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What's wrong with this picture? Back spacing? Tilt? ?

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#1 marter

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Posted 03 December 2022 - 07:42 PM

I'm trying to set up a new scope (AT115EDT w/ Stellarvue FF) and think I have the back spacing correct, but maybe not. What's causing the stars in this image to elongate towards the upper right? Doesn't seem like the charts I've seen for back spacing issues. Is this tilt?

 

Also, what's causing the spikes on the larger stars?

Attached Thumbnails

  • 2022-12-03_02-01-45_L_-11.00_120.00s_101_20_1x1_0015.jpg


#2 Jim Waters

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Posted 03 December 2022 - 07:56 PM

I just looked at it with PixInsight and see very minor to no issues.  Some of the stars in the upper right are doubles or multiple stars in the same line of sight.  As for the small spikes, its likely due to the AT lens.  They aren't top quality but just OK.

 

Post a link to the raw image and I will look again.


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#3 marter

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Posted 03 December 2022 - 07:59 PM

I just looked at it with PixInsight and see very minor to no issues.  Some of the stars in the upper right are doubles or multiple stars in the same line of sight.  As for the small spikes, its likely due to the AT lens.  They aren't top quality but just OK.

 

Post a link to the raw image and I will look again.

Thanks. Give me a minute and I'll post a link.



#4 marter

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Posted 03 December 2022 - 08:06 PM

Here's a link to a single Lum sub and the stacked Lum master light. https://1drv.ms/u/s!...Ui-qNw?e=vdPHek

 

You're not seeing elongation in a lot of stars pointing to the upper right?

 

Thanks for taking a look.



#5 Jim Waters

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Posted 03 December 2022 - 08:21 PM

Looking at the image now with PI AberrationSpotter at 3x3.  There's some minor tilt towards that direction.  I am not at my laptop with ASTAP.  The analysis tool could give me an indication of how much.

 

Do you have ASTAP installed?



#6 marter

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Posted 03 December 2022 - 08:27 PM

Looking at the image now with PI AberrationSpotter at 3x3.  There's some minor tilt towards that direction.  I am not at my laptop with ASTAP.  The analysis tool could give me an indication of how much.

 

Do you have ASTAP installed?

Yes, I do, and I've looked at these with the Image Inspection tool. As far as the master light, ASTAP says the Tilt [HFD] = 0.45 (10% almost none) but I'm seeing enough elongation that I've convinced myself something is wrong. Just not sure what's causing it. I'd like to find out before my return window closes if I can.

 

Edit: I should mention these images were taken last night in a 20-30mph wind, although I think it died down before most of these images were taken. Not a great night for first light on a scope, but I wanted to dial in focus and see if I had any issues. Cloudy tonight and foreseeable future which is making evaluation difficult. However, that elongation doesn't look like the wind caused it.


Edited by marter, 03 December 2022 - 08:30 PM.


#7 Jim Waters

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Posted 03 December 2022 - 08:37 PM

Take some more images under better conditions and with good guiding.  Use a different star field too.

 

EDIT - Its Hit-or-Miss with mass produced scopes from China.  For this amount of tilt just adjust your camera's tilt plate.  MHO here.


Edited by Jim Waters, 03 December 2022 - 09:01 PM.


#8 marter

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Posted 03 December 2022 - 09:05 PM

Take some more images under better conditions and with good guiding.  Use a different star field too.

 

EDIT - Its Hit-or-Miss with mass produced scopes from China.  For this amount of tilt just adjust your camera's tilt plate.  MHO here.

I plan on that, but as I said the window for return is nearing and I'm not sure if I'll get any clear skies. The hit or miss nature is exactly what I'm concerned about. OTOH maybe I've convinced myself I have a problem when I don't.

 

Thanks again for looking.



#9 Tim0116

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Posted 04 December 2022 - 02:33 PM

I'm trying to set up a new scope (AT115EDT w/ Stellarvue FF) and think I have the back spacing correct, but maybe not. What's causing the stars in this image to elongate towards the upper right? Doesn't seem like the charts I've seen for back spacing issues. Is this tilt?

 

Also, what's causing the spikes on the larger stars?

My only scope is an AT115EDT, and the most interesting thing about this to me is the little spikes (seen on your fits file). I just went through a review of many frames taken through an L filter and don't see anything like that on stars of similar brightness. Your Chroma filters are vastly superior to my Antlia. Unfortunately, as a beginner myself, I have no answers!  That is an awful lot of wind, though. I've had "weird" results from wind that was no more than 10mph-ish on my EQ6R Pro. 

