Deep Sky RGB filter – Pleiades and Rosette nebula

In the recent months, each time when there was clear skies, there seemed to be the moon prominently lighting up the night sky. Hence the only form of imaging I could do was with narrowband filters. But recently there were a few reasonably clear nights without the moon lighting up the sky. So even though the light pollution was higher than it normally is, I decided that I still had to take the opportunity to try out the Astronomik Deep Sky RGB filters for imaging.

Equipment used:

ZWO ASI178MM-cooled imager, Geoptik EOS-T2 adapter, Samyang 135mm F2.0 lens, Astronomik Deep Sky RGB filters, Astronomik CLS-CCD filter for luminance channel, TS 8×50 Finder scope with Lacerta MGEN autoguider, iOptron ZEQ25 mount.

For the image capture I used F2.0, Gain 200 30 sec subs for all channels. So in total I captured 20 x 30 sec subs for R, G and B channels, and 30 x 30 sec subs for Luminance channel. I decided to guide even for such short exposures as it is so easy with the finder scope and Lacerta MGEN. These images were stacked individually into their respective channels in Deep Sky Stacker before the various LRGB images were combined together in StarTools to form the final image.

Below are the screen grabs for each of the channels to show that the left shoulder is not clipped and there is only minimal clipping of the right shoulder of the histogram. So it looks like this is the ideal setting for LRGB capture with my Samyang 135mm F2.0 lens. With an F4 telescope, I will likely have to image with Gain 200 2 min subs (4 x longer exposures) in order to get the same histogram curve.

Now I did notice that the stars in the red channel for Pleiades were not round, and that is likely as I had not seated the filter properly when threading it into the Geoptik EOS-T2 adapter; this means I will need to reshoot the red channelon another day after fitting the red filter in properly to try and get better subs for combining.

Screen shot of Red channel
Screen shot of Red channel
Screen shot of green channel
Screen shot of green channel
Screen shot of Blue channel
Screen shot of Blue channel
Screen shot of luminance (CLS-CCD) channel
Screen shot of luminance (CLS-CCD) channel

And the final combined image, which should be better if I had better red channel data, as I am not really happy with the stars. But at least I know the right settings to use now. Do bear in mind that Pleiades was very low down and hence I do expect better images with DSOs higher up in the sky.

Pleiades - LRGB using Astronomik CLS-CCD (L), Astronomik Deep Sky RGB filters.
Pleiades – LRGB using Astronomik CLS-CCD (L), Astronomik Deep Sky RGB filters.

I also managed to capture the Rosette nebula in LRGB for stacking over a 3 day period. It was also fairly low down in the sky, so not ideal for capturing these images. But I wanted the opportunity to test out the Deep Sky RGB filters.

Rosette nebula - LRGB using Astronomik CLS-CCD (L), Astronomik Deep Sky RGB filters.
Rosette nebula – LRGB using Astronomik CLS-CCD (L), Astronomik Deep Sky RGB filters.

Now I have not done much LRGB imaging up until now, as unlike others I started with narrowband imaging owing to the prevailing sky conditions with prominent moonlight. So in a sense I learnt the hard way how to do mono imaging.

But with the Astronomik Deep Sky RGB filter set, I did not adjust the colour ratio of each channel when stacking the LRGB channel images together, as this is supposed to be one of the great features of this filter set. I’m sure as I learn to image with LRGB, I should be able to get even better results.

Boon