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Posts Tagged ‘Cygnus’

NGC 6888 Narrowband (plus some PixelMath)

September 29, 2013 Leave a comment

Finally, some color images!  (Or at least false color.)

This is one panel from my earlier Crescent Nebula 4-panel H-alpha mosaic, with OIII and SII data added.  The first version is in a slightly modified “Hubble” narrowband palette (R=70% SII+30% H-alpha, G=100% H-alpha, B=100% OIII).

NGC 6888 in Hubble Palette

NGC 6888 in Hubble Palette

Image data:
Exposures: 13 x 1200s Ha, 16 x 1200s SII, 18 x 1200s OIII (Total exposure time: 15 hours, 40 minutes)
Software: guiding by PHD, stacking in DeepSkyStacker
Processing: PixInsight 1.8
Telescope: Takahashi FSQ-106ED (530 mm f/5)
Camera: SBIG STL-11000M with Astrodon 6nm narrowband filters, 2×2 binned
Mount: CGEM
September 16, 17, and 28 2013

PixInsight allows you to easily blend and mix images or color channels to create alternate palettes, so let’s use this image as a simple example.  Consider the following simple PixelMath parameters.

PixelMath

PixelMath refers to the color channels in an RGB image as [0], [1], and [2] respectively.  So this tells PixInsight to create a new image with the:

  • red channel composed of the original green channel
  • green channel composed of 70% of the original red channel + 30% of the original green channel
  • blue channel unchanged

The result is a false color image with a different flavor.

NGC 6888 Red-Green Reversed

NGC 6888 Red-Green Reversed

Lonely little NGC 6888 adrift in a sea of ionized Hydrogen.

September 21, 2013 Leave a comment

This is a portion of a larger H-alpha mosaic that I took while the full moon was out this past week. NGC 6888 is a terrific target for a close-up, but it’s also beautiful in context of the whole “neck” of the swan Cygnus.

NGC 6888 Widefield

NGC 6888 Widefield

Image data:
Exposures: Portion of a four-frame mosaic composed of 63 x 1200s Ha exposures
Software: guiding by PHD, stacking in DeepSkyStacker
Processing: PixInsight
Telescope: Takahashi FSQ-106ED (530 mm f/5)
Camera: SBIG STL-11000M with Astrodon 6nm narrowband filters, 2×2 binned
Mount: CGEM
September 16-20, 2013

Tutorial – Creating contrast in nebula images

November 4, 2012 Leave a comment

Since the weather isn’t cooperating enough for me to capture more images of NGC 7000, let’s use the H-alpha channel image to show a few ways to create contrast in otherwise “flat” looking nebula images.

Here is the image basically right out of calibration, with only a single quick curve applied to stretch it a little.  This is six hours of total integration time (20 minute subexposures).

It’s okay, but nothing stands out.  There nebulosity has no definition.  It’s more like fog than a distant cloud.  Before anything else, the first step is to shrink the stars, because the unsharp mask filter I’ll use in subsequent steps has will exaggerate the stars.  You could move the stars to separate layer, but this is a short example, and that would require another tutorial entirely.  Here, all we do is run the minimum filter (Filter > Other > Minimum) with a radius of 1.  The original image size is about 3100 x 2400, so even the small stars can withstand the Minimum filter at this setting.  Smaller images may need to be resampled to avoid the destruction of smaller stars.

 

A look at the histogram reveals that the image isn’t taking up the full dynamic range, so we’ll use Curves to bring the white point down.  We’ll also subtly shape the bottom end of the curve so we bring up the darkest parts of the nebula at the same time.  This is why I always use Curves instead of Levels, even for simple adjustments.

Now, let’s create contrast between the smaller structures in the image.  The next image shows the results after unsharp mask (Filter > Sharpen > Unsharp mask) with a radius of about 10, a threshold of 3, and a strength of about 150%.  This was done to a layer containing a duplicate of the original image, and the layer was then set to the Soft Light blending mode.  Every image will require different settings, but the beauty of the filter is that you can preview the results as you make adjustments to highlight the details you want.  Because this filter reduced some of the darkest areas around the periphery more than I’d like, I used a layer mask to mask those areas off from the effects of the filter.

 

Things are looking much better.  The edges are better defined now, but I’d still like to create more contrast within the core of the nebula.  So I’ll duplicate the image again to a new layer and apply the unsharp mask again, this time with a radius of 90 pixels.  This creates contrast across larger structures.

 

Finally, it’s time for one more application of curves.  I’m still not happy with the contrast across the body of the nebula.  A subtly shaped curve will allow me to choose the areas I want to differentiate.  By holding down on control while clicking the image, I can create anchor points, shown below as A, B, and C.

 

 

The image is in pretty good shape now, at least for a monochrome image:

Now, let’s hope the skies clear so I can capture some S-II and O-III images to combine with this one!

The Western Veil Nebula and Pickering’s Triangle

September 19, 2012 Leave a comment

If Cygnus would stay in the sky all year, I don’t know if I could exhaust all of its imaging possibilities.  This is the Western Veil Nebula, NGC 6960 and Pickering’s Triangle (bottom left). Both are remnants of a supernova from about 5,000 years ago that also includes the beautiful NGC 6888 (not shown) among others.  This nebula is surprisingly bright in all three major narrowband lines, H-alpha, S-II, and O-III, which meant that I could capture a reasonable amount of data in a single night.

NGC 6960 in narrowband

NGC 6960 in narrowband

Image data:

Exposures:  9 x 600s Ha , 10 x 600s O-III, 9 x 600s S-II (6h 40m total), binned 2×2

Software:  guiding by PHD, stacking in DeepSkyStacker

Processing:  Photoshop CS3, tone mapping using modified Hubble palette

Telescope:  Televue NP101 with 0.8x reducer (at about  f/4.3)

Camera:  SBIG ST-8300M with Baader standard narrowband filters

Mount:  CGEM

September 14, 2012

IC1318, The Butterfly Gamma Cygni Nebula

August 31, 2012 Leave a comment

The constellation Cygnus is awash in nebulosity.  Point your telescope almost anywhere in the constellation and you’ll find something.  The usual suspects are the North America Nebula (NGC 7000), the Crescent Nebula (NGC 6888), and all of the pieces of the Veil Nebula.  But right at the heart of the constellation, at the center of the “cross,” there’s another beautiful area.  The picture below shows the area around the star Gamma Cygni, including IC1318, the Butterfly Nebula.  The whole area is swimming with emission nebulae, so it’s hard to say any single feature is a separate entity, but the Butterfly shape is fairly obvious.  The little open cluster at the top center is NGC 6910, but that hardly seems important given the rest of the image.

IC1318 in Narrowband

IC1318 in Narrowband

Image data:

Exposures:  29 x 900s Ha , 8 x 900s O-III, 8 x 900s S-II (11h 15m total), all binned 2×2

Software:  guiding by PHD, stacking in DeepSkyStacker

Processing:  Photoshop CS3, tone mapping using modified Hubble palette

Telescope:  Televue NP101 with 0.8x reducer (at about  f/4.3)

Camera:  SBIG ST-8300M with Baader standard narrowband filters

Mount:  CGEM

Taken August 13, 14, 16, 18, and 22, 2012 from Whitehouse Station, NJ.

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