Losing polar alignment?

Using SharpCap's Polar Alignment feature
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Croz
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Joined: Mon Jan 29, 2018 2:23 pm

Losing polar alignment?

Post by Croz » Mon Jan 29, 2018 2:42 pm

I'm hoping that someone can help me with an issue I've been having that could very well not be with the sharpcap software. I have a new AVX mount, and I have polar aligned it twice. Both times I seem to lose polar alignment. The first time I thought I had not tightened things down. But last night I had made sure the adjustment bolts were all locked down. My alignment through sharpcap was rated excellent. I then proceeded to do some testing with PhD2.

I'm just getting used to guiding, so I had been playing around for a while. In PhD it has a new guide assistant. I was noticing the polar error was quite high. So I went back to Sharpcap, and not only was I not aligned. But I couldn't even resolve in the first step of polar alignment.

Logic tells me that this has to be a physical issue, and bumping the mount would be the first question. At one point last night I had to unlock the clutches of the mount to bring it back to home position. Other than that I didn't touch it and I was pretty sure during that process that I did not move or bump it. Is unlocking the clutches a problem?

Anyone have any advice?

Thanks
Kevin

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admin
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Re: Losing polar alignment?

Post by admin » Mon Jan 29, 2018 7:45 pm

Yes, sounds like something moving/slipping/sinking (if you are using a tripod).

A good way to check your pointing is to get the mount into the home position and then snapshot a frame and upload to nova.astrometry.net and see where you are pointing. Try that at 10 minute intervals then see if anything is moving?

cheers,

Robin

robrj
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Joined: Fri Feb 17, 2017 1:03 am

Re: Losing polar alignment?

Post by robrj » Mon Jan 29, 2018 11:35 pm

You might also check the bolt that holds the mount head to the tripod (the bolt that runs through the leg separator). If it wasn't tightened enough, you might get some movement in the mount head as it slews.

frankieusn
Posts: 18
Joined: Fri Dec 22, 2017 9:30 pm

Re: Losing polar alignment?

Post by frankieusn » Wed Jan 31, 2018 3:23 am

I have the AVX. If you're using the included tripod you can forget about maintaining precise polar alignment from night to night. Each session will require realignment if you need it to be precise (think imaging). Walking nearby can change it particularly if its on a deck. Even breathing in the vicinity of the rig would throw it off. So many things can change it (dogs/cats/mosquito). Just for reference I have my AVX mounted on an 8" steel pier anchored to a 16" concrete base 38" in the ground protected inside my obsy and I still find polar alignment drifts from night to night ever so slightly. Typically in elevation due to the weight of equipment and temperature changes expanding and contracting the bolts. Not said to discourage. It's just a fact of life and should be part of your normal set up checks. Shouldn't take more than 5 minutes when you get the routine.

frankieusn
Posts: 18
Joined: Fri Dec 22, 2017 9:30 pm

Re: Losing polar alignment?

Post by frankieusn » Wed Jan 31, 2018 3:30 am

Also, yes unlocking the clutches and moving it by hand can very well shift the mount position around. I find the axis on the AVX to be still quite firm when unlocked so the pressure required to move it by hand could nudge your position on the tripod. One thing to keep in mind is that the tripod is most stable when the legs are fully retracted as low as you can go. The nobs that hold the legs in an elevated position can only be tightened so much because the legs are aluminium. It will also tend to wobble around when the legs are extended.

Croz
Posts: 2
Joined: Mon Jan 29, 2018 2:23 pm

Re: Losing polar alignment?

Post by Croz » Thu Feb 01, 2018 3:33 am

Thanks for all the replies. Gives me a few thing to try.

ChrisMoses
Posts: 1
Joined: Wed May 09, 2018 10:17 am

Re: Losing polar alignment?

Post by ChrisMoses » Wed May 09, 2018 10:36 am

Hi,
Did you find the cause? I'm experiencing the same thing.

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