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Is this Normal? MONO Camera

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#1 venyix

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Posted 21 September 2020 - 08:38 PM

So, I'm switching from a DSLR workflow to a mono workflow. I have recently purchased a ZWO 183, and I'm finding the processing curve fairly steep. Obviously the major bummer with mono is taking three times as long, but I'm okay with that so long as the results are worth the extra time, but so far my results have been kind of disappointing. My first target with this camera was the Cygnus Loop, but I'm seeing quite a bit of noise in my 5 minute subs. Here are some examples.

 

This is a single 5 minute sub with 300 gain (camera default) and 10 black level set in APT. I stacked this single image with one dark sub to remove the amp glow.

https://drive.google...iew?usp=sharing

This is zoomed in on the same image

https://drive.google...iew?usp=sharing

 

This is a stacked image with 24 exposures 5 minute subs

https://drive.google...iew?usp=sharing

Zoomed in

https://drive.google...iew?usp=sharing

 

This is the full stacked image with moderate stretching...

https://drive.google...iew?usp=sharing

 

 

After some research I have noticed that 300 gain is probably not the best to use, and I'm assuming that the "black level" setting in APT in supposed to correspond with the offset...

 

Here are my questions:

 

1) Is this level of background noise expected?

2) After capturing 8 hours of data across 3 different narrowband filters at gain 300 offset 8, should I dump the data and re-shoot with a lower gain?

3) Is there a setting in DSS that I'm not using properly when stacking these images?

4) If I stack 50 subs instead of 25, will this reduce that noise in the slightest?

 

Here is what I'm using....

 

Explore Scientific 80mm Triplet

ZWO ASI183 MONO

Optolong Ha, SII, OIII Filters

Apertura 60mm Guide Scope

Orion Starshoot G3 DSO (re-purposed as guide camera)

Sky-Watcher EQ6-R Pro

 

Astrophotography Tool

Photoshop

PixInsight (Just started using it)

DeepSkyStacker

Sequator (Unfortunately doesn't seem to handle the .fit files that the 183 produces, so I haven't been using it since the switch)

 

Edit:

   I am NOT binning...


Edited by venyix, 21 September 2020 - 08:40 PM.


#2 venyix

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Posted 22 September 2020 - 09:17 AM

Bump, any other mono users?



#3 RJF-Astro

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Posted 22 September 2020 - 10:23 AM

Hi Venyix, a great switch but not always one that happens by itself. It has a big impact on workflow and processing.

 

I do not really understand your initial statement. Mono does not take 3 times as long. Only the part with flats takes longer, and you have some extra steps to take in calibration and post processing. But from a data collection point of view, mono is just as fast or faster than OSC (it depends on if you use L and how you stack and proces).

 

Your questions:

 

1. Yes it looks normal. When I compare it to a single sub of the Veil I made last month it looks comparable. That was a 10 minute sub with the ASI1600, 3nm filter and lens at f/5.6. I set the gain to 175. A 3 hour image brought out very nice detail in the Ha shell of the Cygnus loop.

2. I would proces the data and use the next clear nights for a new target. Part of the learning curve. Or redo it if you really like that target.

3. Hard to tell. What stacking method do you use? Kappa sigma clipping is the recommended setting. You could also dive into PixInsight stacking and calibration. Read Warren Kellers book for this, available as e-book.

4. 50 should improve SNR over 25. Not as drastically as lower numbers, but it should be visible. Watch out when comparing with STF though, see below.

 

Do be aware that the ScreenTransferFuntion in PixInsight really makes all nasty things visible. If you use STF and just started using PixInsight with you mono cam, this can put you off. I had this experience. But when I looked at my older dslr images in PixInsight with STF, they looked much worse. Just go ahead and proces the mono images like you would normally and judge them by the end result. I am sure they will be fine, the 183MM is a geat camera.



#4 venyix

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Posted 22 September 2020 - 10:35 AM

Hi Venyix, a great switch but not always one that happens by itself. It has a big impact on workflow and processing.

 

<...snip...>

My reasoning behind 3x as long is related ti the SHO palette and capturing the channels separately instead of all at once. I’m trying to learn more about PixInsight as it seems very powerful for AP. I’ll process this data and see how it goes, thanks for the reply!



#5 RJF-Astro

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Posted 22 September 2020 - 11:21 AM

Ok, let us know how it works out!

 

And by the way for SHO, mono is faster compared to capturing narrowband with and OSC. You could use a duo or multiband filter to speed up in OSC. But the fact is that quantum efficiency will drop. A red h-alpha photon will be blocked by 75% of the filters in the bayer pattern. Mono does not have this drop in QE, and so the signal to noise ratio in the stacked image will be higher. There are techniques to compensate for this difference, but the fact that with mono you collect signal per filter does not make it slower.



#6 Navige

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Posted 22 September 2020 - 11:34 AM

I recently switched to mono from DSLR. I have the Altair Hypercam 183M pro which uses the same sensor as your camera. I ran the sensor analysis in sharp cap and it shows me where unity gain is for my camera, 389. Then if you run the histogram tool and then click the brain it will tell you what the best exposure time is for each filter based on your background sky. I knew this was a very sensitive sensor but I was amazed that only 8s is the recommended expose for my L filter at unity gain and around 25s for RGB filters. I have not yet run this with my narrowband filters but I expect the recommended exposure time to be around 120s.

The only processing issue that I have run into is narrowband with the wrong temperature darks. I thought 10 degrees wouldn’t matter but it does. The amp glow starburst won’t be removed without the matching temperature darks.

#7 klaussius

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Posted 22 September 2020 - 02:16 PM

2) After capturing 8 hours of data across 3 different narrowband filters at gain 300 offset 8, should I dump the data and re-shoot with a lower gain?
I don't think that's necessary (dumping already captured data).
 
You can stack both sessions and then merge them together as is normal with multi-session projects. As long as the sessions are properly weighed according to their total integration time, there should be no need to dump perfectly good data.
 
That's assuming you don't find any other fault with the data that would warrant dumping it.


#8 venyix

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Posted 22 September 2020 - 11:46 PM

Ok, let us know how it works out!

 

And by the way for SHO, mono is faster compared to capturing narrowband with and OSC. You could use a duo or multiband filter to speed up in OSC. But the fact is that quantum efficiency will drop. A red h-alpha photon will be blocked by 75% of the filters in the bayer pattern. Mono does not have this drop in QE, and so the signal to noise ratio in the stacked image will be higher. There are techniques to compensate for this difference, but the fact that with mono you collect signal per filter does not make it slower.

This is my first attempt, I tried the hubble palette, but I think I should not go with it for this nebula.

Veil Nebula (Version 1)



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