Sunday, November 8, 2015

Sharpless 132 - my first unguided image

Sharpless 132 is an emission/dark nebula in Cepheus:
(click on image for full resolution)

It is about 10,000 light years away from earth in the Perseus arm of the Milky Way. It's ionized by two Wolf-Rayet stars: HD 211853 in the middle of this photo and HD 211564 (not visible in this image). Many stars in this nebula are relatively young and of the same age which indicates that they were born out of the nebula - but the process seems to have stopped.

This is my first unguided image. I took 80+ images with only very few that showed star trails. Those were mostly in areas of the sky where I didn't calibrate my model (my horizon in TSX isn't 100% accurate).

This nebula has a lot of fainter regions further out. But those aren't too strong in narrowband but more in visible light. Maybe in the future I will image this nebula again from a darker side with a larger chip.

Thursday, October 29, 2015

Unguided Imaging

Now, where I have my MyT mount back in action, I wanted to try to do some unguided imaging. I spent two nights setting everything up:
  1. Setup the scope - do a rough visual polar alignment
  2. Home the mount
  3. Take an image of the place that the scope points to, plate solve (all sky as the scope will be quite far away from the expected point) and sync the mount to this location
  4. Run a model with 10 points, use this to do a more accurate polar alignment. As the polar alignment will be still pretty far out, I'm using the tics information in the polar alignment tab
  5. Run another model with 10 points, now do the accurate polar alignment
  6. Now run a model with 200 points, create a Super Model
  7. Use this model to improve the polar alignment (it was already very accurate)
  8. Run a 30 point model to realign the model with the new polar alignment
  9. Check polar alignment error - was neglectible
  10. Next, use PEMPro (the beta version with Ascom support!) to measure the periodic error
  11. Add the periodic error to the mount
I did some test exposures and could easily take 10 min exposures without any star trails or elongations!

Next, I wanted to use SGPro - using the DirectMountGuider for unguided imaging. Unfortunately, it didn't perform a Meridia flip. When looking through the log file, I found the following lines:

[10/24/2015 4:27:13 AM] [DEBUG] [Pier Flip Thread] Meridian Flip: Telescope has performed meridian flip).
[10/24/2015 4:27:43 AM] [DEBUG] [Pier Flip Thread] Autoguider (Direct Mount Guider) failed to flip calibration data!
[10/24/2015 4:28:46 AM] [DEBUG] [Sequence Thread] Blocking Pier Flip: Failed to meridian flip, aborting sequence (True)

I sent this to the SGPro forum and got the reply that this will be fixed in the next version of SGPro. And the moment I asked when that will be ... the developers announced the release of the next version. And sure enough, this was fixed!

Monday, September 28, 2015

Lunar Eclipse

The lunar eclipse in San Jose would be very special: the moon would rise just before the full eclipse begins. To capture it, I setup my camera on top of our house:

The day of the eclipse was completely overcast :-( But in the evening it cleared up...
... in the west!!!

Thick, thick clouds in the east. So, here is the best image that I took (including some processing):

Sunday, September 27, 2015

VDB 152 and Barnard 175

(click image for full resolution)

The reddish nebula in this image is Barnard 175 - 1,400 light years away from earth. On top is the reflection nebula VDB 152. Interestingly, the star that causes the reflection is not from the nebula but is just passing through (it's velocity is very different from the nebula's velocity).

Zooming into the reflection nebula:

You can (barely) see two red lines. These are the remnants of a supernova explosion. I should take more Ha data for this image to make these better visible.

SH2-155 - The Cave Nebula

(click image for full resolution)

This image actually contains three nebulae:
  1. SH2-155 (The Cave Nebula) - the bright, red wavefront on the right (discovered by Stewart Sharpless in 1959)
  2. LDN 1215 - the dark nebula on the left (discovered by Beverly T. Lynds in 1962)
  3. VDB 155 - the emission nebula in the upper left corner (discovered by Sidney van den Bergh in 1966)
The whole complex is 2,400 light years away from earth - the dark cavernous are of the cave nebula is 35 light years in diameter.

