Astrophotography is full of complicated techniques, but the actual workflow doesn’t have to be intimidating. In this post, I’m going to walk through a basic description as to how I process my narrowband images using the Tulip Nebula (Sh2‑101) as an example. This is a beautiful emission nebula in Cygnus, rich in hydrogen‑alpha (Ha) and faint oxygen‑III (OIII) structures.
This isn’t meant to be a universal guide — it’s simply the method that works for me, and the one I used to produce my most recent Ha master of the Tulip.
It is in black and white because only one color (red) has been imaged so far... This will eventually become the red part of the final image after all of the colors are imaged.
For this project, I captured:
That gives me a little over 2 hours of Ha, which is plenty for this target. The Tulip has strong Ha emission, so even a couple hours produces a clean, detailed master with good structure.
I’ll be adding OIII on a moonless night, since the OIII signal in the Tulip is faint and easily washed out by skyglow. These Ha frames were taken during a full moon.
Untouched stacking result
This is actually what I initially have to work with. You cant see the nebula whatsoever, and only a few of the brighter stars, but as you read on, everything I need is actually in this image, and I'll explain how to bring out the stuff you cant see here.
The next thing I do is to bring this image into photoshop, and using the levels adjustment, I'll increase the brightness so I can just barely see the brighter parts of the nebula. This initial stretch also brightens the stars substantially without blowing them out and bloating the stars. This is what I end up with:
Initial stretch
This image is then processed in Starnet. Starnet will output an image with the stars removed, but keeps the rest of the image intact. This allows me to process the nebula separately without the stars, which eliminates star bloat. I now have 2 images, the original image with the stars and one without. I stretch, sharpen lightly and reduce noise- there's always some... until I get something like this:
Starless image processed
Once the starless image is looking close to how I want the nebula, ill add the stars. To do that, I'll copy the image that I fed into Starnet as a new photoshop layer and set the layer mode from normal to lighten. A lot of guys like to change it to Screen, but I find that adds a lot of overall brightness and adds noise which I'll have to remove later.
Once the stars are copied, I'll then slightly crop the image to eliminate any dark border that usually happens because of the initial imaging run. This is a very tiny crop to get rid of the extreme outside of the frame.
Then I make some fine adjustments to the top layer, which is the star layer to brighten the stars to where I like how the stars look in the image, kinda like this:
Stars re-combined
From here, I will make mostly minor tweaks to the entire image. Maybe a little more brightening, maybe a little more contrast enhancement, possibly a curves adjustment to pull out a little more of the very faint nebulosity. These tweaks are usually pretty small, slight changes. Possibly some noise reduction in Camera Raw filter, etc. The goal is to end up with something that looks like this:
Final Ha image
Notice I rotated the image in the final processing. This last image has its orientation with North up. As you can see, this image really isnt too much different from the previous image, as all the big enhancements were done before the starless and the stars merge.
This image I consider ready for some Oxygen and RGB star color frames to be added. I do not have those taken yet, and will do soon my next imaging run.
I should also mention that not only did I capture the nebula, but I also got the area near a fairly nearby black hole. Of course, a black hole cannot be imaged directly, but this is a black hole with astar orbiting it, and I did get the star in the image. That system is cataloged as "Cygnus X1".
Here is an image with an arrow pointing to that system.
0 comments:
Post a Comment