M20 The Trifid Nebula taken with Narrow band filters.
Ballard
Loc: Grass Valley, California
I have recently started to play with Narrow band imaging to see what it can show. In my latest attempt I imaged M20 (Messier object 20 the Trifid nebula) in Sagittarius. For this image I used 3 different 5 nanometer narrow band filters (Hydrogen Alpha (Ha), Oxygen 3 (OIII) and Sulfur 2 (SII) filters), to take 3 sets of images (one each filter).
The images where taken with an 11 megapixel Cooled CCD camera connected 16 inch Schmidt Cassegrain telescope at F10 (~4000mm focal length). Each set contained 16 images and each image was a 15 minute exposure for a total exposure time of 12 hours across the 3 sets. Each individual set was stacked together to improve the single to noise of each filter used. I also used Dark frames, Flat frames (different for each filter) and bias frames. To combine stacked images from each filter type into a full color image I used what is known as the Hubble Palette where SII is assigned to the red channel, Ha to the green channel and OIII to the blue channel. This creates a "False Color image", however the channels are picked this way to make it easier to see the composition of the nebula. On initial combination the nebula was very green and I had to greatly reduce the green to see the other colors come out, which is expected since the nebula is mainly hydrogen gas that was assigned to the green channel. The colors show some of the chemical composition of the nebula, the yellow through red show the ionized sulfur, the aqua through blue shows the ionized oxygen. Although I greatly reduce the green, the hydrogen signature still comes through as the orange to yellow color coming from the combination of the red from the sulfur mixed with the green from the hydrogen. Likewise the the aqua color being a combination of green and blue with the blue from the ionized oxygen and the green from the hydrogen. (Note: I'm using the color names in a loose fashion here as they are a bit arbitrary since the color assignment is not the real colors emitted by the elements in the nebula but only used to make easy to see the different components of the nebula). The first image is of the full nebula taken at a 4000mm focal length. The second image is a cropped version of the first image centered on what has been called the unicorn nebula inside the Trifid nebula. The second version has also been contrast enhanced to try and bring out more detail. For those interested last year I posted an image of the Trifid nebula taken with a DSLR at
https://www.uglyhedgehog.com/t-652657-1.htmlThe image taken with a DSLR is what the nebula would look like to our eyes if they where sensitive enough.
All questions comments and suggestions are welcome.
The Trifid nebula using narrow band filters to create a False Color image using the Hubble Palette.
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Zoomed in section of the nebula (if you squint just right you can see the head of the unicorn).
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I am so involved in studying about the vastness of the Universe that this amazing image just hits home. Beautifully done with incredible technique! Thank you for posting.
Ballard
Loc: Grass Valley, California
Hi angler
Thanks for checking out the narrow band image of the Trifid nebula and for the comment.
Ballard
Loc: Grass Valley, California
Julian wrote:
I am so involved in studying about the vastness of the Universe that this amazing image just hits home. Beautifully done with incredible technique! Thank you for posting.
Hi Julian
Thanks for viewing my latest try at astrophotography and for the comment. I also enjoy learning about the universe in which we live.
Ballard
Loc: Grass Valley, California
nimbushopper wrote:
Well done!
Hi nimbushopper
Thanks for viewing the narrow band image of M20 and for the comment.
Ballard
Loc: Grass Valley, California
Hi Irvingite Charles
Thanks for checking out my narrow band image of the Trifid nebula and for the Thumbs up.
Ballard
Loc: Grass Valley, California
dpullum wrote:
It is interesting that "Narrow Band Filters&q... (
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Hi dpullum
Thanks for viewing my newest image of the Trifid nebula using narrow band filters and for the all the info links and the comment. There narrow band filters I use don't completely eliminate light from other elements and molecules as they are 5 nanometers wide but do tend to indicate the predominance of the those elements they are targeted for. To get details would require a real spectroscope to see all the individual lines, these devices are available to the armature market, of course they don't produce an image of the object only the spectra which can be used to get a much better idea of the elements available. The narrow band filter like I am using can show structure details in the object that might otherwise be hard to see.
Ballard
Loc: Grass Valley, California
Hi Longshadow
Thanks for the Thumbs up and for checking out the image of the Trifid nebula.
Fantastic photo. I am curious as to how the picture has no movement on the stars with a 15 minute exposure.
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