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Hunting Absorption Nebulae

EAA NV
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#1 GeezerGazer

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Posted 13 August 2019 - 09:18 PM

About 10 days ago, I was in Nevada at the Berlin-Ichthyosaur State Park, which is in a very dark part of Nevada about 150 miles S/E of Mono Lake.  The closest habitation of about 60 people is the mining community Gabbs, 20 miles distant and on the other side of mountains that completely block any light from this isolated “town” which has no active store or gas station.  People who live there may have to drive to Hawthorne, NV, which is 1.5 hrs. away on fast roads just to get an egg.  For the last hour getting to the Park, I did not pass a single vehicle in either direction.  When the paved road comes to an end, you know you are only 5 miles from the park, on a dusty but graded unpaved dirt/gravel road. 

 

I don’t have an SQM, but this site is dark. I’d guess SQM 21+.  It’s charcoal color on the world light pollution map.  At night, no light sources are visible except for what you bring and I could see no light domes in any direction. 

 

I was there two nights by myself and 3 nights with OFLI (the Off Fisher Lane Irregulars) observing friends Jeff C. and Jim B. also from N. California.  This was not our first trip to observe here.  Naturally, I brought my NVD. 

The first night, I only used my 50, 105 & 300mm camera lenses with night vision and either my FujiFilm Camera XT30, or my iPhone XR  for imaging a variety of large nebula.  The second night, I used my ES 208mm Newt, either with an MPCC at f:4 or with an ASA .73x reducer at f:2.8. 

 

DISCLAIMER: Taking images is different than the visual use of NV.  It is more akin to EAA because with my phone, I use up to 1 second exposures and automatic electronic photo averaging for results.  With my Fujifilm XT30 camera, I take up to 20 second single exposures.  If you have no interest in these results, please just skip this thread.  Photo results differ from using NV visually.  

 

Edggie had posted a photo and description of the Ink Spot dark nebula a couple of weeks before this trip and his post had peaked my curiosity about dark nebulae, also known as absorption nebulae, mainly found within the Barnard Catalogue.  So before the trip, I made a list of possible candidates, using both the Bracken Astrophotography Sky Atlas and the S&T Pocket Sky Atlas… both include partial indexes of Barnard objects.  Then I found “The Best of Barnard’s Dark Nebula,” a list composed by the Saquaro Astronomy Club that I found very helpful as it gives simple/brief directions to the Barnard subject from numbered NGC or Messier objects:

Unfortunately, I was star hopping to these objects because my GoTo mount does not include a catalogue of Barnard objects.  It takes longer to find them! 

 

I found that these nebulae are pretty difficult for me to see visually, even with NV, especially if the surrounding sky area is black; visually, I was looking for the absence of stars.  But if they are associated with an emission nebula, use of an H-a filter helped substantially to see them materialize.  I used only a 12nm filter where necessary for photos (e.g., within IC 1396).  A very dark sky is also a big asset for better contrast.  There is an abundance of dark nebulae found near the Milky Way central bulge, but they are not limited to that area of the sky. 

 

I was surprised to find Barnard 85 located inside of M20, the Triffid.  M20 is unique in that it includes emission, reflection and dark nebula.  What I thought was part of the cloud-like emission nebula in M20, is actually an absorption nebulae that shows up prominently in almost every photo I’ve taken of M20.  In the photos below, B85 is either circled or has an arrow to point it out.

 

ES 208 + 2x Barlow + 7nm H-a.  iPhone XR, ISO 4000, 1/4s exp. averaged 10s.

IMG_5207.jpg
 

ES 208 + 12nm H-a.  iPhone XR, ISO 5000, 1/2s exp. averaged 15s.

IMG_2334.jpg

Likewise, B88, B89, and B296, all three being small, dark nebulae, take up residence in M8, The Lagoon Nebula.  I have seen and photographed M8 many times without realizing that these small dark patches are catalogued… a demonstration of my ignorance about things I may take for granted! They are identified individually in this photo:

 

ES 208 + MPCC + 12nm H-a.  iPhone XR, ISO 1600, 1/2s exp. averaged 10s.

IMG_5208.jpg

 

IC1396, the very large, but faint emission nebula in Cepheus, has numerous dark lanes but only one is catalogued… Barnard 163.  I did not photograph it because I did not know exactly where it was located within IC 1396.  But now I do and next time out, I’ll try to photograph it.  In this photo of IC 1396, I thought the dark spot at about 7 o’clock might have been it, but B163, is about one full FoV farther south.   You can see in this internet long exposure image where B163 is located (faintly outlined in a green box):

https://epod.usra.ed...396-nebula.html

The dark spot in my image is about the same size at B163, but B163 looks more like a bee in flight. 
 

ES 208 + MPCC + 12nm H-a.  iPhone XR, ISO 6400, 1/3s exposure/averaged 10s.

