SharpCap Polar Alignment with PHD2 complaint.

Using SharpCap's Polar Alignment feature
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stephen2615
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Joined: Sat Mar 09, 2019 11:10 pm

SharpCap Polar Alignment with PHD2 complaint.

#1

Post by stephen2615 »

Greetings everyone.

I have a problem that just could be my stupidity.

I use SharpCap to do polar alignment (PA) using a small guide scope and camera (ZWO ASI 120MC-S with a 30F4). That system is superfluous (from my Star Adventurer days) so I thought it would be good at PA given its seemingly good results. I can easily get excellent status from SharpCap but PHD2 says my PA is horrible. It keeps complaining about it. I am getting PA errors from PHD2 of more than 30 arc minutes but SharpCap said PA is excellent.

PHD2 uses a Everwin 60mm guide scope (220 mm focal length) and a ZWO ASI 290 MM Mini. I haven't tried SharpCap PA using the Everwin scope but would it be a better system for PA given guiding would use the same gear? Guiding sometimes goes pear shaped for no apparent reason and some of my subs looks like I have PA errors.

Any advice would be most welcome.

Stephen
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oopfan
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Re: SharpCap Polar Alignment with PHD2 complaint.

#2

Post by oopfan »

Hi Stephen,

I too had the same problem. It turned out that I did not adequately lock the altitude of the polar axis after PA.

Brian
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admin
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Re: SharpCap Polar Alignment with PHD2 complaint.

#3

Post by admin »

Hi,

did you find and check out the polar alignment troubleshooting checklist? https://www.sharpcap.co.uk/sharpcap/fea ... leshooting

The most common cause of bad alignment when SharpCap says it is good is if something is shifting as you rotate the telescope around the RA axis - for instance if the guide scope or camera are able to flex relative to the mount axis. The troubleshooting page explains this in more detail, including how to check for the problem.

cheers,

Robin
stephen2615
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Joined: Sat Mar 09, 2019 11:10 pm

Re: SharpCap Polar Alignment with PHD2 complaint.

#4

Post by stephen2615 »

oopfan wrote: Wed Jun 30, 2021 10:28 am Hi Stephen,

I too had the same problem. It turned out that I did not adequately lock the altitude of the polar axis after PA.

Brian
Hi Brian,

Thanks. That's interesting. I tend to not adjust the front altitude thread all that much. I generally only adjust the back thread and don't play much with the front one unless I have to loosen it for some major adjustment at the back and that doesn't happen all that much. Screwing the front down will often change things so I leave it where it normally is which is not really tight. I expected it was something that I did that was just dumb. Now to wait another few weeks to get a clear night again to test that out.

Stephen
stephen2615
Posts: 21
Joined: Sat Mar 09, 2019 11:10 pm

Re: SharpCap Polar Alignment with PHD2 complaint.

#5

Post by stephen2615 »

admin wrote: Wed Jun 30, 2021 1:01 pm Hi,

did you find and check out the polar alignment troubleshooting checklist? https://www.sharpcap.co.uk/sharpcap/fea ... leshooting

The most common cause of bad alignment when SharpCap says it is good is if something is shifting as you rotate the telescope around the RA axis - for instance if the guide scope or camera are able to flex relative to the mount axis. The troubleshooting page explains this in more detail, including how to check for the problem.

cheers,

Robin
Hi Robin,

Thanks for taking the time to respond. I had an issue a while back with differential flexing with my guide scope but that is now sorted out. I will review your checklist and see if anything springs to mind.

Regards

Stephen
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oopfan
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Re: SharpCap Polar Alignment with PHD2 complaint.

#6

Post by oopfan »

Hi Stephen,

Thanks for the up-vote. May I ask, how long do you let the Guiding Assistant run? I give mine a full turn of the worm gear which is about 500 seconds. Even when I have excellent PA, the assistant initially says that it is off by several arc-minutes. It takes a few minutes for it to converge.

Brian
stephen2615
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Joined: Sat Mar 09, 2019 11:10 pm

Re: SharpCap Polar Alignment with PHD2 complaint.

#7

Post by stephen2615 »

Hi Brian,

Around four mins to get past the 3 min PHD2 recommendation. I have always had a strange difference in PHDs PA measure but it has tripled in recent days. The weather forecast is bleak so it is going to take time to test your suggestion. I have bit the bullet and bought a bigger mount as I want a bigger scope. I want to nail down my eccentricity issues.
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Re: SharpCap Polar Alignment with PHD2 complaint.

#8

Post by oopfan »

Hi Stephen,

We are in the same boat with respect to weather. It's been nearly 2 weeks for me.

Here are the 3 things that greatly improved my PA and Guiding:
1. Cable Management. I made a video here: https://rumble.com/vheku9-brians-astrop ... ement.html
2. Glued the guide scope's dovetail shoe to the anchor point on the main scope.
3. Tightened the polar axis' altitude bolt after PA.

Brian
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