"ZigZag" Hot Pixels

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brenski
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"ZigZag" Hot Pixels

#1

Post by brenski »


Hi I'm hopeful someone will have come across this phenomenon before and can tell me how to fix it.

♦ Zwo ASI 183MC Pro (cooled) ♦ Skywatcher Evostar 72ED DS-Pro ♦ SW Star Adv Pro 2i ♦ Optolong UHC LPF 2" ♦ Stellamira Field Flattener / 0.8 Reducer

♦ Lights are 30s 150gain (x60)
♦ Darks are 30s 150gain (x15)

Some information:
♦ "zigzags" are appearing on my first stacked images after Sharpcap capture - immediately after preliminary Black-Level adjustment in PShop (ie before any real processing)
♦ Zigzags are all over the image (crop below is from lower right centre of Orion nebula)
♦ No matter which method I use to apply darks: as Master Dark subtractions in Sharpcap or as Darks in DSS or "noise" files in Sequator - these zigzags still appear.

What am I doing wrong? Any help appreciated, thanks

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Juno16 United States of America
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Re: "ZigZag" Hot Pixels

#2

Post by Juno16 »


Wow. That is strange!

I wish that I could help, but I've not seen that before. Strange that each artifact has the same pattern!

Looking forward to replies.
Jim

Scopes: Explore Scientific ED102 APO, Sharpstar 61 EDPH II APO, Samyang 135 F2 (still on the Nikon).
Mount: Skywatcher HEQ5 Pro with Rowan Belt Mod
Stuff: ASI EAF Focus Motor (x2), Orion 50mm Guide Scope, ZWO 30 mm Guide Scope, ASI 220mm min, ASI 120mm mini, Stellarview 0.8 FR/FF, Sharpstar 0.8 FR/FF, Mele Overloock 3C.
Camera/Filters/Software: ASI 533 mc pro, ASI 120mm mini, Orion SSAG, IDAS LPS D-1, Optolong L-Enhance, ZWO UV/IR Cut, N.I.N.A., Green Swamp Server, PHD2, Adobe Photoshop CC, Pixinsight.
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Re: "ZigZag" Hot Pixels

#3

Post by brenski »


Juno16 wrote: Wed Feb 08, 2023 12:24 pm Wow. That is strange!

I wish that I could help, but I've not seen that before. Strange that each artifact has the same pattern!

Looking forward to replies.
yep. I'm thinking it's an alignment error?
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yobbo89 Australia
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Re: "ZigZag" Hot Pixels

#4

Post by yobbo89 »


umm hot pixel rejection not selected in stacking with dithering enabled on the imaging/tracking software ? , it's a very strange dither pattern though
scopes :gso/bintel f4 12"truss tube, bresser messier ar127s /skywatcher 10'' dob,meade 12'' f10 lx200 sct
cameras : asi 1600mm-c/asi1600mm-c,asi120mc,prostar lp guidecam, nikkon d60, sony a7,asi 290 mm
mounts : eq6 pro/eq8/mesu 200 v2
filters : 2'' astronomik lp/badder lrgb h-a,sII,oIII,h-b,Baader Solar Continuum, chroma 3nm ha,sii,oiii,nii,rgb,lowglow,uv/ir,Thousand Oaks Solar Filter,1.25'' #47 violet,pro planet 742 ir,pro planet 807 ir,pro planet 642 bp ir.
extras : skywatcher f4 aplanatic cc, Baader MPCC MKIII Coma Corrector,Orion Field Flattener,zwo 1.25''adc.starlight maxi 2" 9x filter wheel,tele vue 2x barlow .

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Re: "ZigZag" Hot Pixels

#5

Post by brenski »


yobbo89 wrote: Wed Feb 08, 2023 12:42 pm umm hot pixel rejection not selected in stacking with dithering enabled on the imaging/tracking software ? , it's a very strange dither pattern though
thanks, would you happen to know where I can find that in Deep Sky Stacker ?
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yobbo89 Australia
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Re: "ZigZag" Hot Pixels

#6

Post by yobbo89 »


brenski wrote: Wed Feb 08, 2023 12:45 pm
yobbo89 wrote: Wed Feb 08, 2023 12:42 pm umm hot pixel rejection not selected in stacking with dithering enabled on the imaging/tracking software ? , it's a very strange dither pattern though
thanks, would you happen to know where I can find that in Deep Sky Stacker ?
it's been awhile since i've process an image ,usually just dithering alone should remove the hot pixels and then stacking in deepsky stacker,

so i click on stack check pictures , (it should have all the exposure times in this window) then look for stacking parameters at the bottom, then click on light , i use kappa-sigma clipping,hit ok.

along that menu there is a cosmetic tab, theres an additonal post hot pixel removal option that i havn't used yet or know how to .

when you register check pictures a popup should have a window with 3 tick boxes, click on automatic detection of hot pixels .


also make sure you have current up to date dark frames, that might help .
scopes :gso/bintel f4 12"truss tube, bresser messier ar127s /skywatcher 10'' dob,meade 12'' f10 lx200 sct
cameras : asi 1600mm-c/asi1600mm-c,asi120mc,prostar lp guidecam, nikkon d60, sony a7,asi 290 mm
mounts : eq6 pro/eq8/mesu 200 v2
filters : 2'' astronomik lp/badder lrgb h-a,sII,oIII,h-b,Baader Solar Continuum, chroma 3nm ha,sii,oiii,nii,rgb,lowglow,uv/ir,Thousand Oaks Solar Filter,1.25'' #47 violet,pro planet 742 ir,pro planet 807 ir,pro planet 642 bp ir.
extras : skywatcher f4 aplanatic cc, Baader MPCC MKIII Coma Corrector,Orion Field Flattener,zwo 1.25''adc.starlight maxi 2" 9x filter wheel,tele vue 2x barlow .

