Author Topic: [Theme] Night sky shots  (Read 29322 times)

Řivind Třien

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Re: Night sky shots
« Reply #30 on: March 16, 2016, 11:46:37 »
Then on to a couple of galaxies.
The closest neighbor to the Milky Way system, the Andromeda Galaxy is large and easy to find. Here is a stack of 36 frames at 60 sec with the  300mm PF at f/4.5, ISO 1600, slightly cropped. I tried some different stacking methods, however the examples are not comparable as colors and curves were adjusted independently for each image, so they just shows variation of results with different processing. Which one do you prefer?

In the first one I let Deep Sky Stacker (DSS) digest the raw files,used a median stacking parameter, and supplied some flat frames to compensate for vignetting.




This next one I believe also is based on raw files in DSS.




For this one I converted files to TIFF in CNX2 before stacking. Noise levels might be a bit better, but compensation for vignetting is not as accurate in CNX2 so I ended up combining that with supplying flat frames to DSS treated the same way.




A different processing of the Tiff based stack, showing the core of the galaxy (which consist of a star heap hidden within the "fog")




On location. Light pollution was also subtracted in this shot, so it was a lot less dark than it looks.





I also had a go at the smaller Whirlpool Galaxy from the more light polluted location of my cabin. Clouds were drifting in and out of view so I had to dispose of a number of frames, stack of the remaining 28 frames, 30 sec with 300mm PF at f/4, ISO 1600. First the whole frame with the tiny galaxy to the right. I used the outermost star of the Panhandle (Carl's Wagon/Big Dipper/Ursa Major) as reference thus location of the galaxy at the periphery.

\


Then the heavy crop. The stars have a distorted shape which is likely due to coma of the wide open lens, also possibly in combination with non-optimal focus/atmoshere. I think I will stick to f/4.5 for future exposures.




I also had to try this in IR. Light pollution is much suppressed in IR, but how much IR radiation would reach us from this far away galaxy though our atmosphere? Here is a heavy crop of a 7 image stack at approximately 3 minutes for each exposure (released with IR control), D40x IR 720 and 300mm PF at f/4 and ISO 1600. I used both dark exposures and flats when stacking these shots.

Řivind Třien

BW

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Re: Night sky shots
« Reply #31 on: March 16, 2016, 16:16:46 »
Very impressive! I've tried the same thing several times, but it seems like I am doing something wrong with DSS. I also had some problems with aligning the shots. More reasearch needed. Wind is also a problem where I live. Clear sky is very often associated with irregular gusts of wind and of course low temperatures. All these problems are possible to circumvent, but unfortunately I have not been able yet. Your results tells me that its certainly worth another try :)

Jakov Minić

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Re: Night sky shots
« Reply #32 on: March 16, 2016, 16:19:51 »
Řivind, I am left speechless!
The whirlpool galaxy... amazing!
Free your mind and your ass will follow. - George Clinton
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Akira

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Re: Night sky shots
« Reply #33 on: March 16, 2016, 22:03:09 »
Řivind, this is truly breathtaking series!  I feel the universe much closer than I've always felt.  Especially beautiful are the whirlpool (or crashing or going-by) galaxies.

Of course, I've seen NASA images of these galaxies in much higher resolution and quality, but the fact that you captured them using some "common" camera and lens makes me so excited.
"The eye is blind if the mind is absent." - Confucius

"Limitation is inspiration." - Akira

BW

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Re: Night sky shots
« Reply #34 on: March 16, 2016, 23:26:23 »
When looking up into the night sky, it hard to believe that there is not some kind of intelligent life out there. Since it´s not down here I mean...

Jakov Minić

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Re: Night sky shots
« Reply #35 on: March 16, 2016, 23:53:01 »
Sprinkles?  8)
Great idea, Břrge!
Free your mind and your ass will follow. - George Clinton
Before I jump like monkey give me banana. - Fela Kuti
Confidence is what you have before you understand the problem. - Woody Allen

Řivind Třien

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Re: Night sky shots
« Reply #36 on: March 17, 2016, 02:01:30 »
Very impressive! I've tried the same thing several times, but it seems like I am doing something wrong with DSS. I also had some problems with aligning the shots. More reasearch needed. Wind is also a problem where I live. Clear sky is very often associated with irregular gusts of wind and of course low temperatures. All these problems are possible to circumvent, but unfortunately I have not been able yet. Your results tells me that its certainly worth another try :)

Thanks for the comment Břrge. It takes some time to wrap ones head around DSS as there are so many settings (I am still working on it), and it is not always clear what they are doing. There are some tutorials out there; search for  "deep sky stacker tutorial" and the first one is a video going though the basic settings. The starting point with accurate alignment of the tracker using a polar scope and correct exposure with histogram between 1/4 and 1/3 is also crucial. It is best to keep ISO in the 800-3200 range (typically 1600) depending on the body, as post sensor electronics noise dominates above sensor read noise at too low ISO and if too high, dynamic range is reduced. (Some Nikon sensors may tolerate lower ISO well though).

