I am using a Celestron CGEMDX mount. I have followed the polar align script and get a supposed good alignment. When I go to Sirius the alignment is a couple of degrees off. I am trying to solve the problem. First question: How does Sharpcap get the time and latitude? Does it get it from the mount or from the internet? I am not connected to the internet at my location. The mount time and location is accurately.
Peter
Polar align plate solving does not give accurate results
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sedonapete
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Re: Polar align plate solving does not give accurate results
Hi,
the time, latitude and longitude only affect where the direction readouts (up/down/left/right) are correct - they do not affect the accuracy of the final alignment result if you manage to get the target star to the indicated position. That being said, time is taken from your computer clock and lat/long can be taken from your mount or entered manually (see the Plate Solving page in the Settings Dialog).
The first thing to do is to work through the troubleshooting steps listed here - http://www.sharpcap.co.uk/sharpcap/feat ... leshooting
The one that sounds relevant in your case is the 'I get the wrong results - SharpCap says my Polar Alignment is great after adjustment, but it isn't!' one - in particular check for any movement of the guidescope/camera as you rotate is this is by far the most common cause of poor results. You should make sure that you try the check of re-running the alignment process starting in the rotated position and moving back to the home position - that is a good check of whether the polar alignment is correct or not.
One more thing to note - bad gotos are *not* really a good test of polar alignment - they can come from other causes like cone error. A much better test of polar alignment accuracy is to measure drift using a program like PHD2.
cheers,
Robin
PS. If none of the above points you in the right direction, then please try to capture the following during a polar alignment run:
1) Screenshot and saved image (press snapshot button to save) in the home position
2) screenshot and saved image after rotating
3) screenshot and saved image after adjusting
4) SharpCap log file from this run of SharpCap
the time, latitude and longitude only affect where the direction readouts (up/down/left/right) are correct - they do not affect the accuracy of the final alignment result if you manage to get the target star to the indicated position. That being said, time is taken from your computer clock and lat/long can be taken from your mount or entered manually (see the Plate Solving page in the Settings Dialog).
The first thing to do is to work through the troubleshooting steps listed here - http://www.sharpcap.co.uk/sharpcap/feat ... leshooting
The one that sounds relevant in your case is the 'I get the wrong results - SharpCap says my Polar Alignment is great after adjustment, but it isn't!' one - in particular check for any movement of the guidescope/camera as you rotate is this is by far the most common cause of poor results. You should make sure that you try the check of re-running the alignment process starting in the rotated position and moving back to the home position - that is a good check of whether the polar alignment is correct or not.
One more thing to note - bad gotos are *not* really a good test of polar alignment - they can come from other causes like cone error. A much better test of polar alignment accuracy is to measure drift using a program like PHD2.
cheers,
Robin
PS. If none of the above points you in the right direction, then please try to capture the following during a polar alignment run:
1) Screenshot and saved image (press snapshot button to save) in the home position
2) screenshot and saved image after rotating
3) screenshot and saved image after adjusting
4) SharpCap log file from this run of SharpCap
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AussieHowie
- Posts: 25
- Joined: Fri Aug 11, 2017 12:23 am
Re: Polar align plate solving does not give accurate results
sedonapete ... you are following up the polar alignment with a 'normal' one, two, three, four star alignment aren't you?
Polar aligning just gets the ALT and AZ for the mount to be pointing right at the celestial poles ALT and AZ. Nothing else. It's internal object database which relies on RA and DEC will still be pointing any which way. Hence, after polar aligning, you have to do the 'normal' one, two, three, four or more star alignment in which you centre each star with the RA and DEC buttons as it is this which corrects its internal object databases RA and DEC coords to give you a more accurate GoTo.
Apologies if you know and are doing this.
If you are doing the correct Polar Alignment and then a 1, 2, 3, 4 etc star alignment and still finding objects degree's out of the field of view then it could be your camera being used to do the polar alignment has hot pixels which the plate solving is treating as stars - although this usually results in the plate solving not working. But I have had bad pixels give a poor alignment for me and I had to take a dark frame in SharpCap to fix it.
cheers and hope you find a solution.
Polar aligning just gets the ALT and AZ for the mount to be pointing right at the celestial poles ALT and AZ. Nothing else. It's internal object database which relies on RA and DEC will still be pointing any which way. Hence, after polar aligning, you have to do the 'normal' one, two, three, four or more star alignment in which you centre each star with the RA and DEC buttons as it is this which corrects its internal object databases RA and DEC coords to give you a more accurate GoTo.
Apologies if you know and are doing this.
If you are doing the correct Polar Alignment and then a 1, 2, 3, 4 etc star alignment and still finding objects degree's out of the field of view then it could be your camera being used to do the polar alignment has hot pixels which the plate solving is treating as stars - although this usually results in the plate solving not working. But I have had bad pixels give a poor alignment for me and I had to take a dark frame in SharpCap to fix it.
cheers and hope you find a solution.