[Theme] Night sky shots

[Øivind Tøien]

Thanks for the kind comment, Paco.

The end of last weekend was supposed to be cloudy but I had a clear enough period in the evening for another try the at Veil Nebula with my 300mm f/4 PF on the Skytracker. I deleted frames with satellites and 2 or 3 where things apparently slipped. I then asked DSS to stack 90% of the remaining raw files in intersection mode, and it had apparently no problems with including a few frames from last session above, although it lost me some area at the bottom of the frame. A total of 50 subs, each 1 minute were used with 5 of those subs coming from the last session. I also cropped somewhat at the top, so likely 70% of the recorded frame is included. I used the darks from both days (total about 50) as temperature did not differ much, and used biases only from last day + flats. Initial saturation and RGB level adjustment was performed in DSS and final RGB level adjustment and stretching in CNX2. I had to try compensate some apparent gradients this time.



Veil Nebula (NGC 6992) with Nikon D7100 and 300mm f/4 PF @ f/4.5 front aperture,  stack of 50 subs each 1  min, ca. 50 darks, + bias frames and flats, cropped  to ca. 70% of the initial frame.

While focus was right on at the start I was not 100% satisfied with the focus towards the end; a check with the Bahtinow mask indicated it was slightly off in spite of a refocus in the middle of the session (but I did not use the last hazy part after it cleared a tree top that got in the way). May be the image could benefit from some star shrinkage to better show the faint structures in the middle, however I have not learned how to do that yet.

This is recorded from a red zone with respect to light pollution, but with still no snow on the ground it gets a little darker.

[Øivind Tøien]

I got another dark night with no snow appearing yet. One of my targets was the Heart Nebula, but before it came into unobscured range at the setup in front of my cabin and the moon set, I had some time for another attempt at the Veil Nebula, this time being very picky with focusing, and providing somewhat better framing. The images below were stacked in Deep Sky Stacker, and further stretched and RGB level adjusted in CNX2 (best viewed large opened in a new tab).
#1

Veil Nebula with Nikon 300mm f/4 PF at f/4.5 front aperture, Stack  with 134 minutes integration time, one minute subs at ISO 1600, 140 darks, 25 bias and 35 flat frames.


Heart Nebula with "escaping" Soul Nebula at the top. Although I use a stock D7100, it is possible to pick up a considerable amount of red hydrogen emission. I just learnt that it appears red when partly obscured by dust, while the un-obscured emission has natural color that is leaning towards purple due to other spectral lines than hydrogen alpha (for instance blue hydrogen beta emission). This can be observed in some of the brighter areas.
#2

Heart Nebula (IC1805) and partial Soul Nebula with Nikon 300mm f/4 PF at f/4.5 front aperture,  Stack with 122 minutes integration time, one minute subs at ISO 1600, 140 darks, 25 bias and 35 flat frames.


When finished, the Pleiades was in a good position, so even if it was late, I wanted to use this unexpected clear night fully.
#3

Pleiades (M45) with Nikon 300mm f/4 PF at f/4.5 front aperture, Stack with 35 minutes integration time, 30sec. subs at ISO 1600, 160 darks, 25 bias and 35 flat frames.

[Birna Rørslett]

Apparently you have mastered the technique, Øivind ... I am partial to the last one in particular. Is the soft (and pretty) glare around the stars a result of the optics (300PF) only?

[Øivind Tøien]

Apparently you have mastered the technique, Øivind ... I am partial to the last one in particular. Is the soft (and pretty) glare around the stars a result of the optics (300PF) only?

Thanks for the kind comment, Birna.
The glare around the stars is mostly due to nebulosity. I reduced the exposure of each sub-frame to 30 seconds in order to minimize flare. There is a minimal amount of flare (not typical PF flare) that can be seen around the central portion, but otherwise we are seeing the effect of interstellar dust. One can see some patterns to it, particularly around the bottom star. These are very hot and young stars, formed only 100 million years ago according to the wiki.

A side note is that I think that the the nebulosity around the Pleiades explains why even a 10.5 mm fisheye with very tiny physical aperture can pick up this small constellation. Stars are single point light sources where the physical aperture opening not the f/stop number determines the light gathering, while nebulosity distributed over an area should obey regular photographic rules and be sensitive to the aperture value just like in regular photography.

[Øivind Tøien]

Here is a link to a fantastic image capture showing how dust is distributed around the Pleiades region and more:
https://astrob.in/full/368480/0/
I found the link here: https://www.cloudynights.com/topic/634578-from-pleiades-to-california-%E2%80%93-a-dusty-mosaic/

And another link with a more detailed view of the dust down the page - lots of fantastic images:
https://www.theguardian.com/science/gallery/2018/oct/24/astronomy-photographer-of-the-year-2018-the-winning-images

[Øivind Tøien]

A deep sky imaging session was suddenly interrupted by a full blast of aurora a few days ago.



(Recommend opening it in a new tab with dark background.)

[Bent Hjarbo]

Nice interruption.