My field of view is "just" working to get these three objects together - a little more area around it would work good.

With my usual imaging length (10xLuminance, 600sec at 1x1 plus 10xRGB, 450sec at 2x2) I captured quite some detail in the cave itself:

Though at some point in the future, I might take more luminance data to refine this more.

Saturday, September 26, 2015

LDN 1235 - The Dark Shark Nebula

(click on image for full resolution)

This is 5+hours of data (100min Luminance at 1x1, 75min RGB each at 2x2). This nebula is a mix of reflection (the blue tint), Extended Red Emission (the reddish ares) and dark nebulae. But I think for these dark nebulae with structures you need more data. Still there is a lot of detail here - including the blue hue around HD 210806 in the lower left corner.

Processing was tricky - had to be very careful with my CurvesTransformation to make sure that by lowering dark areas, I won't loose too much detail in the nebula. And also when stretching the nebula, no to brighten the background.

As an experiment, I tried to reduce the stars to make the nebula more prominent (using this great tutorial)

The nebula is indeed more prominent, but it looks weird that there aren't any "mid size" stars.

Friday, September 25, 2015

M20 - The Trifid Nebula

(click on image for full resolution)

I wanted to image this nebula for quite a while. But because of it's low declination (it's in Sagittarius) I have to do it from sites with a good view to the south. I started to image it at GSSP (red and blue) and then finished it at my trip to Richards ranch (luminance and green).

Discovered by Charles Messier on June 5th, 1764, we don't know exactly the distance to the Trifid Nebula - between 2200 and 7600 light-years.

It was weird when I first combined and auto-stretched this image I got some weird red artifacts around the stars:

Processing the RGB and Luminance image separately (and blurring the RGB images before applying the Luminance image) fixed this.

NGC 7023 - The Iris Nebula

I used the dark skies at GSSP 2015 to image the Iris Nebula - a reflection nebula that is 6 light years in diameter and at a distant of 1,300 light years distance. The nebula was discovered  on 18 October 1794 by William Herschel:
(click image for full-size)

This image consists of 5+ hours data (100 min luminance and 75 min red, green blue each).

The blue color comes from the young, hot star in the middle (SAO 19158) - it has 10 times the mass of our sun. Zooming into the center of the nebula shows some reddish glow:

This is the result of ultraviolet light (from the center star) converted to visible light.

I found this great sketch on the web that illustrates how we see this nebula:
Title: Structure and physical properties of the bipolar outflow source NGC 7023
Authors: Watt, G. D., Burton W. B., Choe, S.-U., & Liszt, H. S.
Journal: Astronomy and Astrophysics (ISSN 0004-6361), vol. 163, no. 1-2, July 1986, p. 194-203
Bibliographic Code: 1986A&A... 163.. 194W

Tuesday, September 15, 2015

Sharpless 2-112 - a small emission nebula in Cygnus

Took narrowband images of Sharpless 2-112 from our backyard:
(click on image for higher resolution)

It took me a long time to stretch the red (SII), green (Ha) and blue (OIII) to get some of the details out. This image is 18+hours of data (Ha: 2hours, OIII: 6hours, SII: 10hours).

Sunday, September 13, 2015

M33 (Triangulum Galaxy) - Now and three years ago

I imaged M33 - the triangulum galaxy. I needed quite a lot of data (15.5) hours, but it turned out surprisingly well:
(click image for full resolution)

As always when imaging from our backyard, I didn't take any Luminance frames but just RGB (all binned 1x1). Framing JUST worked with the small sensor of the MLx694 camera. I chose my new processing steps:
  1. Gradient removal (using DynamicBackgroundExtraction)
  2. Color Correction (using BackgroundNeutralization and ColorCalibration)
  3. Noise Reduction (using MultiscaleLinearTransformation)
  4. Stretching (HistogramTransformation)
  5. Bringing out faint outer details (using LocalHistogramEqualization)
  6. Bringing out details in the core (using LocalHistogramEqualization)
  7. Sharpening (using AtrousWaveletTransform)
  8. Final adjustments (colors, lightness and saturation) using CurvesTransformation
I like the result a lot!

