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M27 Dumbbell in HOO - Comments welcome

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#1 cyber

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Posted 17 July 2017 - 08:33 AM

After practicing a couple weeks with the ASI1600MM-C, I chose the planetary nebula M27 for my most ambitious project so far.

 

The outer wings of M27 are very faint and difficult to observe, especially from light-polluted areas like my home (SQM ~17.5)

That’s where narrow band filters really prove their worth: I was very pleased to see the outer halo after only 2 hours of exposure per channel while using very short, high-gain subs. (perfect for my cheap mount).

 

My Ha subs from the second night introduced some star bloat in the stack though and this initially resulted in bright red halos around the HOO stars.

So I decided to remove the stars from both channels, and only used the OIII stars after tonemapping the nebulosity.

 

get.jpg

 

I like the amount of detail that’s visible at full resolution. It completely blows away my previous DSLR image.

However, M27 contains beautiful knots around the central star, and I've found it very difficult to bring these out without making the picture look cartoonish or overprocessed.

 

The core is stupidly bright in both OIII and Ha.

I'm currently using HDRWaveletTransform on the stretched starless images, with a mask around the core and different settings for both channels, before combining them with PixelMath.

 

Is anyone here that processed this nebula before, willing to share some tips for controlling the core?

 

Anyway, thanks for looking.


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#2 jhayes_tucson

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Posted 17 July 2017 - 09:07 AM

Search my posts for M27.  I gave some processing tips in that thread.  (I'd look it up for you but I'm on my iPad and I don't have time right now.)

 

John


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#3 deSitter

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Posted 17 July 2017 - 09:29 AM

That is simply incredible. Well done!!

 

-drl



#4 jwheel

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Posted 17 July 2017 - 10:07 AM

waytogo.gif



#5 cyber

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Posted 17 July 2017 - 10:42 AM

Search my posts for M27.  I gave some processing tips in that thread.  (I'd look it up for you but I'm on my iPad and I don't have time right now.)

 

John

I found your post, thanks! 



#6 FiremanDan

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Posted 17 July 2017 - 10:58 AM

Very nice! Was this at your native FL or reduced? 



#7 cyber

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Posted 17 July 2017 - 02:43 PM

Thanks deSitter, jwheel and Dan.

 

This was captured with the TS 0.79X reducer, so M27 appears pretty small on the camera sensor.

The effective focal length should be ~379 mm with an image scale of 2.07 arc seconds per pixel. My guiding error varied between 0.9 and 1.2 arc sec RMS.

I cropped the 2X drizzled image to 4000x4000, applied DBE and deconvolution, then Resampled back to 50% for further processing.

 

OIII Full frame and crop.jpg

 

Here's a star analysis of the drizzled OIII master

 

OIII FWHM and eccentricity.jpg

 

The stars in the center are good, but get pretty ugly near the edge.

 

OIII Full frame stars.jpg

 

After the crop however, they look more acceptable.

 

OIII crop stars.jpg


Edited by cyber, 17 July 2017 - 02:45 PM.

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#8 cyber

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Posted 07 August 2017 - 03:24 AM

Update after 3 weeks of clouds: I finally shot some RGB data to color the stars, 30 minutes per filter.

get.jpg

The stars in the blue channel are a bit bloated, I'm a bit disappointed with the performance of my telescope. I focused through the green filter.

The RGB data was mildly stretched and added to the starless HOO image with PixelMath (Max function).

get.jpg
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#9 mdine1us

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Posted 07 August 2017 - 07:18 PM

Really nice result!


Edited by mdine1us, 07 August 2017 - 07:18 PM.


#10 cyber

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Posted 08 August 2017 - 11:20 AM

Thanks!

 

I like the RGB too, much better than my result from last year.

Here's a comparison of 30 minute exposures, shot from the same location (click for full resolution):

 

M27 2016 vs 2017 RGB.jpg

 

Left:

2016/08/23

Canon 450D

ST-80 telescope

61 x 30 sec

 

Right:

2017/08/06

ASI1600MM-C

TS 80mm APO telescope 

53 x 30 sec R

52 x 30 sec G

51 x 30 sec B

 


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