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Anyone know what causes this?

Acquisition Guiding Deep Sky
8 replies•457 views
Jerry Gerber avatar
Jerry Gerber avatar
The first sub of the evening has elongated stars, every sub thereafter is fine.   Same thing happened last night the first sub had stars that looked like there's a guiding problem, but every sub after that has stars that look round. 

Should I put a 5 or 10 second pause in NINA after plate solving and before imaging to resolve this?

Thanks!
Jerry
Tony Gondola avatar
Tony Gondola avatar
If it's a scope settling problem then yes. That or just cull your first sub.
dayglow avatar
dayglow avatar
I always program a short dummy shot to be the first after slewing to a new target because my old mount had both DEC and RA play.  For my mount, I found 10 seconds to be adequate to eliminate this problem.

The first image after meridian flip would sometimes also exhibit some elongation but I had no means of inserting a dummy at that point.
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LookSpaceThings avatar
LookSpaceThings avatar
Sometime the guider takes a bit of time to adjust even after the calibration. Did you check the graphs on PHD2?
Lynn K avatar
Lynn K avatar
I see a similar issue with when dithering.  If no delay is set on start of sequence, the sequence will dither and start exposure without  settling.  This will cause streaked stars in the 1st sub. The additional subs have a dithering settling period before starting exposure.

Lynn K.
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Jerry Gerber avatar
Jerry Gerber avatar
These are unguided, the 10MicronGM1000 mount does fine without guiding at 1000mm focal length under Bortle 1-2 skies.
I'll insert a 10 second delay between Solve & Sync and starting the image run…
Brian Diaz avatar
Brian Diaz avatar
hi

take a look at this article

https://www.astropix.com/html/astrophotography/diagnosing_trailed_stars.html

maybe help you 

CS
Brian
Jerry Gerber avatar
Jerry Gerber avatar
Brian Diaz:
hi

take a look at this article

https://www.astropix.com/html/astrophotography/diagnosing_trailed_stars.html

maybe help you 

CS
Brian

Thanks Brian, I read the article it's very helpful and well-written.
Clayton Ostler avatar
Clayton Ostler avatar
My guess is your guiding and/or mount has not settled. 

Troubleshooting, 
1. Check that guiding as settled, recalibrated and started successfully before starting to image
2. Have you recalibrated guiding for each session?