 

Also, I haven't been on here in a while and just found your comment on my Iris Nebula image from Oct... oops. Was not intentionally ignoring you! haha. Will message you soon about my rough processing take on that. 

 

Best with the troubleshooting. Backspacing is not a trivial thing when starting out. It's a fussy process. Tilt... even worse!


Edited by Tim0116, 04 December 2022 - 02:33 PM.

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#10 marter

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Posted 06 December 2022 - 09:44 AM

Take some more images under better conditions and with good guiding.  Use a different star field too.

 

EDIT - Its Hit-or-Miss with mass produced scopes from China.  For this amount of tilt just adjust your camera's tilt plate.  MHO here.

It's amazing what the lack of 20-30 mph winds makes on a 115 scope. Got 3+ hours on the Monkey Head Nebula a couple nights ago and hope to add more tonight. Guiding was running in the 0.3 to 0.4" range with PHD2 logs showing an average of just below 0.6". Seeing was okay and FWHMs were in the high 2s/low 3s. I feel like my back spacing is correct, but still see a bit of elongation in the upper right corner, not so much across the rest of the image. Is that likely due to tilt? I get a range of readings from NINA's Hocus Focus Aberration Inspector. But overall I feel a lot better about the scope and my mount's ability to handle it. At least when the winds aren't blowing.

 

Below is an image NGC 2174 Monkey Head Nebula, processed in PI from 12-15 subs each of Ha, Sii and Oiii, total time at 3h 25min. Obviously need more integration time but would appreciate any comments on the image as it relates to the AT115EDT or any tilt, etc.

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  • NGC2174_Monkey_Head_Nebula_low.jpg


#11 Jim Waters

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Posted 06 December 2022 - 04:06 PM

"But overall I feel a lot better about the scope and my mount's ability to handle it."  Good

 

Nice image marter.  Some questions and comments.

  • Did you do Drizzle Integration?  If not give it a try.  Sometimes it has a tendency to blur nebulas so you need to play around.
  • The Monkey Head nebula has fine structure and a large dynamic range.   Do you use Deconvolution, UnsharpMask or HDRMultiscaleTransform?
  • My high level processing steps for images like this are...
    • WBPP
    • DynamicBackgroundExtraction 
    • ColorCalibration
    • NoiseXTerminator
    • HistogramTransformation
    • StarXTerminator to split the image into two
      • Star Image
      • SCNR
      • CorrectMagentaStars
      • Invert
      • SCNR
      • CurvesTransformation
      • Nebula Image
      • There's no set process flow.  I use a mix of Deconvolution, UnsharpMask or HDRMultiscaleTransform and the standard ColorSaturation, CurvesTransformation, AdvSharpening ...etc.
    • PixelMath (Stars + Nebula)
    • BillsStarReductionMethods_V3 and usually kill the stars by 50%
    • etc.

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#12 marter

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Posted 06 December 2022 - 04:41 PM

Thanks Jim.

 

I've tested drizzling and found it only worked for me if I was undersampled, so I've been using it with my FRA400 and 0.7x reducer only. With that, I use 2x drizzle with a .85 drop shrink. Creates a pretty big output directory and project folder. Are you finding it valuable when you're not undersampled?

 

The image I posted was only 3+ hours so I didn't spend an inordinate amount of time on it. I did run EZ Decon on it, then BIll's color filters to adjust curves, then EZ Denoise and that's about it. I usually use Bill's StarReductionMeth3 with a setting of 2 and 2 but since I was concerned about star elongation and focus I didn't want to reduce the stars in the "test" image. Blanshan's done some great work for the community, I really like his normalization scripts for SHO and HOO.

 

I'm hoping to get another 4 3/4 hours on it tonight and I'll spend more time post processing that image.



#13 Jim Waters

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Posted 06 December 2022 - 06:01 PM

If I am not under sampled its hit-or-miss when I try using it.  Good luck with imaging tonight.  Repost the final image.


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#14 marter

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Posted 07 December 2022 - 11:20 PM

If I am not under sampled its hit-or-miss when I try using it.  Good luck with imaging tonight.  Repost the final image.

Got another 3+ hours last night, so here's another take on the Monkey Head. Jumping from a 400mm scope to an 800mm is a learning curve, still on it. Glad I bought the scope.

Attached Thumbnails

  • NGC2174_low.jpg

Edited by marter, 07 December 2022 - 11:21 PM.



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