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Polar alignment Skyguider pro with Ipolar

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#1 Maged

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Posted 22 February 2020 - 07:46 AM

Hello,

I have a question regarding accurate polar alignment of the skyguider pro using ipolar. I perfectly align the mount and after I find and frame my target I notice from the ipolar app that my alignment is a little off.
At first I thought this is because little vibration during framing of the target but I avoided that with very light touches and still I am not correctly aligned.

My question here is do I have to re-align again after locating my target? Any tips on polar alignment for a newbie?

Also for skyguider pro with ipolar users, how long exposure time could you achieve for your light frames?

Thanks and clear skies

#2 ThatsMyCoffee

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Posted 22 February 2020 - 08:30 AM

It should be good for the night.  I'd re-calibrate it.  Something is wrong.

 

Mine does change after loading the OTA.  But if I do that first, it's good.

 

Any chance you're on soft ground and the mount is moving?  And the ipolar is securly/properly mounted?



#3 Maged

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Posted 22 February 2020 - 11:28 AM

The ipolar already came installed with the mount and I am using the William optics wedge for the skyguider pro.

I recalibrated it like twice. I still can’t narrow down what I may be doing wrong.

I thought about the Tripod as it is not the best of quality but the bubble indicator shows that the tripod is leveled.

Edited by Maged, 22 February 2020 - 11:29 AM.


#4 ajaxuk

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Posted 22 February 2020 - 04:11 PM

It is possible that the polar scope is not aligned perfectly with the RA axis. You can check this, first get a good PA and then rotate the RA axis 90 degrees left and / or to the right to see if the crosshair has moved on the iPolar app. How far off does the crosshair move in your case?

 

You can also check the PA with other software, I use the SharpCap pro routine.

 

I have managed to get up to 3 minute exposures but 2 minutes is generally more consistent. 


Edited by ajaxuk, 22 February 2020 - 04:13 PM.


#5 TelescopeGreg

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Posted 22 February 2020 - 07:52 PM

Polar alignment and Star alignment are separate things.  Either could be off...



#6 Maged

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Posted 23 February 2020 - 07:16 AM

It is possible that the polar scope is not aligned perfectly with the RA axis. You can check this, first get a good PA and then rotate the RA axis 90 degrees left and / or to the right to see if the crosshair has moved on the iPolar app. How far off does the crosshair move in your case?

 

You can also check the PA with other software, I use the SharpCap pro routine.

 

I have managed to get up to 3 minute exposures but 2 minutes is generally more consistent. 

I will double check that. Thanks.



#7 Maged

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Posted 23 February 2020 - 07:17 AM

Polar alignment and Star alignment are separate things.  Either could be off...

Can you please explain more, and how both can be corrected?

thanks to you



#8 TelescopeGreg

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Posted 24 February 2020 - 01:47 AM

Can you please explain more, and how both can be corrected?

thanks to you

What I was referring to is that these two forms of alignment are totally different things.  But, my apologies...  I hadn't done my research, and had assumed that you had a GoTo mount.  The star alignment doesn't apply to your mount unless you're using a GoTo hand controller or such.

 

So, Polar Alignment is the mechanical alignment of the RA axis of an Equatorial mount to be exactly in line with the Earth's axis of rotation.  In other words, so that it points to the North (or South) Celestial Pole.  This makes it possible for the mount to track the sky as the Earth spins, by spinning the other way to cancel out the motion.  If it's not exactly aligned, your stars will start to drift.  This isn't something you do relative to the imaging target; it's usually done by aiming at the NCP, or some where close.

 

Once that alignment is done, don't touch those mechanical knobs!  Anywhere you aim the camera, your target should remain steady.  Are you using a GoTo hand controller or planetarium software, or just aiming the camera yourself?  If so, that controller or software needs to know where things are in the sky, because the camera's axis may not be exactly the same as the mount's, and being even slightly out of level will cause an offset in the sky.  Both of these need to be accounted for by whatever means you're using for aiming the camera.  That's what I was referring to by a star alignment.  But again, once the polar alignment is done, it's done.  Changing targets shouldn't have any effect on the polar alignment.


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#9 Maged

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Posted 24 February 2020 - 03:47 AM

What I was referring to is that these two forms of alignment are totally different things.  But, my apologies...  I hadn't done my research, and had assumed that you had a GoTo mount.  The star alignment doesn't apply to your mount unless you're using a GoTo hand controller or such.

 

So, Polar Alignment is the mechanical alignment of the RA axis of an Equatorial mount to be exactly in line with the Earth's axis of rotation.  In other words, so that it points to the North (or South) Celestial Pole.  This makes it possible for the mount to track the sky as the Earth spins, by spinning the other way to cancel out the motion.  If it's not exactly aligned, your stars will start to drift.  This isn't something you do relative to the imaging target; it's usually done by aiming at the NCP, or some where close.

 

Once that alignment is done, don't touch those mechanical knobs!  Anywhere you aim the camera, your target should remain steady.  Are you using a GoTo hand controller or planetarium software, or just aiming the camera yourself?  If so, that controller or software needs to know where things are in the sky, because the camera's axis may not be exactly the same as the mount's, and being even slightly out of level will cause an offset in the sky.  Both of these need to be accounted for by whatever means you're using for aiming the camera.  That's what I was referring to by a star alignment.  But again, once the polar alignment is done, it's done.  Changing targets shouldn't have any effect on the polar alignment.

Thanks, yes in my case I don't have a go-to function so I can't star align. My setup is so simple so I cannot connect it to planetarium software, I have to locate and frame the target manually.  

 

My problem here is the polar alignment is messed up a little once I locate and frame the target so I am trying to narrow down the reasons to avoid polar alignment at the beginning of the session and polar alignment again with each target.



#10 TelescopeGreg

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Posted 24 February 2020 - 03:23 PM

Thanks, yes in my case I don't have a go-to function so I can't star align. My setup is so simple so I cannot connect it to planetarium software, I have to locate and frame the target manually.  

 

My problem here is the polar alignment is messed up a little once I locate and frame the target so I am trying to narrow down the reasons to avoid polar alignment at the beginning of the session and polar alignment again with each target.

Ok, that's sort of what I was thinking you were thinking.  Polar alignment, at least on every other equatorial mount I've heard talked about (including Alt/Az mounts on a wedge), is done once and only once, as the first thing you do in setting things up.  It's a mechanical alignment of the RA axis to that of the Earth's spin, and that RA bearing's axis of rotation doesn't change when you slew the scope from target to target.  Use the Ipolar tool and get it as absolutely close as you can, then leave the mechanics locked.  Unless you have a massively huge mount, the Earth's axis of rotation isn't going to change :), so neither should your scope's.

 

If the polar alignment is actually changing, then something is moving or bending that shouldn't be.


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#11 Sonya6500

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Posted 25 February 2020 - 09:07 PM

I just got my Ipolar installed in my SGP.  I do my alignment with the scope and camera installed. I epoxied steel washers to my driveway so my mount is always in the same position. I used a digital level from work to get it set up in the beginning. I don't always hook up the laptop now because the alignment is pretty much dead on. I am happy with two minute exposures with no trailing using the Astrotech 72 or Z61. I don't guide and am happy with my results.




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