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Polar align inconsistencies in ekos

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Hello,

I have been enjoying astrophotography for nearly a year now, but I am still trying to improve my guiding in PHD2, which is often above 1.5 arcsec for both RA and DEC (rms).

One of the factors might have something to do with poor polar alignment in Ekos*.

I polar align with my main scope, which is a C9.25, equipped with a QHY168C camera. My mount is an iOptron CEM40. I use OAG with an ASI 174mm mini.

I noticed there is almost always an inconsistency with my alignment. After the second or third iteration of PA following the installation of my mount in my backyard (on concrete stables) I usually manage to bring down the error to nearly 0.

However, if I start another alignment cycle, I usually get around 30", and sometimes nearly a minute, of error.

If I bring down this number again to 0 it will most likely swing back to 30" after the next iteration.

Therefore, I usually don't bother, but since I would like my guiding to improve, I thought this could be a good place to start, even though there are probably a thousand factors influencing the guiding process.

One possible culprit is that I do not lock the azimuth and the latitude screws after alignment.

As anyone encountered this inconsistency before?

Thanks!


* Even though PHD2 guiding assistant usually does not indicate a poor polar alignement.

EL
1 year 8 months ago #84542

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SCT are known to have mirror flop, that might affect the process. But frankly, 30" to 60" of polar error is quite acceptable. I would recommend tightening the adjustment bolts too and follow good balance practices, such as being east heavy. The closer you are to the weight limit or if you are over it, the more important balance becomes.
Finally, others have experienced less consistency with the routine through long focal lengths. They were better off using their guidescopes.
1 year 8 months ago #84557

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Hi Andrew,

Thanks for your reply.

My load is about 30 pounds and the CEM40 can tolerate up to 40 pounds.

My balancing is alright in RA, but I must say I have trouble balancing in DEC, as there appears to be a third axis for the center of gravity.

As for polar aligning with a guide scope, I could in fact use the small iguider which came with my CEM40 mount. Its focal length is too small to guide a C9.25 - and anyway I am using OAG -, but it should be sufficient for PA.

I am also going to lock the az and lat hex screws.

As far as guiding efficiency is concerned, these are certainly very good leads.

Thanks for the tips!
1 year 8 months ago #84562

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Hi Eric,

I have the CEM40 and would emphasise the need to tighten the alignment locking hex bolts. Do this after you have finished the adjustments but while the view is still refreshing. As you tighten the bolts do this in increments on either side rather than tightening up all at once on one side as you will see a shift in the polar alignment. Slow incremental tightening on the alt and az bolt should ensure that this can be excluded from the reasons that your mount is not guiding as well. You need to tighten the bolts quite a bit to ensure no movement with this mount.

I am using an OAG with a F6 refractor but your C9.25 is much longer than that so I would stick to OAG for guiding. The ipolar on the CEM40 is OK to polar align with but I have never used it as such and always do PA on the main scope. As Andrew says, the longer FL of the C9.25 may be an issue with PA as well. In which case try the ipolar :).

I routinely get 0.5-0.7 with the CEM40 using the EKOS internal guider . Don't forget to turn off PEC in the indi mount panel and handbox(if you use it) as this will interfere with guiding.

Hope this helps

Mike
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1 year 8 months ago #84568

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HI Spartacus,

Thanks for the tips.

I will try them this evening.

I will let you know about the results.

EL
1 year 8 months ago #84587

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Hi there,

Yesterday evening was quite clear and I could at last test the recommendations discussed herein.

I first tried to mount my iFinder scope only to find out I had no camera to use with it.

I know the scope came with a specific camera made by iOptron, but I just couldn’t find it.

I then tried to fit an ASI290MM mini into it (which I no longer used) but it didn’t work.

Therefore I abandoned the idea of using a small scope for polar alignment.

However, after locking the az and lat screws as much as I could, I managed to get a repeatability of about 30’’ for the PA, which I thought was well enough for PHD.

And in fact it did seem to improve my guiding since the average went from about 1.5’’ to 0.7’’, as you can see on the attached figure.

There are still some dirty spikes up to 2.2’’ on RA, but the average is not so bad, and I thought the result was acceptable, as you can see on the last figure.

So it looks like tightening the hex screws was a very good idea.

Thanks all for your help!

EL
Last edit: 1 year 8 months ago by Eric.
1 year 8 months ago #84768
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