PA issue

Using SharpCap's Polar Alignment feature
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Chuck
Posts: 14
Joined: Mon May 14, 2018 12:07 pm

PA issue

Post by Chuck » Mon May 14, 2018 6:04 pm

I was having an issue last night .......SharpCap would not solve after detecting a quite suitable number of stars and indicating it was using 15 of them. It even would report the green....."Plate Solving Ready..." message. To ensure that I am within 5 degrees of the north Celestial Pole I use EQMOD'S polar alignment tool.....very quick, very easy...Polaris was on the circle so I know I met that requirement. It's very confusing because it's not like sharpcap was unable to detect Enough stars...it clearly was because it was reporting that it was. Thanks for any help.

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admin
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Re: PA issue

Post by admin » Mon May 14, 2018 8:42 pm

Hi,

the first thought I have is that perhaps your guide scope is misaligned with the mount by quite a (relatively) big angle - in that case your mount could be polar aligned but the guide scope could be pointing more than 5 degrees away from the pole, which would give the symptoms you describe.

The best thing to do is to capture a frame or two that SharpCap is having problems solving and then share them here and I can look into it. My first step in these cases is to upload the frames to http://nova.astrometry.net/ and plate solve them to see where they are really pointing and the field of view.

cheers,

Robin

Chuck
Posts: 14
Joined: Mon May 14, 2018 12:07 pm

Re: PA issue

Post by Chuck » Tue May 15, 2018 9:01 pm

Thanks for the reply. My guide scope was mounted quite well, I have to say. I had better luck last night after adjusting the guide scope focus..... is it possible for the software to detect a suitable number of stars and indicate using 15 of them but yet they are still a bit out of focus to solve?

It solved in the park position fairly easily last night, but after rotating through 90° to the east it took quite a while. I don't understand how it can solve one frame and then fail to solve the next 20 then solve again then fail to solve several more, and on and on this way...... since you can't see your progress until after a solved frame, it can take quite a while when it's behaving that way.

I will look into uploading those frames as you suggest, thank you.

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admin
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Re: PA issue

Post by admin » Tue May 15, 2018 9:15 pm

Hi,

depending on exact pointing and alignment, the star fields for the two positions can be different and sometimes you get a nice rich field in one position that solves easily and a very faint field in the other position that causes issues. The tricks you can use in that case are

1) start with the mount in the 'difficult to solve' position - that lets you tweak the star detection parameters for that field of view to get it working, then it should work easily when you rotate back to the easy position

2) try different positions - for example 45 degrees left of home to 45 degrees right of home. It's the rotation between the positions that matters.

cheers,

Robin

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