I had an opportunity to image the Cone nebula and Christmas tree cluster in narrowband recently using the Samyang 135mm F2 lens. In total I had taken 25 x 3 min H-alpha, 24 x 3 min O-III and 20 x 3 min S-II subs for stacking (total 3hr 27 min exposure). I used Gain 200 on my ASI178MM-cooled @ -25 degrees Celsius.
Nebulosity 4 was used to capture the sub frames and also to pre-process with dark and flat frames. These were then aligned and stacked with Deep Sky Stacker, as they did not align well with Nebulosity. I then combined these in Nebulosity to create an RGB image – H-alpha for red, O-III for green and S-II for blue channels.
The final image is below.
I did notice something interesting in the top right of the image. Turns out that it is the Hubble’s variable nebula NGC 2261, which is a 9.2 magnitude nebula measuring 4.0 x 2.0 arcminutes in size.
For narrowband imaging, I think I am happy with the gain setting of 200, as it allows me to image using 3 minute subs and grab enough light for stacking. With the shorter subs, it does allow me to capture many more images for stacking. I think I’m starting to get the hang of imaging, stacking and processing narrowband images.