Plate solving failed

Using SharpCap's Polar Alignment feature
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Plate solving failed

Post by Christian » Fri Oct 04, 2019 7:19 am

I've read all your alignment notes, but until now SharpCap couldn't pass the plate solving step.
All attempts with different exposure times or gain were not successful.
I am using the SharpCap Version 3.2 64-bit with the CCD-Camera QHY5-III and a 200mm focal length photo lens.
After an upload of my files to "" the plate solving process were succsessfull. (see also my attachment)
I'm going to have one last test with a longer focal length. I hope this will help.....

Polar Alignement.jpg
Polar Alignement.jpg (491.64 KiB) Viewed 552 times

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Re: Plate solving failed

Post by admin » Fri Oct 04, 2019 5:50 pm


I think you may have overexposed your image. If you look in your screenshot at the bottom right hand side you can see that you have basically applied a reverse stretch in the mini histogram meaning that the image looks normal on screen in spite of the fact that most of the histogram points are well to the right of centre. I would suggest resetting the mini histogram stretch using the anticlockwise arrow button and then adjusting exposure and gain to ensure that you have a fairly dark background and stars showing. At that point hopefully the polar alignment routine will start to pick up some stars in the image and everything will start working.

Hope this helps, Robin

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Re: Plate solving failed

Post by chongo228 » Fri Oct 04, 2019 7:13 pm

@ Christian- It's been a while since I have used the polar alignment (my mount has been set up for a month now) but I do use the second party plate solve software (All sky plate solve) through SC. I believe what Robin said was correct about the histo. The size of the large star compared to the others tells me it's clipped far off the right side. I think you confirmed Robins idea as to why it fails when you said the online website solved it. The raw image you are downloading isn't stretched and the one on your screen is. Same file but displayed two different ways. Look up mini histogram in the documents

Also try this....I find that usually low gain (150 to 200) and 6 to 10 seconds work well with All sky to plate solve. I don't think the second party plate solvers use the display stretch....I think they get the raw image.
Raise the exposure and lower the gain. I find that gain of 200 and 6 - 8 seconds works well for me on a bright area like M31 and 12 seconds for a dark area like the Heart Nebula...but every setup is different. Around Polaris I'd think 5 to 8 seconds at 200 gain would get it....reset the mini histo first.

@ Robin.....does the polar align plate solve use the display stretch or the raw image?

Also, to get more info could about which stars it is (or isn't) detecting could you switch to live stack and watch the highlight detected stars/ number of stars found? Does the program use the same method of detecting stars for polar align and live stacking? 1500ms would be too short for would drop the next frame before it aligned but if his exposure was 3 or 4 seconds would this work to get more info?

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Re: Plate solving failed

Post by Christian » Sat Oct 05, 2019 6:40 pm

Hi Robin,

Thank you very much for your hints. You're right, the picture in my example was overexposed.
At the moment I'm waiting for good weather, then I'll do new tests. As soon as I have new results, I will get back to you.


@ chongo228
Thank you for your comments. Meanwhile I have read the topic of the histogram in the user manual again. I hope the next test is successful.

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