M27 Dumbbell imaged with an Alt/Az Goto Dobsonian

[Smiller]

Got a few hours on M27 and tried for a combination of decent details with a larger FOV.

So, I shot about 4 hours of data (3000 * 4 second exposures) with my ASI2600MC/Baader Coma corrector (F4.9) for details on the nebula with about 4 hours (1500 * 8 seconds) of exposures with my larger pixel ASI2400MC with my Nexus at F3.7  for a larger field of view (actually cropped to 70% of the frame, so the FOB wasn’t too large) and for more subtle nebulosity details.  

I have the full FOV along with a crop shown for your convenience.

 

 

Stats:
Telescope:  Stock Orion XT12G 12" Goto Alt/Az Dobsonian

Camera/Corrector combos:  ASI2600MC with Baader Mark III CC (0.52"/pixel) and ASI2400MC with Nexus 0.75xReducer (1.08"/pixel)

Capture:  ~3000*4 second exposures (ASi2600MC) + ~1500 * 8 second exposures (ASI2400MC)

Filter: Optolong L-Ultimate on both

Processing: Stacking in SIRIL, processing in APP/PI/Affinity with the Xterminators

Sky conditions:  Bortle 6/7, Good clarity, little wind, above average seeing, nearly full moon

 

Edited July 6, 2023 by Smiller

[Elp]

This is actually quite incredible and shows the value for consideration of total integration time over length of singular subs. The large scope is quite something.

Edited July 6, 2023 by Elp

[Chris-h]

Wow, it looks amazing!

[Smiller]

8 hours ago, Elp said:

This is actually quite incredible and shows the value for consideration of total integration time over length of singular subs. The large scope is quite something.

Yes, absolutely it’s total integration time.  Even with the Optolong L-Ultimate with its very narrow 3nm/3nm bandpass I’m still sky noise limited at 8 second exposures on the ASI2400MC at f3.7, although just barely with the smaller pixel ASI2600MC at f4.9.

 

The miracle of these low read noise cameras, fast optics, and high QE.

Edited July 6, 2023 by Smiller

[Elp]

You might find you can expose for longer if you can counter the field rotation. My hyperstar preview pretty much looks white in the middle of the image like a flat (with auto stretch on), histogram peak is usually in the middle so not clipped. All is revealed after calibration.

[Smiller]

My exposure time limit is primarily tracking accuracy and smoothness.  Much over 10 seconds and each sub gets a bit unreliable with respect to star quality.  The main issues are that a big Dob is very sensitive to the slightest air movement and the tracking motion isn’t silky smooth but tends to wander a few pixels here and there over a 20-30 second timeframe.   Field rotation doesn’t kick in until I’m shooting much over 60 degrees to the North or South.  Then it can limit me to 8, then 6, and finally 4 seconds.   For most targets this never happens.

I can reduce field rotation a bit by angling the base of the scope 5-8 degrees North or South depending on target location, but that’s a new concept that I’m testing to ensure it doesn’t degrade scope tracking.

Edited July 6, 2023 by Smiller

[windjammer]

A fantastic result- beautiful.  Re your tracking accuracy and smoothness issues, I have similar problems with my homemade GEM (gears are not high precision - made out of cordless drill gearboxes), and I live near a busy road and railway line so ground vibrations.  I got over the tracking by using PHD and guiding at 10 to 20msecond exposures with 100msec between exposures.  This boxes in the mount and drags it back on track before it wanders too far. For the vibration I made a mechanical shutter - a filter wheel that shuttles back and forth between an open hole and a black filter.  When the PHD control lines (I use ST4) waggle up and down too much the shutter closes and saves the exposure.  Similar approach might  work for you ?

Simon

[FaB-Bo-Peep]

Absolutely stunning!

[peter shah]

super work on that...beautiful outer shell

[Blauvista]

I am always amazed with the ingenuity by which people arrive at the results they do - very impressive result with lovely detail! 👍 With so many exposures are you using some "lucky imaging" sorting to find the better subs or are all of the subs ending up in the final stack ? ... Is 3000 enough for "lucky imaging" ? 

[Smiller]

On 08/08/2023 at 08:43, Blauvista said:

I am always amazed with the ingenuity by which people arrive at the results they do - very impressive result with lovely detail! 👍 With so many exposures are you using some "lucky imaging" sorting to find the better subs or are all of the subs ending up in the final stack ? ... Is 3000 enough for "lucky imaging" ? 

Sorry for the delayed response but I’ve been away for awhile.  Yes, with so many exposures you can do more aggressive sorting to increase the spatial, resolution but the opportunity is limited to brighter objects where yiu can afford to “toss some photons” for the sake of resolution.  It really works better for the brightest broadband targets like star clusters, binary stars, and the brightest galaxies and perhaps the cores of a few nebula.  M27 is a borderline target in this regard.

[tooth_dr]

Amazing detail in the core, nebulous looking.  Superb