Wind may or may not be a problem - the Andromeda Galaxy image was captured on a pretty windy day (relative to Fairbanks...). For the shots above I went though the images manually before stacking and discarded the ones that had trails either because of wind (less of a problem) or periodic error of the worm drive. DSS is able to automate sorting but I have not tested it yet.

There are lots of general information and really nice images at Roger Clark's pages starting at the top at  http://www.clarkvision.com/articles/nightscapes/. He expresses some interesting views on format of image sensor vs. noise, and he is a proponent of processing images for natural colors by subtracting light pollution (as that is an addition to light) rather than changing white balance (gains) to compensate, which will screw up the colors of stars. 
Řivind Třien

Řivind Třien

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Re: Night sky shots
« Reply #37 on: March 17, 2016, 02:20:13 »
Thanks for the kind comment Jakov.

Řivind, this is truly breathtaking series!  I feel the universe much closer than I've always felt.  Especially beautiful are the whirlpool (or crashing or going-by) galaxies.

Of course, I've seen NASA images of these galaxies in much higher resolution and quality, but the fact that you captured them using some "common" camera and lens makes me so excited.

Thanks Akira, yes when getting into this it was pretty clear to me that there are always someone out there with much better equipment that have already created much nicer images, and not to mention the Hubble space telescope images. So it is in many ways a personal journey and experience than being able to top the best out there. However the images one are able to get today with a DSLR from the last few years and standard lenses might actually be as good as results gotten in pre-digital or early digital age with large diameter telesopes. Just look at the link to Roger Clark's page above and some of the links he provides. It is also interesting how much variation there can be in expressions just because of processing.
Řivind Třien

Řivind Třien

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Re: [Theme] Night sky shots
« Reply #38 on: April 08, 2016, 11:04:56 »

First sucess on Pinwheel galaxy - M101


Finally I got in >2 hours of imaging time (red zone) on another galaxy, M 101, the Pinwheel Galaxy, resulting in 110 exposure totaling ca 1 hour 50 minutes of usable frames (60s exposures at ISO 1600, D7100/AFS 300mm f/4 E PF @ f/4.5 on Skytracker) before aurora took over. Stacked in DSS using 2x drizzle - the image is a little less than half the width of the original frame.

I wonder what the "cloud" in the lower left of the frame is, could it be another galaxy/nebula or is it some kind of flare/ghost artifact? I could not find anything like it at that location in Stellarium (best viewed large).
[Edit: A quick reponse from Russ (RustierOne) at DPreview identified it as "spiral galaxy NGC 5474, magnitude 10.8, 4.7' x 4.7', 22 million lightyears distant." He also mentioned that I caught "another galaxy at about the 10 o'clock position from M101 - its NGC 5477, magnitude 14.0, 1,6 ' x 1.3'  ".]


M 101 with AFS 300mm f/4 E PF @ f/4.5 on Skytracker, 60s exposures, 110 used.



My first attempt at M101 a week before was not successful, but I sort of like the result  :) . Strangely, none of the single frames that were stacked have such a pronounced auroral pattern before stacking.


M 101 buried in aurora with AFS 300mm f/4 E PF @ f/4.5 on Skytracker, ca. 40 30s exposures used, most of the frame.


I also got another go one the Whirlpool Galaxy (M 51) the night before, but got only 30 usable 60 sec frames before aurora took over (2x drizzle in DSS).


M 51 with AFS 300mm f/4 E PF @ f/4.5 on Skytracker, 60 sec exposures @ ISO 1600, ca 30 usable.


Aurora burying the target.






Another elusive targets are nebulas radiating in the hydrogen alpha range. Typically, converted cameras are used for these, but it is still possible to get to it with a standard body if the sky is dark enough... As a physiologist I had to make an attempt at the Heart Nebula - in the light polluted red zone..., targeting got a bit off so I only got the atrium and the very top of the ventricles in bottom half of the frame; aurora lingers at the very bottom of the frame. I believe the "aorta" is the red spot to bottom right. I kept it mostly because of the stars.

As a side note, while capturing exposures for this over 80 minutes I heard telltale sounds of a moose browsing out in the dark and moving at regular intervals. Soon I could see a dark shadow 40 meters away, and I envisioned the moose trampling down the tripod with Skytracker and my dear 300PF. So I for much of the time I kept close to it  in case of need for an emergency evacuation, which may have disturbed the tripod and caused less successful tracking than normal (I usually keep a good distance to the tripod).

