Quick Dithering Question

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Baskevo
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Quick Dithering Question

#1

Post by Baskevo »


Hi guys,

For some reason, when I dither in both axes, my DEC can't handle it and takes forever to respond. Does it hurt my images if I only dither in RA? Or does anyone know how I can fix this issue? Is it from backlash?
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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yobbo89 Australia
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Re: Quick Dithering Question

#2

Post by yobbo89 »


The only thing I can see that may be a problem dithering in Ra only is "walking noise" I guess it depends what camera you have.what is your guide calibration like for the Dec? Dose it take awhile for it to calibrate?.
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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bobharmony
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Re: Quick Dithering Question

#3

Post by bobharmony »


James, yes it is sounds like DEC backlash. I tried doing RA-only dithering one time, the walking noise was pretty apparent so I gave up on the experiment.

My rig has a lot of DEC backlash, but there doesn't seem to be much of a downside in it, DEC normally performs better than RA for me when I look at RMS ranges.

Bob
Hardware: Celestron C6-N w/ Advanced GTmount, Baader MK iii CC, Orion ST-80, Canon 60D (unmodded), Nikon D5300 (modded), Orion SSAG
Software: BYE, APT, PHD2, DSS, PhotoShop CC 2020, StarTools, Cartes du Ciel, AstroTortilla

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Re: Quick Dithering Question

#4

Post by Baskevo »


yobbo89 wrote: Fri Apr 24, 2020 6:07 am The only thing I can see that may be a problem dithering in Ra only is "walking noise" I guess it depends what camera you have.what is your guide calibration like for the Dec? Dose it take awhile for it to calibrate?.
I have an ASI1600mm Pro, and what I usually do is dither in both axes until the DEC stops correcting, where it takes like 90 seconds for it to recover (it ranges, but that's probably average), and then when it does that a few times I switch to RA only. But now it is getting so bad that I usually start RA only toward the beginning of my sessions :(

Calibration doesn't seem like it takes longer than it is supposed to, I am not totally sure though... I haven't redone my calibration in a while because my guiding has been so good as of late, and the last time I tried to re-calibrate, I got a bunch of these errors like couldn't make sufficient corrections and that I should guide in only one direction... So I restored the old calibration and it has worked great. I don't even use the guiding assistant it has been so good.
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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JayTee United States of America
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Re: Quick Dithering Question

#5

Post by JayTee »


James,

Are you using "Backlash Compensation" in PHD2?

JT
∞ Primary Scopes: #1: Celestron CPC1100 #2: 8" f/7.5 Dob #3: CR150HD f/8 6" frac
∞ AP Scopes: #1: TPO 6" f/9 RC #2: ES 102 f/7 APO #3: ES 80mm f/6 APO
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∞ Guide Scopes: 70 & 80mm fracs -- The El Cheapo Bros.
∞ Mounts: iOptron CEM70AG, SW EQ6, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
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Juno16 United States of America
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Re: Quick Dithering Question

#6

Post by Juno16 »


I’ve also experienced walking noise with dithering in RA only. I also have HUGE DEC backlash. To me it is worth the wait to set the settling time long enough for things to get back under control. I’m using a dithering setting of 3 in APT with no multiplier in PHD2 and my dithers usually settle in 30-40 seconds. Every now and then longer, but like Bob said, my DEC guiding is always better than RA.
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: Quick Dithering Question

#7

Post by Baskevo »


JayTee wrote: Fri Apr 24, 2020 10:38 pm James,

Are you using "Backlash Compensation" in PHD2?

JT
No I do not. When I have tried that, I felt like my guiding got worse--sometimes much worse--but that was probably my fault somehow...
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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Re: Quick Dithering Question

#8

Post by Baskevo »


Juno16 wrote: Fri Apr 24, 2020 10:42 pm I’ve also experienced walking noise with dithering in RA only. I also have HUGE DEC backlash. To me it is worth the wait to set the settling time long enough for things to get back under control. I’m using a dithering setting of 3 in APT with no multiplier in PHD2 and my dithers usually settle in 30-40 seconds. Every now and then longer, but like Bob said, my DEC guiding is always better than RA.
Really? Imaging time is precious to me I couldn't imagine... Especially lately since it has been so cloudy. I'm using a dithering setting of 2 in APT, I do not think I am using a multiplier in PHD2, but I will double check. Sometimes it works totally fine, but at some point in the night it gets really bad, I'm assuming when it tries to dither a certain direction...
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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Re: Quick Dithering Question

#9

Post by bobharmony »


I set APT dithering distance to 2, PHD scale to 1. I have recently tried using the mounts DEC backlash setting using the hand controller to offset backlash. Early indications are that I am getting my best guiding ever, but I don't have enough experience with this yet to declare success.

Steve333 posted a calculation a few months back that compares imaging camera scale to guide camera scale. This was very useful to me in setting APT and PHD2 dithering parameters.

Bob
Hardware: Celestron C6-N w/ Advanced GTmount, Baader MK iii CC, Orion ST-80, Canon 60D (unmodded), Nikon D5300 (modded), Orion SSAG
Software: BYE, APT, PHD2, DSS, PhotoShop CC 2020, StarTools, Cartes du Ciel, AstroTortilla

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Re: Quick Dithering Question

#10

Post by Graeme1858 »


bobharmony wrote: Sat Apr 25, 2020 2:49 am Steve333 posted a calculation a few months back that compares imaging camera scale to guide camera scale. This was very useful to me in setting APT and PHD2 dithering parameters.

This one?

viewtopic.php?f=24&t=6851&p=58822&hilit=Graeme#p58685

Regards

Graeme
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Celestron 9.25 f10 SCT, f6.3FR, CGX mount.
ASI1600MM Pro, ASI294MC Pro, ASI224MC
ZWO EFW, ZWO OAG, ASI220MM Mini.
APM 11x70 ED APO Binoculars.

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Re: Quick Dithering Question

#11

Post by Baskevo »


Yeah I remember that... I think all that is good, if I calculated correctly I am dithering around 8 image pixels
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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Re: Quick Dithering Question

#12

Post by Baskevo »


So I just stacked the frames for my latest project, and the walking noise was pretty bad... I think the long settle time for dithering is fine for 1 and 2 minute subs, but when I get up to 5 minutes for narrowband, I notice that I'll have frames where the stars are trailing. Also, I'd rather not wait 2 minutes for my dithering to settle... So is there anything else I can do without opening up my mount?
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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