correction makes a BIG difference

Clear skies,
Alicia

Helpful

Chase Newtson

Aug 11, 2022

Since you are not guiding, you mention your balance is good, but try having your balance oh so slightly East heavy. This may help keep everything locked in and have (hopefully) no back lash.

But in the end, Autoguide.

Hope you find the solution,

Chase

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