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Oakley Matt
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Joined: Sat Jun 05, 2021 7:40 am

Hi

#1

Post by Oakley Matt »

I’m PRETTY new to astrophotography in an overall sense. I’m currently trying to expand my knowledge to begin capturing DSO’S.

I have a Celestron 8” SCT.

A few nights back I wanted to practise polar aligning by using Sharpcap, which after some faffing around was able to do.

A few nights later I wanted to try Plate Solving with Sharpcap. I got the following error - 'Failed to read xylist field'.

I went out again last night and got exactly the same error. On both nights of trying.

Any ideas why this please?
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admin
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Re: Hi

#2

Post by admin »

Hi,

it could mean that there are no stars being found in the image by the plate solving application - a google search for the error message shows that it happens sometimes on the online astrometry.net server for images that look completely dark:

https://www.google.com/search?q="failed ... list+field"

If you look in the SharpCap log, you should see some messages from the plate solving engine before the error happens - probably something like this

Code: Select all

Info   	12:05:32.108260	#1 	Plate solving : Extracting sources...																					
Info   	12:05:32.219984	#1 	Plate solving : simplexy: found 20 sources.			
If you are getting no sources found (or less than about 15-20) then there is definitely a problem with star detection. Things you can try are

* Make the stars brighter - increase gain and/or exposure, and make sure that you have the display stretch set to default (no stretch) - otherwise the stretch can make the stars look visible to you on screen, but they will not be picked up by the plate solver.
* Reduce the value of the sigma parameter in the plate solving settings -this makes it more sensitive to faint stars.

hope this helps,

Robin
Oakley Matt
Posts: 5
Joined: Sat Jun 05, 2021 7:40 am

Re: Hi

#3

Post by Oakley Matt »

Hi Robin,

Yes thanks. Someone else suggested it was possibly an exposure issue. I cant remember my exposure settings for when I previously polar aligned, but this other person suggested trying a 10 second exposure, I know with my previous experience it was nowhere near that. So thats the next step.


Thankyou.
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oopfan
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Re: Hi

#4

Post by oopfan »

Hi Matt,

I thought I'd add my two cents.

I have this perennial problem of not being able to plate solve in or near the constellation of Cygnus. It just runs and runs and runs. Several minutes go by, and finally failure.

I decided to debug it offline with the Deep-Sky Camera in SharpCap. It turns out that the Gamma setting was 5. For NGC 6888, it literally found over 300 stars. Through experimentation I discovered that plate solving can fail two ways: TOO MANY stars and TOO FEW stars. Having around 100 stars was a good amount. I had to raise the Gamma setting to about 80.

I experimented with version 3.2 and 3.1. They have similar behavior, but I prefer 3.1. The message that tells me the number of star's found stays on the screen long enough for me to read, whereas in 3.2 the message goes by so quickly that I need to be extremely alert or else I miss it.

Brian
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