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weird scatter plot

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#1 funkysandman

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Posted 07 September 2016 - 08:27 PM

Would anyone know how to interpret this scatter plot from PHD2?  

I'm trying to figure out why there are vertical lines with respect to RA.

 

setup is an AVX C8 SCT .63x reducer using OAG 

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  • weirdScatter.PNG


#2 Jon Rista

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Posted 07 September 2016 - 08:56 PM

Can you take a screenshot of your DEC plot as well? I assume the scatter is showing RA vertically, and DEC horizontally, yes? If so, then the answer to your question probably lies in the DEC axis, which would be the horizontal axis in the scatter plot, and the thing that was apparently getting "stuck" at the same locations repeatedly. 



#3 Goofi

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Posted 07 September 2016 - 09:12 PM

Any chance you were guiding on a double star?



#4 funkysandman

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Posted 07 September 2016 - 09:14 PM

Can you take a screenshot of your DEC plot as well? I assume the scatter is showing RA vertically, and DEC horizontally, yes? If so, then the answer to your question probably lies in the DEC axis, which would be the horizontal axis in the scatter plot, and the thing that was apparently getting "stuck" at the same locations repeatedly. 

The RA is on the horizontal x axis

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  • scatterDec.PNG


#5 funkysandman

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Posted 07 September 2016 - 09:18 PM

Any chance you were guiding on a double star?

doubt it..I've seen this on a bunch of my logs now..I'm wondering if it is a characteristic of my guide camera or mechanical mount issue.  My guide camera is an astro-video camera which uses ntsc and frame capture



#6 Jon Rista

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Posted 07 September 2016 - 10:34 PM

What is your guide camera? Isn't NTSC an interleaved field format? It's got two interleaved scanning fields on alternating cycles. I wonder if the frame interleaving might be resulting in funky star centroid calculations, resulting in the shifting of RA among several fixed locations. 


Edited by Jon Rista, 07 September 2016 - 10:35 PM.


#7 funkysandman

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Posted 08 September 2016 - 07:11 AM

You may be onto something there Jon - it is using an analog signal -perhaps this is where the pattern comes from?

This is the camera I am using:

 

http://www.astro-vid...dule-board.html


Edited by funkysandman, 08 September 2016 - 07:59 AM.


#8 Jon Rista

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Posted 08 September 2016 - 11:01 AM

Ok. From the specs for the sensor:

 

"This chip features a field period readout system and an electronic shutter with variable charge-storage time"

 

The sensor is definitely reading alternate fields independently. I would be willing to bet that is a part of the issue. Additionally, it seems it is color? I wonder if the oddball CFA might be affecting it as well, in combination with the alternative field reads. 



#9 funkysandman

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Posted 08 September 2016 - 11:55 AM

Ok. From the specs for the sensor:

 

"This chip features a field period readout system and an electronic shutter with variable charge-storage time"

 

The sensor is definitely reading alternate fields independently. I would be willing to bet that is a part of the issue. Additionally, it seems it is color? I wonder if the oddball CFA might be affecting it as well, in combination with the alternative field reads. 

yes, it is color.. I might have to get my hands on a better guide camera to rule out these issues..another test I think I could do would be to turn the camera 90 deg. and see if the pattern shows up in DEC


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#10 funkysandman

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Posted 08 September 2016 - 05:46 PM

I had recently rotated the camera, so I found a scatter plot from a month ago...the pattern is showing up in DEC!  must be the camera..i also suspect the guide star size impacts this too

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  • scatter3.PNG

Edited by funkysandman, 08 September 2016 - 05:48 PM.



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