Rosette nebula – Samyang 135mm F2 + narrow band filters

On Valentine’s day I did post a picture of the Rosette nebula. What I did not tell you was that it was imaged using the Samyang 135mm F2 lens and my Astronomik narrowband filters (specifically H-alpha and O-III). That final photo was a result of 5 x 5min H-alpha images making up the red channel and 14 x 5min O-III images making up both the blue and green channels. I used the gain setting of 100 (19% gain) on the ZWO ASI178MM-cooled, and sensor temperature at -25 degrees celsius.Now there was a slight problem with the images that Sharpcap captured that night, as there was one half of the image slightly brighter than the other, and if you look hard at that image you would notice it. I gather there was an issue with the settings chosen by the program, and this is supposed to have been resolved. This problem plagued both the 0 gain and 100 gain images, but not the 300 gain ones. Which is why the images below are the 300 gain images. I did take 15 images for each filter, but only 14 were usable for the H-alpha. Exposure time was 120 s.

Images were registered and stacked in Deep Sky Stacker before being integrated using the LRGB module of StarTools.

The brightest subs come from the H-alpha channel, and unsurprisingly the score of the frames are also the highest in this channel.

H-alpha stack - Gain 300, 120s exposure
H-alpha stack – Gain 300, 120s exposure
OIII stack - Gain 300, 120s exposure
OIII stack – Gain 300, 120s exposure
SII stack - Gain 300, 120s exposure
SII stack – Gain 300, 120s exposure

The images below were made from integrating the narrowband stacks in StarTools LRGB module.

Rosette nebula in red
Rosette nebula in red
Rosette nebula - H-alpha (red channel), OIII (Blue and green channel). Gain 300 Exposure 120s
Rosette nebula – H-alpha (red channel), OIII (Blue and green channel). Gain 300 Exposure 120s
Rosette nebula - Red (H-alpha), Green (SII), Blue (OIII). Gain 300 Exposure 120s
Rosette nebula – Red (H-alpha), Green (SII), Blue (OIII). Gain 300 Exposure 120s
Rosette nebula - Hubble pallete Red (SII), Green (H-alpha), Blue (OIII). Gain 300 Exposure 120s
Rosette nebula – Hubble pallete Red (SII), Green (H-alpha), Blue (OIII). Gain 300 Exposure 120s

I am pleased with my first successful attempt at imaging in narrowband. I am still considering which is the best setting for imaging with the narrowband filters (Gain 100 & 5 min, Gain 200 & 3 min or Gain 300 & 2 min), lower gain for less noisy images but longer exposures or higher gain with noisier images but ability to take many more exposures to stack to reduce the noise. Decisions, decisions.

Boon