IMG_5096.jpeg

 

The Snake Nebula, B72, in Ophiuchus was an easy find.  I photographed it with both my phone and a Fujifilm XT30 for a little comparison.  These images were taken at the same FL but the Fuji attaches closer to the NV ocular, so the image fills more of the camera sensor.  Using the phone which uses a slightly wide angle lens, the lens/sensor is farther from the ocular, so it takes a photo of the circular image emitted by the NVD.  I’ll Probably add a spacer to the Fuji camera connection as I like seeing the full round ocular image.

 

ES 208 + MPCC.  Fujifilm XT30/35mm lens, ISO 100, 5s exp. (This camera provides a lot more detail than my phone images)

XT300236.jpeg

 

FOR COMPARISON:  this photo was taken using the iPhone XR, ISO 250, 1/4s averaged 8s.

IMG_5130.jpg

 


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#2 GeezerGazer

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Posted 13 August 2019 - 09:27 PM

Next, are two images of the Pipe, comprised of Barnard 59,65,66,67 and 78 located adjacent to the Snake in Ophiuchus.  This one is naked eye visible in the southern US from clear and dark skies, but is better in binoculars… it’s big!  These two images show the straight line of the Pipe stem (partially in both photos) and the bowl of the pipe, “with smoke.”  The really obvious thing about this photo is how background stars are totally or partially blocked.

 

ES 208 + MPCC.  iPhone XR, ISO 200, 1/2s Exp. averaged 8s (for both images)

IMG_5120.jpeg

 

IMG_5121.jpeg

 

Moving north from the Snake Nebula, I ran into some dark lanes which might be B-62, but I could not confirm.  I photographed them but could not identify them when compared to other images.  

 

This was an interesting hunt and I want to thank Edggie for his report which inspired me to take a look at dark nebulae.  I feel like they provide one more facet of the night sky that I had ignored far too long.  I looked at and photographed many more, some of which I could not positively identify.  I think next time I’ll log Lat/Long so I might be sure of their identity... as I store them in a new photo album on my computer. 

Clear Skies.
Ray

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#3 GeezerGazer

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Posted 13 August 2019 - 09:42 PM

I should have mentioned that the two images of the Snake Nebula include a second Barnard subject. The Snake is B72.  The small patch of black below the Snake head is B68... should name it the "mouse" since the snake looks ready to strike! 

 

Also, all images are straight from the camera; no post processing except to crop and compress to fit here.  For instance, the Fujifilm photo of the Snake Nebula was 7mb, compressed to 62kb!


Edited by GeezerGazer, 13 August 2019 - 09:47 PM.


#4 Eddgie

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Posted 13 August 2019 - 09:49 PM

A most excellent report, and thank you for the shout out.  

 

Yes, H-a gets all of the attention, but dark nebula is profuse along the Milky Way.  Some of these are dust lanes, and some are absorption nebula.  This summer, I have been doing more dark nebula work than anything else and this is almost all very low power work, so I use 1x, 3x, 7x, and 17x for most of this.

 

The problem, as you have seen, is that it can be difficult to make positive identification.  I have seen one chart that showed over 100 nebula locations, but it only showed boxes (I forget the link) and not pictures of the objects. 

 

 

I am very happy that my post spurred you to look harder at these under-appreciated DSOs. Even if we have trouble identifying them, the search is a lot of fun!



#5 GeezerGazer

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Posted 13 August 2019 - 11:23 PM

Thanks again Ed.  

 

The Saguaro Best of Barnard list does include coordinates, so next outing I'll be checking them on my AZ Pro mount.  

 

Reading about some of these objects is as fascinating as seeing them.  

 

I did find this 5 hr. long exposure on-line which indicates that there are several Barnard objects within IC 1396 (not just B163):  http://cs.astronomy....lae/490902.aspx



#6 cnoct

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Posted 14 August 2019 - 02:23 AM

There's a lot of effort hidden in this post, very deep yet concise. I very much appreciate the photos and time it took to include them.

 

The X-T30 photo has a lot of dynamic range, hope to see more with that camera.

 

What 35mm are you using, Fujifilm x-series, f/1.4r, f/2 ?


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#7 GeezerGazer

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Posted 14 August 2019 - 11:16 PM

Thanks cnoct.  Yes, the lens was the XF 35 f/2.  This was my first outing with the X-T30, but I'll be doing more with it in the future.  I do like the manual controls on the Fujifilm... they are sort of old-school and very convenient.  



#8 Jeff Morgan

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Posted 16 August 2019 - 01:23 AM

The problem, as you have seen, is that it can be difficult to make positive identification.  I have seen one chart that showed over 100 nebula locations, but it only showed boxes (I forget the link) and not pictures of the objects. 

 

Uranometria 2000 is excellent for dark nebula identification. The are drawn as outlines, not symbols or boxes.



#9 Jeff Morgan

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Posted 16 August 2019 - 01:34 AM

Then I found “The Best of Barnard’s Dark Nebula,” a list composed by the Saquaro Astronomy Club that I found very helpful as it gives simple/brief directions to the Barnard subject from numbered NGC or Messier objects:

Unfortunately, I was star hopping to these objects because my GoTo mount does not include a catalogue of Barnard objects.  It takes longer to find them! 

