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How to fix oval stars

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#1 jjaipa@yahoo.com

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Posted 02 June 2020 - 03:31 PM

Hi all, need some help trying to fix elongated stars. I have a link to an untouched light frame as well as PHD's Guiding Assistant results from 2 nights ago on google drive.

 

I was shooting at F10 and decided, due to NJ bortle 5 skies, to go to F7. I am guiding through an OAG with an additional .5 focal reducer to increase the FOV. The only way I try to determine if I have a good frame, is if the Pixinsight Eccentricity measure is less than .6. Only about 50%-60% of my frames are less than .6 Eccentricity so I think I can do better. 

 

Any help would be appreciated. 

 

Here's my setup:

Celestron Edge HD 11"

CGX-L Mount - Pier mount with Dan's Pier Plate

Imaging camera- ZWO ASI2600MC Pro. (Focal length 2,800 x .7 = 1,960mm)

Guiding: OAG - Zwo OAG with .5 Focal Reducer (Focal length of OAG 2,800 x .7 x .5 = 980mm)

Guiding camera: Zwo ASI294MC Pro

Filter drawer - ZWO

Filter Optolong L-ENHANCE FILTER - 2" 

 

Sequence Generator Pro

PHD2

Pixinsight

 

Untouched light frame 300seconds with L-eNhance filter

https://drive.google...iew?usp=sharing

 

PHD Guiding Assistant results:

https://drive.google...iew?usp=sharing

 

Thanks, Jim



#2 Peregrinatum

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Posted 02 June 2020 - 05:26 PM

the RA guiding error is much larger than the Dec... you would like them to be the same as much as possible, this causes oval stars...

 

one thing that helps for me is adjusting the frame rate in PHD2:

 

Dec > RA increase frame rate

RA > Dec decrease frame rate

 

So next time try to gradually decrease the frame rate to see if the RA error comes down closer to the Dec

 

Also, make sure you get a good calibration, calibrate on a star near the CE and the Meridian



#3 BQ Octantis

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Posted 02 June 2020 - 07:42 PM

A simple fix in post with Photoshop:

 

https://www.cloudyni...al-stars-round/

 

BQ



#4 APshooter

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Posted 02 June 2020 - 08:17 PM

Pixinsight has a tool for fixing that, under motion in one of the PSF's I think.



#5 jjaipa@yahoo.com

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Posted 02 June 2020 - 09:41 PM

I do calibrate on the CE & Meridian. I also did the drift alignment with CE & Meridian for alt az, then CE in the West for altitude. Really good video on this I found by Vanarchy in YouTube.

 

Although, I didn't think about the RA > Dec and frame rate. Is that exposure time? or is there a separate setting for frame rate in PHD2? 




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