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Re: "ZigZag" Hot Pixels

#7

Post by Juno16 »


I didn't know that hot pixels had a repeating pattern, but it is a good idea for sure!

I don't use DSS anymore, but it looks like the hot pixel rejection settings are in "settings, stacking parameters, Cosmetic tab".

Capture.JPG
Jim

Scopes: Explore Scientific ED102 APO, Sharpstar 61 EDPH II APO, Samyang 135 F2 (still on the Nikon).
Mount: Skywatcher HEQ5 Pro with Rowan Belt Mod
Stuff: ASI EAF Focus Motor (x2), Orion 50mm Guide Scope, ZWO 30 mm Guide Scope, ASI 220mm min, ASI 120mm mini, Stellarview 0.8 FR/FF, Sharpstar 0.8 FR/FF, Mele Overloock 3C.
Camera/Filters/Software: ASI 533 mc pro, ASI 120mm mini, Orion SSAG, IDAS LPS D-1, Optolong L-Enhance, ZWO UV/IR Cut, N.I.N.A., Green Swamp Server, PHD2, Adobe Photoshop CC, Pixinsight.
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My Astrobin: https://www.astrobin.com/users/Juno16/
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Re: "ZigZag" Hot Pixels

#8

Post by brenski »


@yobbo89 and @Juno16 thanks both - that's really helpful
will give that a go later
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Re: "ZigZag" Hot Pixels

#9

Post by DEnc »


I'd guess the zig zag is due to residual periodic error in the mount.
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Re: "ZigZag" Hot Pixels

#10

Post by brenski »


DEnc wrote: Wed Feb 08, 2023 4:17 pm I'd guess the zig zag is due to residual periodic error in the mount.
...and possibly combined with my poor Alignment?
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Re: "ZigZag" Hot Pixels

#11

Post by Petrol »


I'm no expert but these things can often be a combination of issues. As already said, it looks an odd ditherIng dithering pattern assuming you have dithering enabled in the mount. I dither every 5 frames and it cancels out hot pixels. It also looks like there's errors in the mount. I very much doubt poor alignment but more of a problem with the mechanics or a cable fouling problem. HTH.

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Re: "ZigZag" Hot Pixels

#12

Post by DEnc »


As mentioned above, the artifact you posted probably can be remedied with dithering followed by pixel rejection.

But I think the pattern arrises from the mount’s periodic error. Assuming you hadn’t dithered the images, I tried approximating a plot of one of the pixel trails and fit a 2-period fourier function to it—it looks to be in the general ball park. The fit would be improved with corrections for mis-alighnment. The software PEMPro does all this, and creates a file that can be imported into compatible mounts to automatically correct for this error during tracking. Unfortunately, your mount isn’t among them.

Nonetheless it looks like you’ll be in good shape once you dither and reject!
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Re: "ZigZag" Hot Pixels

#13

Post by Juno16 »


Excellent DEnc!

I was really curious what could cause this pattern!
Yes PE.
Certainly dithering with help (or correct) the issue.
Might as well use cosmetic correction and a good pixel correction algorithm too.
Jim

Scopes: Explore Scientific ED102 APO, Sharpstar 61 EDPH II APO, Samyang 135 F2 (still on the Nikon).
Mount: Skywatcher HEQ5 Pro with Rowan Belt Mod
Stuff: ASI EAF Focus Motor (x2), Orion 50mm Guide Scope, ZWO 30 mm Guide Scope, ASI 220mm min, ASI 120mm mini, Stellarview 0.8 FR/FF, Sharpstar 0.8 FR/FF, Mele Overloock 3C.
Camera/Filters/Software: ASI 533 mc pro, ASI 120mm mini, Orion SSAG, IDAS LPS D-1, Optolong L-Enhance, ZWO UV/IR Cut, N.I.N.A., Green Swamp Server, PHD2, Adobe Photoshop CC, Pixinsight.
Dog and best bud: Jack
Sky: Bortle 6-7
My Astrobin: https://www.astrobin.com/users/Juno16/
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Re: "ZigZag" Hot Pixels

#14

Post by JayTee »


Do these artifacts appear on any of the individual light frames?
∞ Primary Scopes: #1: Celestron CPC1100 #2: 8" f/7.5 Dob #3: CR150HD f/8 6" frac
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Re: "ZigZag" Hot Pixels

#15

Post by brenski »


not that i can see. I think they're individual Hot Pixels rotating on the tracker
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