Almost exactly three years ago, I imaged the same galaxy. At that time with my first scope (Celestrono Nexstar 6SE) and my Nikon D7000. This was the image that I took back then (8x4min):

More data, better equipment and more experience seem to pay off :-)

Barnard 143 - My first dark nebula

I tried to image my first dark nebula: Barnard 143. The dark nebula itself doesn't have any details, i.e. the image only consists of stars and dark areas:

These objects are pretty good for our light polluted backyard! This image has a little over 6 hours of data! Processing was very straight forward (gradient removal, color calibration, stretching).

Bringing out OIII and SII details in narrowband images

Most of the time, the Ha signal in emission nebulae is MUCH stronger then the OIII or SII signal. Take my recent image of SH2-112 as an example:




All these are stretched and look similar in strength. But combining them results in this:

Increasing the red component brings out more SII details but also leads to a very red background:

To avoid that, I extract the luminance of this image:

Using HistrogramTransformation, I Auto zero shadows and highlights and use this as a mask for this image. The same red stretch now results in:

The sky stays dark and more SII details in the nebula. I don't worry about the magenta stars as I will fix them at the end anyway.

Bringing out inner details in Pixinsight: HDRMultiscaleTransform vs. LocalHistogramEqualization

Recently, HDRMultiscaleTransform was introduced in Pixinsight (well, maybe not so recently, but I recently "discovered" it). I used it successfully a couple of times for images to bring out inner details in galaxies or nebulae. But a couple of times, it was way too strong. E.g. here is an image of M33 that I recently took (after most of the processing):

And here I applied HDRMultiscaleTransform (as "low" as possible):

That's WAY too much. Using a mask and using LocalHistogramEqualization:

I can play with the ContrasLimit setting and then with the Amount setting until I bring out just enough details in the galaxy core.

Noise Reduction in Pixinsight: TGVDenoise vs. MultiscaleLinearTransform

In my last images, I started using TGVDenoise last year. This was based on the easy-of-use but also some analysis about its effectiveness. But I often had the problem that it created blobs on the image that were hard to fix.

Here is an example:


After TGVDenoise

I tried a lot, but could never get a smooth background. These blobs can be minimized using the ACDNR process after stretching the image, but I found that too cumbersome and didn't want to make too many changes to the image.

Kayron Mercieca recently published a comparison of the different noise reduction processes and their pro's and con's. Based on the great explanations there, I tried to use MultiscaleLinearTransform:

This looks much better - and thanks to the great explanation in the blog post I even understand now how it works and how I need to adjust it.

So, I guess for now, I'll keep using MultiscaleLinearTransform.

Monday, August 17, 2015

Stars over Ghost Ranch

The night at Ghost Ranch was awesome. Although the rock formations were completely black (I had hoped that they would be just a little bit light up) it made for some amazing pictures:

First, the milky way over Ghost Ranch:

The lights in the lower right corner are from the cities Santa Fe and .

Then, a time lapse of the milky way with some Perseid meteors in it. I used the Vixen Polarie differently this time: I mounted it completely horizontally and set it to 1/2 speed. With this I got an effect that the foreground is also slowly moving:

And finally, the composite of all meteor images (see previous entry how I created it):
(click to see a full resolution image)

Sunday, August 16, 2015

Perseids - my first meteor composite

This year, the peak of the Perseids coincided with a new moon. AND we were on vacation in Santa Fe. Great opportunity to get some images and try my first meteor shower.

I drove 1.5 hours north of Santa Fe to Ghost Ranch.

I started setting up my camera at 8pm. Once it was dark, I took a couple of images for a mosaic of the milky way. Checked focus...


I then setup the camera on top of the tripod and took continuously ISO 6400, 19 sec exposures. I ended up with some 650+ images - and ~50 with meteor trails.