 

That is a nice list!

 

Here is an old thread that may suggest a few candidates for you:

 

https://www.cloudyni...ulae/?p=2789474


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#10 cnoct

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Posted 16 August 2019 - 07:02 AM

Have always been curious about the X-Trans filter array, specifically if the X-Trans array would be a better match for P43 phosphor than the conventional Bayer array.

 

Thought the X-Trans had something like 10% more photosites dedicated to green than Bayer arrays.

 

Don't remember if you use P43 tubes, if you do, I'd be interesting in hearing how the sensor performs with it as compared with P45.



#11 bobhen

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Posted 16 August 2019 - 02:18 PM

Even with NV, I was still shocked to see these dark nebulas so easily from the Philadelphia suburbs.

 

Come to think of it, I haven’t observed too many objects that were not enhanced with NV.

 

Good stuff.

 

Bob


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#12 GeezerGazer

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Posted 16 August 2019 - 08:06 PM

Have always been curious about the X-Trans filter array, specifically if the X-Trans array would be a better match for P43 phosphor than the conventional Bayer array.

 

Thought the X-Trans had something like 10% more photosites dedicated to green than Bayer arrays.

 

Don't remember if you use P43 tubes, if you do, I'd be interesting in hearing how the sensor performs with it as compared with P45.

I use a P-45 tube; sometimes green image, sometimes blue, depending on where I set the white balance.  The X-Trans sensor does have a different array, but I have no idea whether it would provide any meaningful difference for green phosphor NV images.  Interesting question though.  I went to the X-T30 mainly for its size (small), for its convenience in accessing manual controls, and for the articulating screen for straight-through photography with my Nikon lenses.  

 

For those scratching their heads, look at this article about Bayer vs. X-Trans sensors:

https://petapixel.co...ic-claims-test/



#13 GeezerGazer

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Posted 16 August 2019 - 08:07 PM

Here is an old thread that may suggest a few candidates for you:

 

https://www.cloudyni...ulae/?p=2789474

Good resource for favorites!  Thanks.



#14 GeezerGazer

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Posted 08 September 2019 - 02:53 AM

Recently I had two nights of very steady, transparent skies; I observed from midnight until dawn both nights as that was when things really settled down.  So I returned to IC 1396 to see what I could find and identify.  I used my 8" Newt first and took some photos of individual areas within IC 1396.  Then I used a Nikon 300mm f:2.8 lens with the Mod 3C which has about a 4° FoV.  IC 1396 is all of 3° in diameter, so this objective lens with NV was quite good for scale to see where parts were located with enough magnification to identify them.  For comparison, I'll include one of 6 photos taken with the 8" Newt (1° FoV) and another taken using a Nikon 105mm (10° FoV), neither of which seemed right for this subject. 

 

This image was using the Nikon 300, 7nm H-a filter, iPone XR, with NightCap Camera app set ISO 6400, 1/4s exposure, averaged 15s.  

 

IMG_5416.jpeg

 

 

 

 


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#15 GeezerGazer

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Posted 08 September 2019 - 02:55 AM

This image was taken using the 8" Newt and 7nm H-a filter, ISO 5000, 1/4s exposure, averaged 15s

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#16 GeezerGazer

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Posted 08 September 2019 - 02:57 AM

And this image of IC 1396 was taken using a Nikon 105 with 7nm H-a filter, ISO 5000, 1/10s exposure, averaged 10s; the scale is just too small.  If you click on these images, they will enlarge with pretty good detail. 

 

IMG_5465.jpeg


Edited by GeezerGazer, 08 September 2019 - 03:06 AM.


#17 Jeff Morgan

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Posted 08 September 2019 - 04:50 PM

Great images!

 

Since you are after absorption nebula, I am wondering how you would do unfiltered?

 

With conventional eyepieces, I often use the "edges" of star fields to trace and ID dark nebula. H-alpha is great for the emission nebula that highlights some dark nebula, but for others cuts down the background stars substantially.



#18 GeezerGazer

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Posted 08 September 2019 - 09:14 PM

Jeff, I've found, at least for imaging, that if the dark nebula is embedded in H-a, then filtration helps a lot because it brightens the H-a background surrounding the dark nebula, increasing contrast.  If the dark nebula is in a nice dark part of the sky, like the Ink Spot, then unfiltered is much better visually and for images.  This image of the Ink Spot, Barnard 86 with open cluster NGC 6520, is an example, taken with ES 208 w/ASA reducer at f:2.8, ISO 320, 1/7s exposure, averaged 15s... and no filter.  If you go back to the marked up image of IC 1396, you'll see how the filtration effects the image when H-a is the background, especially for faint dark nebulae like B-367, the darker smudge or blot near the center of the image.  

 

IMG_E5026.jpeg


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