Feedback Wanted

[Somerled7]

I've been spending the last couple of months getting together some kit (mainly a new scope Altair Astro 72EDF) and learning about polar alignment and plate solving using Sharp Cap and Astro Tortilla.  I've finally got some extended time on a subject - The Pelican Nebula.  My sky quality is Bortle 5 (Artificial Glow around 900MicroCD/m**2 according to Clear Outside).

Scope: Altair Astro 72 EDF#

Camera: Canon EOS 80D (unmodified)

Filter: Astronomik CLS 

40 x 300s Light ( 3hr 20mins)

22 x Darks+ Flats and Bias

Stacked in Deep Sky Stacker and processed in Photoshop.

I'm mainly interested in feedback on the processing.  After stacking, I've done some curves stretches in Photoshop whilst in 32 bit mode, then switched to 16 bit and adjusted the background colour using levels adjustments on each channel.  A few more stretches, then some cosmetic edits to highlights, contrast clarity  etc in Camera Raw, and finally some noise reduction using Topaz Labs.  I feel I have a lot of noise/grain in the image and maybe I've tried a bit too hard to hard to pull out detail that isn't really there!  Any feedback welcome.

[steppenwolf]

At first glance, this is a very colourful image but you are, unfortunately, right about the noise and I do wonder if some of your noise reduction process and colour adjustments have destroyed detail in the image. Sometimes a more laissez-faire approach can produce a more natural image.

Would it be possible for you to upload a 16 bit .PNG file showing the image after you have done the switch to 16bit mode but before you have carried out any noise reduction/colour adjustment?

[Somerled7]

7 hours ago, steppenwolf said:

At first glance, this is a very colourful image but you are, unfortunately, right about the noise and I do wonder if some of your noise reduction process and colour adjustments have destroyed detail in the image. Sometimes a more laissez-faire approach can produce a more natural image.

Would it be possible for you to upload a 16 bit .PNG file showing the image after you have done the switch to 16bit mode but before you have carried out any noise reduction/colour adjustment?

Hi Steve, PNG file attached. I've done a few stretches to lift the histograms, but that's all - the image has a strong turquoise cast due to the CLS filter.  looking at the colour channels, the red already shows a fair bit of noise, but unfortunately that's the channel with the nebula detail.  The blue and green channels look cleaner, so I'm thinking the filter has cut out a lot of red and pushed what's left down into the noise.  Maybe I'd be better without the filter and handle the light pollution in post processing, but I thought the CLS filter was intended for emission nebulae?

    

 

[steppenwolf]

Thank you - looking into it to see what is going on!

[steppenwolf]

I think that your CLS filter is perhaps giving you more problems than it is solving and the strong blue hue is overpowering the red making it hard to recover the signal. In my own quick processing run, the noise developed very quickly indeed.

It would be very interesting to see the results obtained from using no LP filter at all although I do appreciate that clear nights are at a premium right now.

 

[Somerled7]

1 hour ago, steppenwolf said:

I think that your CLS filter is perhaps giving you more problems than it is solving and the strong blue hue is overpowering the red making it hard to recover the signal. In my own quick processing run, the noise developed very quickly indeed.

It would be very interesting to see the results obtained from using no LP filter at all although I do appreciate that clear nights are at a premium right now.

 

OK Steve, thanks for looking into it.  It's early days for me and I am still getting together the gear that I need.  The CLS is the only filter I have at the moment, but maybe it's too strong and I should see what I can do without it.  Eventually I plan to get a dedicated Astro camera , but I'm not quite there yet.  

[steppenwolf]

11 hours ago, Somerled7 said:

Eventually I plan to get a dedicated Astro camera , but I'm not quite there yet.  

This will certainly make a big difference to your imaging. Is your light pollution predominantly Sodium or LED based? If it is Sodium based then an IDAS P2 LPS or IDAS D1 LPS filter would be a better choice as they don't impart any unwanted colour like the CLS does - I use an earlier version with my astro-CCD camera and have been very pleased with the results. The IDAS D2 LPS filter claims to be successful with LED lighting but I haven't put it to the test to confirm. Unfortunately, these filters come at a price but the Sodium ones absolutely work very well!

[MartinFransson]

Looks like you have a good start anyway! I would have to agree with steppenwolf about the filter. I had a CLS-CCD clip in for my DSLR and I thought it only made things a lot worse.

The other thing you might try is to use more but shorter exposures since your uncooled camera builds up quite a lot of heat noise. I don´t mean like really short but maybe 2-minute subs instead of 5-minute ones. Especially for such a bright target. My experience is that when you hit about 80 subs it really starts to bring the noise down with DSLR images.