Alt drifts when making az adjustments and vice versa

Using SharpCap's Polar Alignment feature
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edwardko
Posts: 3
Joined: Mon Jul 16, 2018 9:13 pm

Alt drifts when making az adjustments and vice versa

Post by edwardko » Mon Jul 16, 2018 9:27 pm

Hi All

I am a newbie coming to terms with PA. I live in surburbia Melbourne and have no chance of seeing Octans in my backyard. I have therefore "splashed" out on a budget 50mm guidescope + ASI120MC (equivalent) camera to do PA using Sharpcap.

I have managed to get plate solve going and find that I am down by a couple of degrees and left by a couple of degrees.

I proceed to adjust Alt and got that to about 30" and started to adjust the Az. As I bring the Az error down, I find that my Alt error increase again. When I get the Az error to say 30", and adjust the Alt error down, the Az error moves.

It is as if the mount is not level, even though the spirit indicator says it is.

Any ideas anyone?
Thanks

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admin
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Re: Alt drifts when making az adjustments and vice versa

Post by admin » Tue Jul 17, 2018 7:31 pm

Hi,

there are two possible causes for this

1) SharpCap has got a poor estimate of your longitude from your time zone and is therefore not managing to convert RA/Dec co-ordinates into Altitude and Azimuth correctly. If you are using SharpCap 3.1 then you can set your Lat/Long for polar alignment in the settings and that should correct this type of issue.

2) This can also arise from physical deficincies of the Alt/Az adjustment system of the mount - for instance NEQ6 mounts show this sort of problem when you get close that tweaking one direction will affect the other. One technique is to make the final adjustments only by tightening the threads (ie even without untightening the opposite thread, an extra tweak on one of the adjusters will move the mount a small amount). Also remember that getting closer than 30" is not really required.

cheers,

Robin

edwardko
Posts: 3
Joined: Mon Jul 16, 2018 9:13 pm

Re: Alt drifts when making az adjustments and vice versa

Post by edwardko » Tue Jul 17, 2018 9:03 pm

Thanks Robin

I will give that a try. By the way I am using a Star Adventurer.

Regards Edward

edwardko
Posts: 3
Joined: Mon Jul 16, 2018 9:13 pm

Re: Alt drifts when making az adjustments and vice versa

Post by edwardko » Tue Jul 17, 2018 9:04 pm

Thanks Robin

I will give that a try. By the way I am using a Star Adventurer.

Regards Edward

robrj
Posts: 62
Joined: Fri Feb 17, 2017 1:03 am

Re: Alt drifts when making az adjustments and vice versa

Post by robrj » Tue Jul 17, 2018 9:13 pm

I experience this as well with my AVX. For me the solution was to adjust until one reading is about half the other and then switch. So for example, if Alt and Az both showed 4, I would adjust Alt to 2 and then adjust Az and repeat as necessary. If the were vastly different, for example, Alt 8 and Az 3, I adjust the one that's out the most first. For the final tweak, I used Robin's method of just tightening the tension to edge it in.

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