 
AFS 300mm f/4 E PF @ f/4.5 on Skytracker, 60s exposures, ca. 25 used.

Again Aurora took over...
I have started to experiment with treating aurora images the same way as the star images: Rather than changing white balance I subtract light pollution, and in this case some overly green cast, with a levels step (adjusting each channel separately) in CNX2. This seems to preserve more natural background star colors.



Řivind Třien

Erik Lund

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Re: [Theme] Night sky shots
« Reply #39 on: April 08, 2016, 12:08:29 »
Řivind, thants for posting this information and images, wow - Fantastic resoults with an affordable pricetag!
Erik Lund

Řivind Třien

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Re: [Theme] Night sky shots
« Reply #40 on: April 08, 2016, 14:08:02 »
Thanks  for the kind words Erik.

BTW, here is the current status of my rig after I added a red dot sight and another right angle finder.


(The essential intervallometer not connected here for less clutter).

The red dot sight allows accurate aiming without aligning the eye and allows a wide view around the point of interest (no magnification), essential when one only can see the brightest stars to navigate by. The center of the cameras viewfinder was aimed at the top of tree looking though the 300PF+TC-14E.
Řivind Třien

armando_m

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Re: [Theme] Night sky shots
« Reply #41 on: April 08, 2016, 14:39:02 »
Řivind

Thanks for sharing all this information, the shots are literally out of this world !

the skytracker sound like a great little gadget and not at all expensive compared to other alternatives
Armando Morales
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Řivind Třien

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Re: [Theme] Night sky shots
« Reply #42 on: April 10, 2016, 12:02:06 »

Thanks for the kind comment Amando.
Yes I am having a lot of fun with the tracker and have been trying to use every opportunity lately as once the moon takes over this month there will be no really dark skies before autumn.

Last night I made another attempt at the Whirlpool Galaxy (M 51), which I managed to get perfectly centered this time using the red dot sight to navigate relative to the two outer stars of the "Panhandle". I originally got 194 captures, each 60 sec @ ISO 1600 before the first signs of dawn, however once I downloaded the files I discovered that light clouds had periodically gotten in the way causing light pollution to kick in strongly on those frames. After culling that included satellites that mysteriously tended to pass almost right in front of the galaxy and clear mis-tracking, 86 remained. I asked DSS to stack 95% of those = 82 minutes total exposure. With more frames collecting light, it seems that both noise and detail has improved since last attempt; this is my fourth try on M 51.


Whirlpool Galaxy M51 with AFS 300mm f/4 E PF at f/4.5, 82 x 60 sec, ISO 1600, 2 x drizzle in DSS.
Řivind Třien

ColinM

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Re: [Theme] Night sky shots
« Reply #43 on: April 10, 2016, 22:36:41 »
Řivind
, the shots are literally out of this world !

Couldn't have said it better.
Armando, I loved both versions of your Milky Way moonrise, though in the second one the reflection of the moon on the water starts to gain more prominence than suits the rest of the image.

As for Ovind's images, I can't believe these were taken with a 300mm and a DX camera! I've only previously seen images of galaxies taken with telescopes. I've used Zerene to stack macros, but have no experience of DSS - is that & the stacking getting you this level of magnification/resolution?

Řivind Třien

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Re: [Theme] Night sky shots
« Reply #44 on: April 10, 2016, 23:29:47 »
As for Ovind's images, I can't believe these were taken with a 300mm and a DX camera! I've only previously seen images of galaxies taken with telescopes. I've used Zerene to stack macros, but have no experience of DSS - is that & the stacking getting you this level of magnification/resolution?

Thanks for commenting Colin. The main purpose of stacking in DSS is to reduce noise by several different choices of averaging/stacking methods. This will allow to pull up fainter subjects that otherwise would be buried in noise. In the image above I also used 2x drizzle which will take advantage of small imperfections of alignment and tracking to create an image with 2x as many pixels in each direction (but due to memory restrictions it can in practice only be applied to initial crops to half of the frame which is selected in DSS). I guess this is a little like the pixel shift in later Pentax bodies to create higher resolution, but it requires a large number of frames to be effective. Compare the image of the full frame in the first of my posts in this thread, and also the last one to the one before which also used 2x drizzle, but with fewer captures. Yes, it is quite amazing what standard equipment, inexpensive accessories and free software can get us these days, results that required larger telescopes and heavy equipment decades ago. That is what makes it fun, and one can keep improving on imaging the same subjects.
Řivind Třien