Re: Eggy Stars with Polar Axis Correction
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Nathan Myhrvold
If pincushion or barrel distortion is a major factor in plate solving accuracy then I would expect the results to be OTA dependent. Some scopes have more or less distortion than others.
This could explain why some people don't see a difference in modeling with different plate solvers.
A way to test this would be to collect a set (ideally like 100) images. Since you only need enough exposure for the stars, so this would not take long. The images could then be batch solved with various plate solvers.
Doing this for different OTA would help determine the role of distortion. It would also help compare plate solving software.
I am sure there are other accuracy factors too besides distortion.
Ray's email says he has seen 2 arcsec variation between plate solvers. A test suite of images will help quantify this for a specific set up.
I will do this when my scope arrives (planewave DR 350, on order). It is f/3 so likely does have some distortion - but other scopes would differ.
The images could be shot in the same positions used for making a pointing model or dec arc model. Indeed you just save images while making the models.
Batch plate solving the images would allow comparison of plate sloved solutions but it does not determine which, if any of them, are correct. One could us astrometry.net as a reference, i suppose.
But what we would really like to know is - do the differences yield noticably different models? And if they do, which is better? That might be hard to do....
One metric of quality would be model fit from APCC. I don't know if it will accept a batch of stored images however. That would be a convenient way for testing one point solver after another with consistent input (ie the same images).
Ray, suppose I had a take such images, can I retrieve the encoder positions for each?
Nathan
Going mobile
From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Dean Jacobsen via groups.io <deanjacobsen@...>
Sent: Saturday, July 23, 2022 10:45:35 AM To: main@ap-gto.groups.io <main@ap-gto.groups.io> Subject: [EXTERNAL] Re: [ap-gto] Mach2 and Eggy Stars with Polar Axis Correction Thanks. That is certainly a reason to invest in PinPoint. I was never able to get Image Link to work for me when I was setting up my imaging software a couple of years ago. I am still using Plate Solve 2. It has been working fine for me. And if it
isn’t broke…
-- Dean Jacobsen Astrobin Image Gallery - https://www.astrobin.com/users/deanjacobsen/ |
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