First I had to figure out how to align all images with meteor trails. I selected one that was in the middle of the sequence as the background.

My first attempt was to align all images with the StarAlignment process in Pixinsight. Only very few images could be aligned. As soon as the image was too far away (~20 minutes) from the background image it failed. The reason seems to be that a) there wasn't much overlap, but b) the 14mm focal length creates a lot of distortion in the corners.

Next, I tried "2-DSurface Splines" as the Registration Model in StarAlignment. It's suitable for much larger distortions in images. With this I could align 23 of the images.

Next, I created 1000x1000 subframes of meteor trails that couldn't be aligned. With that, I could align another 15 images.

But several of the remaining images contained meteor trails that we still inside the background frame - they were just too much distorted. For those frames, I used the DynamicAlign process in Pixinsight. It took me a while to figure out how it works:

These two images have some overlap and the meteor trail of the second image is clearly in the first one:

After opening the DynamicAlignment process, you have to select the primary (background) and the secondary image (meteor trail):

Now, DynamicAlignment works by mapping stars from one image to the other. First, I select the bright star at the tip of the meteor in the first (background!) image:

Pixinsight has no knowledge yet of any distortion, relation... between the two images, so it puts this point in the second image just near the X/Y coordinate of the first image:

I drag this indicator with the mouse up to the correct star in the secondary image:

Now, I can enlarge the second image to position the star correctly:

And now I zoom the first image to a similar scale and position in the image:

Now, I click on bright stars next to the first one. Every time, Pixinsight highlights the star in the second image that it thinks maps. As soon as it gets it wrong, I correct it in the second image. After a few stars, Pixinsight gets an idea of the distortion between the two images and gets almost every star right. I orient myself on the second image and click many stars around the meteor trail:

Once I think I have enough stars, I click the green "Execute" check mark and create a registered image:

It's easy to check the alignment (just putting the registered image on top of the background image and switching between the two). You get star alignment pretty quickly (30+ alignment stars). But when you look at the registered image, you can see that the meteor trail is not straight anymore!! Pixinsight calculated a transformation based on the clicked stars that resulted in this. This can be fixed by clicking on more stars near the area where the meteor trail is curved.

With this, I could align 6 more meteor trail images!

This brings the overall number of meteor trails to 44!

Merging all images

Similar to my star trail image, I want to merge all the images using Layers in Photoshop and Lighten blending mode.
... and immediately run into the first issue:

Many of the full frame images have the tree and mountains in them! Well, with a little bit of effort, I crop them out. Unfortunately, you can't easily crop a layer-only (crop is only for the full image), so I ended up just cutting out the non-sky areas of an image:

Which results in this image:

Still no luck - a lot of the images overlap with the ground and the sky background isn't even across all the images. So, I'm using the lasso to cut out smaller areas around the meteor trails:

Better, but the different background levels still make it bad. I tried a little bit to lower the backgrounds around the meteor trails, but especially the fainter trails would get even fainter. So, I ended up cutting out all the meteor trails with the magic wand (using high tolerance in areas where the meteor trails is very bright, and much lower (down to 2) in areas where it is very faint):

Doing this carefully for all meteor trails, I finally get this merged image:

Final Processing

I find processing in Lightroom easier then in Photoshop. It has all the features that I need but is much simpler.


First, I adjust the temperature to have less blue:

Then I use Dehazing to get more detail:

Dehazing seems to shift the white balance into the blue again, so I correct it again:

Next, I remove the vignetting in the corners:

Clarity to increase detail:

Turn down vibrance a little to give it a more natural look:

Increase Saturation slightly to bring out the colors:

Lower the Exposure just a little to darken the image:

Increase Highlights to bring out the stars, meteor trails and milky way:

Decrease shadows to darken the background and sky:

Finally, white clipping

... and black clipping to bring out more details:


This is the final result:
(click on image to get a higher resolution view)

Not too bad for a first one ...