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Need help with star streaking

astrophotography SCT dslr
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#1 mostvisited

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Posted 23 May 2020 - 02:46 PM

Hello Everyone,

Recently I got a brand new CGEM II mount and have been trying to do 5 minute long exposures. My OTA is a Celestron 8SE with 6.3 reducer and I autoguide it with PHD2 +  orion startshoot autoguider + mini guidescope. Imaging camera is a modified T4i.

 

In all of my photos I am seeing a weird streaking pattern. Left and right upper corners seems to have streaks in opposite directions while lower left is kinda straight. I did east heavy balancing and  a fair polar alignment using polar drift align tool. Not sure if it is differential flexure or issue with the OTA / Mount.   Hope other experience folks here could guide me in right direction. Attached is a 1.5 hours of stacked image stretched in pixinsight and corresponding PHD logs. 

 

 

Thanks,

VA

 

 

 

 

 

Attached Files



#2 mostvisited

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Posted 23 May 2020 - 02:47 PM

Here is the stacked image.

 

bode_cigar.png



#3 Tapio

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Posted 23 May 2020 - 02:57 PM

To me it looks like some rotational error.
Anyway I think mini guidescope is not good enough for that scope.
Consider switching to OAG.
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#4 mostvisited

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Posted 23 May 2020 - 03:14 PM

To me it looks like some rotational error.
Anyway I think mini guidescope is not good enough for that scope.
Consider switching to OAG.

 

Yep, I also felt its kind of rotational error. To my understanding it is usually related to bad polar alignment. Mine was not perfect for sure but not bad either. What else could cause rotational error like that ?

I have ordered a Celestron OAG and gonna try it again. However I am wondering if flexure would cause similar streaks in all photos. At least one out of 20 should be better or different :)




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