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Follow the Bouncing Bubble


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I was once told in passing not to trust the OEM bubble level on equipment.  It was a long time ago, and not really related to astronomical equipment.

HOWEVER, it apparently applies to just about anything and ESPECIALLY astronomical equipment.  Ever since I bought my new mount, I have had issues with guiding and less than spectacular results with plate solving tracking to a target.  If I fiddled with it enough, it would work in a "barely acceptable" fashion.  I tried everything I could think of (even some really stupid ideas).  My only clue was that polar alignment with a polar scope to perfection did not lead to good polar alignment being reported properly elsewhere in the sky.  PHD Guiding Assistant, for example, would always report up to 300 arcmin off for polar alignment once I left the pole.  Other software that did not use the mount camera also reported similarly bad polar alignment. 

When I did a polar alignment with software that used the main imaging scope, rather than the polar scope, the result in PHD away from the pole was also bad.  Not identical, but still very bad.  For a while I considered that my mount was just a dud.

The attached picture shows the problem.  Prior to actually checking with a level, I had always meticulously leveled the mount with the OEM bubble level.  Long story short, once I started leveling the mount with an actual working level, everything began working as advertised.  It kills me to think of how many hours and imaging nights I wasted chasing such a simple problem.

May this post help prevent duplication of my ineptitude in this matter.

 

FlawInIOPTRONGEM28.png

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Happy to be shot down here but I think I have learned that this degree of accuracy in level is not required. I plonk my tripod down, check the bubble is central-ish and polar align. As long as that is done correctly all should be fine. Lots of other things to go wrong, that is true, but no need to worry about this bit from what I have seen.....

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5 minutes ago, scotty38 said:

Happy to be shot down here but I think I have learned that this degree of accuracy in level is not required. I plonk my tripod down, check the bubble is central-ish and polar align. As long as that is done correctly all should be fine. Lots of other things to go wrong, that is true, but no need to worry about this bit from what I have seen.....

Correct, it makes no difference at all if the mount is level, as that’s what PA corrects, close is good, but that’s all you need…no point in spending time on getting an EQ mount perfectly level….many people just do not realise this….👍🏼

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19 hours ago, JonCarleton said:

I was once told in passing not to trust the OEM bubble level on equipment.  It was a long time ago, and not really related to astronomical equipment.

HOWEVER, it apparently applies to just about anything and ESPECIALLY astronomical equipment.  Ever since I bought my new mount, I have had issues with guiding and less than spectacular results with plate solving tracking to a target.  If I fiddled with it enough, it would work in a "barely acceptable" fashion.  I tried everything I could think of (even some really stupid ideas).  My only clue was that polar alignment with a polar scope to perfection did not lead to good polar alignment being reported properly elsewhere in the sky.  PHD Guiding Assistant, for example, would always report up to 300 arcmin off for polar alignment once I left the pole.  Other software that did not use the mount camera also reported similarly bad polar alignment. 

When I did a polar alignment with software that used the main imaging scope, rather than the polar scope, the result in PHD away from the pole was also bad.  Not identical, but still very bad.  For a while I considered that my mount was just a dud.

The attached picture shows the problem.  Prior to actually checking with a level, I had always meticulously leveled the mount with the OEM bubble level.  Long story short, once I started leveling the mount with an actual working level, everything began working as advertised.  It kills me to think of how many hours and imaging nights I wasted chasing such a simple problem.

May this post help prevent duplication of my ineptitude in this matter.

 

FlawInIOPTRONGEM28.png

No need for it to be level, close is good enough, PA does the rest….don’t sweat over it….👍🏼

Edited by Stuart1971
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Just think of a polar axis shaft perfectly aligned but on its own suspended in space.  You could then place everything around it, mount, tripod, pier  randomly within reason and it would make no difference to the accuracy.    🙂

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I also believe what has been said above about tripod levelling not mattering is true (and I don't bother to level mine).

However, what perplexes me is the reported phd2 polar alignment error - 300 arcmins is 10x full moon widths(!); that's a significant distance from the pole, despite OP specifying that very accurate polar alignment was done. Anyone have any ideas about this? 

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5 minutes ago, The Lazy Astronomer said:

I also believe what has been said above about tripod levelling not mattering is true (and I don't bother to level mine).

However, what perplexes me is the reported phd2 polar alignment error - 300 arcmins is 10x full moon widths(!); that's a significant distance from the pole, despite OP specifying that very accurate polar alignment was done. Anyone have any ideas about this? 

Well... Not sure what the issues were but I was assuming the guiding issues were down to something other than being level....

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Posted (edited)

My guiding graphs always looked like an earthquake monitor during an volcano eruption.  After leveling the base and doing the alignment with the integral polar scope, not only does my alignment match exactly the result in PHD2 drift alignment (using the main scope), my graph now looks like the patient died.  In this case, a happy result.

While you are correct about a -proper- polar alignment correcting an off-level mount, In my case, the lack of a level mount fouled up the calibration of iPolar, which became the root cause of my perpetual misalignment.  After leveling the mount, the re-calibration of iPolar yielded very reliable results.  A detail I should have explained in the initial post.

Edited by JonCarleton
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1 hour ago, The Lazy Astronomer said:

I also believe what has been said above about tripod levelling not mattering is true (and I don't bother to level mine).

However, what perplexes me is the reported phd2 polar alignment error - 300 arcmins is 10x full moon widths(!); that's a significant distance from the pole, despite OP specifying that very accurate polar alignment was done. Anyone have any ideas about this? 

The PA algorithm in PHD2 is pretty much useless, it just does not work at all, so this should be ignored. I ran guiding assistant two nights ago, twice in pretty much succession, in very close parts of the sky and got 3 arc mins error the first time. And 14.7 the second….it’s just a waste of time taking any notice of it….in Sharpcap I am approx 2 arc mins off the NCP…so the figure above don’t surprise me….

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3 hours ago, Stuart1971 said:

The PA algorithm in PHD2 is pretty much useless, it just does not work at all, so this should be ignored. I ran guiding assistant two nights ago, twice in pretty much succession, in very close parts of the sky and got 3 arc mins error the first time. And 14.7 the second….it’s just a waste of time taking any notice of it….in Sharpcap I am approx 2 arc mins off the NCP…so the figure above don’t surprise me….

My experience is that the guiding assistant is usually within a couple of minutes of the Sharpcap figure - I tend not to pay attention to it either as l trust Sharpcap (minimal DEC guiding corrections back that up), but I certainly wouldn't say  the phd2 figure was a waste of time.

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23 minutes ago, The Lazy Astronomer said:

My experience is that the guiding assistant is usually within a couple of minutes of the Sharpcap figure - I tend not to pay attention to it either as l trust Sharpcap (minimal DEC guiding corrections back that up), but I certainly wouldn't say  the phd2 figure was a waste of time.

The PA figure is, well in my experience anyway, also read it in another forum, but if it works for you….👍🏼

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Posted (edited)

Actually, (being allergic to Windoze) I typically run CCDCiel in Linux.  It was the guiding routine in CCDCiel (using the main scope) that put me back right. 

I have also had very little help or useful information from PHD2 Guiding Assistant, but used it as an example (though I did try it).  I think the drift alignment tool is probably reasonably OK, if you have all night to run it.  Interestingly enough, with a good polar align, PHD2 Guiding Assistant doesn't bark quite as loud as it once did.

Edited by JonCarleton
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