[armando_m]

Wonderful alternative!

I was all set to go shoot the night sky, nature had other plans and the sky was covered in clouds

[timh]

Wow, a very impressive sight!

[Øivind Tøien]

Thanks for the comments, Bent, Armando and Tim. Sorry it did not work out for you Armando.

In spite of the aurora, I actually got in some time on the North America and Pelican Nebulas, this time using my D5100 with good framing before the abrupt onset of the green veil - up to that point it was nice and clean. However I discovered how weak the EN-EL14 battery is with respect to cold at -16°C. I lost a lot of time as I am used to 2-2.5 hours at even lower temperatures with the D7100 and did not foresee when to get out and change the battery. A test I performed with a warm, freshly charged battery when exposing the dark frames afterwards only lasted for 35 minutes with the D5100. It is not so much charge capacity as the voltage drop with lower temperature in combination with the threshold cutoff voltage of the body - after warm up the battery showed all the bars on the display.

I have been pondering whether to get a refurbished D5300 to save my neck and better noise performance during these sessions. However this night's experience with the weak D5100 battery performance might make me lean towards a D7500 or D500 although the D5300 is known for lower dark current while read noise is lower in D7500 : https://stargazerslounge.com/blogs/entry/2004-d7500-has-high-thermal-pattern-noise/

Anyway here are the two nebulas with the 300mm f/4 PF (with f/4.5 front aperture) on D5100, stack of 36 one minute frames at ISO 1600 on the SkyTracker. As usual best viewed when opened in new tab:
#1


It looks like there was some haze judged by the brightest stars.

An attempt on the North America and Pelican Nebulas a few nights before did not have as nice framing but better atmospheric transparency together with twice as much integration time, 77 one minute frames total of which 95% were stacked = 73 minute total integration time at ISO 1600, 96 darks and 20 bias frames. This deep sky target is quite beautiful and quite easy to frame once familiar with it, so I will keep trying for even better results once I get the chance.
#2



The same night when the above target went out of range I made an attempt on the Triangulum Galaxy. I got in 90 one minute frames of which 95% were stacked = ca. 85 minutes total integration time at ISO 1600.
#3



Finally a few nights before, also a first for me, I imaged the Elephant's Trunk Nebula, a hydrogen emission nebula, stack of 76 one minute frames.
#4

[Øivind Tøien]

Last night I was able to collect more data on the North America and  Pelican nebulas again in spite of weak moonlight and more light pollution.  I used Microsoft Image Composite editor for the stitching with the last image of the North America and Pelican nebulas above, only using the new data to expand the bottom part.  I am surprised how effortlessly and well the stitching worked on these kind of images considering the differences in qualities. All were captured with my 300mm PF and non-modified D7100 on the Skytracker. (Open image in new tab for large version).

[Akira]

The latest image looks more gorgeous, although I may miss the nice blue glow of the two large stars in #1 from the November 13th post.

You used Microsoft ICE for the stitching.  Do you use it on the latest Window 10?  I downloaded the latest version of ICE but am hesitating, because the latest version was released more than two years ago.  When I tried ICE some time ago, it was clearly inferior to Photomerge.  But Tony Northrup says it performs better than Photomerge, so I wanted to try it again.

[Øivind Tøien]

The latest image looks more gorgeous, although I may miss the nice blue glow of the two large stars in #1 from the November 13th post.

You used Microsoft ICE for the stitching.  Do you use it on the latest Window 10?  I downloaded the latest version of ICE but am hesitating, because the latest version was released more than two years ago.  When I tried ICE some time ago, it was clearly inferior to Photomerge.  But Tony Northrup says it performs better than Photomerge, so I wanted to try it again.

Thanks for the comment Akira. I am sort of with you about the blue glow around the stars being sort of pretty although it might be an artifact (image a bit oversaturated). I still wonder if that flare comes from the atmosphere or if there is some interaction between the PF elements and the low pass filter of the D5100 - might need to set up some tests. Unfortunately that image is pretty noisy and also shows some wandering noise patterns.

I am still running Windows 7 on my computer, and my version of ICE is pretty old, from 2015 and seems to be the most recent one, as there is no message about available update on start. It is so quick to use, just drop the images on to it, no sorting or reference points needed. It can even fill in missing pieces, like part of the sky. I have hardly any trouble with landscapes if properly captured - I have even used it with my 10.5 mm fisheye.

[Akira]

Thank you, Øivind, for the details.

You seem to be using the latest version (2.0.3) which was, according to the download page, published more than three years ago:

https://www.microsoft.com/en-us/download/details.aspx?id=52459

But it seems to work on Windows 10.

I haven't been aware that PF elements could interfere with the low-pass filter.

[Øivind Tøien]

I haven't been aware that PF elements could interfere with the low-pass filter.

They might not, it is just an untested hypothesis. (I imaged another night that seemed just as hazy of the same area with D7100 and there seemed to be less flare.) Could well have been differences in haze in the sky, but need some more controlled testing.