Newbie- Help with image processing

DrGiga

Member
Aug 7, 2020
9
1
Hi All,
I am new to this hobby. I have a SC8 with Hyperstar on a AVX mount. My subframes seem fine but after stacking I get all these line defects but stars seem fine. . I would appreciate if you can help me to find what is the reason.
Thanks
Newbie

Here is the image after stacking and background extraction, neutralization and multi scale linear transform

1596823889750.png
Here is the subframe
1596824413467.png
Here is after stacking.
1596824490524.png
 

DrGiga

Member
Aug 7, 2020
9
1
Srecaldin, Thank you for your reply. dithering was on. in SGP, I set Dither to Medium every two frames.
 

pfile

PTeam Member
Nov 23, 2009
5,603
102
really does look like no dithering. if you load all the unregistered subs into blink, do you see the stars jumping around? if instead the stars just march along a diagonal line then dithering did not work.

also from the look of it the subexposures are too short. and were the subs calibrated at all?

rob
 

DrGiga

Member
Aug 7, 2020
9
1
Rob, Thank you for advice. I checked in Blink. stars jumping around in very small steps but in some frames there are large diagonal jumping of stars. Maybe I have set something wrong.
Should I set dither for every frame in SGP? then it takes 10S to settle down. I use Hyperstar with F=1.9 and take 60S subs. I was worried that it is already too long. Image statistic shows the median value about 8000. I heard that median value should be about 900 -1200.
Anyway, AVX mount will lead to elongated stars with 120S( guided). Finally, Is there a way to get rid of these lines in PixInsight?
Thanks
 

pfile

PTeam Member
Nov 23, 2009
5,603
102
well large jumps are ok, it's just that if when the subs are loaded in the order they were acquired (which might not happen with blink unless your filenames are correct) if it's like a movie of the stars continuously moving in one direction, then there was no dithering (and you are looking at differential flexure between your guide camera and imaging camera.)

did you calibrate these frames? if you get rid of any and all hot pixels thru calibration (or if that doesn't completely eliminate them, CosmeticCorrection) then you shouldn't have such pronounced streaks. also if you set up the pixel rejection properly in ImageIntegration, they should be rejected during stacking anyway.

rob
 

John_Gill

Well-known member
May 6, 2016
443
11
62
Durban, South Africa
... as a side note, on the AVX mount, you can tighten-up the Dec and RA motors slightly (check you-tube for details) and you will get 120-180 second exposures.

John
 

DrGiga

Member
Aug 7, 2020
9
1
All,
Thank you for taking your time and help me out.
@Rob, I calibrated subs. ( super bias, master dark and master flat) and did cosmetic correction. ( Auto detect Hot sigma& cold sigma)
Here is my image integration setting. pixel rejection 2&3 are default
1597081009809.png
Here are my calibration files ASI 183MC,
Master dark ( T=-10C, t=60S, Gain=270)
1597079309858.png


Master flat ( T=-10C, t=0S in SGP, Gain=270)
1597079565951.png
Master Bias ( T=-10C, t=0S in SGP, Gain=270)
1597079642919.png
super bias
1597079741218.png

@ John,
I decided to get a G11. It will arrive on this Friday. Therefore, I am not going to tune the AVX.
@Gerald,
Thank you for providing information about collimation. I am too afraid to touch Hyperstar screws. I think first I need to learn if I have an issue with collimation then I follow your instructions. Thank you again for advice. I attached my calibration files. my master dark was taken at the same exposure length and temperature as my light files.
 

pfile

PTeam Member
Nov 23, 2009
5,603
102
just fyi i would skip local normalization when you are just getting started. it requires pretty careful tuning and an understanding of the process which you won't have when starting out.

because you have amp glows there's no point in dark optimization which means there's no point in using a master bias or superbias. you can try calibrating with just the master dark and master flat (separately calibrated of course) and make sure dark optimization is turned off.
 

ngc1535

PTeam Member
Feb 1, 2014
521
63
AdamBlockStudios.com
just fyi i would skip local normalization when you are just getting started. it requires pretty careful tuning and an understanding of the process which you won't have when starting out.

because you have amp glows there's no point in dark optimization which means there's no point in using a master bias or superbias. you can try calibrating with just the master dark and master flat (separately calibrated of course) and make sure dark optimization is turned off.
It is very good to see this advice being promoted!
Good stuff.
-adam
 

DrGiga

Member
Aug 7, 2020
9
1
All,
Once more thanks to all who provided feedback. Few days back I got 120S subs with hyperstar and made sure that Dithering is on.. I still have problem with flat and when I add it then there are many hot pixels that I can not remove them by cosmetic correction. So I did not use flats.
Here is the Andromeda picture after brief processing with PI.
Alex
1597517988339.png
 
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DrGiga

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Aug 7, 2020
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