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Advancing in Imaging Skills

Astrophotography Beginner CMOS DSO Filters
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#1 xmj0001

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Posted 03 March 2021 - 08:20 PM

OK, so I've got the back focus of my Orion Starshoot G21 figured out with my EON 110 refactor.  In addition I've been successful in a quick and accurate polar alignment with the pole-master (Best astronomy tool product ever!!) and my hyper-tuned CGX-L is now spot on when slewing to DSO after a multi-star alignment and calibration.  I do the normal two star setup then add 4 more for good measure.  Now the new problems

 

I seem to have what seem to be dust spots in all my images  - I believe the solution for this is to take flat frames after each imaging session, problem is i don't know exactly what would be a good flat frame?  I know the temp doesn't matter, the image train needs to be the same focus and all, and i need a even white light source which I'm getting a dimmable led panel.  How do i calculate the ADU or what light luminescence/color settings should i have on the panel, in general i have researched this and all i can find is the histogram should be 2/3rds to the right.

 

Next I'm in Bortle 6/7 skies and i believe a light pollution filter might help on my current targets M81/M82, M42, M51,M101 and M13.  I have an old Broadfilter i had from ten years ago in my visual C6R days, it is a Thousand Oaks Optical Broadband Filter LP-1B 2inch, would this be any good i know filter tech has greatly advanced i've been suggested to buy either a Optolong or Astronomik

 

Any thoughts



#2 Ken Sturrock

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Posted 03 March 2021 - 08:37 PM

Congratulations on figuring out the back focus!

 

1.) It's going to depend on your software as to how you measure the brightness of your flat frame subs. You can go by the histogram approach, you can also go for a median (or mean) value as well. You can also make some judgement based on a stretch of the frame. Does it seem to show the light fall-off, dust motes and other optical issues? For example, here's a picture of one of my flat frames in The SkyX:

 

Screen Shot 2021-03-03 at 18.32.38.png

 

2.) Check out a thread which was posted last night in this very forum.



#3 CoHPhasor

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Posted 04 March 2021 - 03:06 AM

Even if you dont use NINA for your sequencing program, I'd advise it for flats.

You have to configure the software to know your image train, but then the flat wizard helps do the rest.
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#4 xmj0001

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Posted 04 March 2021 - 11:33 AM

Thanks for the suggestions

 

1.  I'm going to look into NINA and other software to see if there are tools to help create good flats

2.  I'm going to increase target exposure time more frames not just longer frames say compare 3hrs of 1min (180 frames) v 3hrs of 2min (90 frames) and use the TOO LP-1 to see if it makes a difference if not i wont use it.



#5 dswtan

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Posted 04 March 2021 - 11:52 AM

1.  I'm going to look into NINA and other software to see if there are tools to help create good flats

Totally endorse NINA for this (and so much more), but you'll find a "flats wizard" or similar function in various imaging/sequencing programs, e.g. Sharpcap has this, SGP, Voyager, APT, etc. It won't be a standalone tool, just to be clear. Sorry if obvious.
 



#6 Ken Sturrock

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Posted 04 March 2021 - 12:48 PM

I, too, would advocate for using a tool to help automate flats because they are finicky and can be laborious if you have a lot of filters or regularly change your camera/OTA relationship.

 

Like all types of automation, though, I'd still urge you to continue to figure it out manually first so that you're comfortable with the process before turning things over to the sorcerer's apprentice.


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#7 xmj0001

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Posted 05 March 2021 - 10:19 AM

thanks everyone for the help

I believe I'm getting better, I'm still trying to understand and figure out the flat frame settings and process.

I dont understand ADU basically i took the flat frames using a LED light panel at 50% with a white T-Shirt over the telescope lens for  5 sec

 

I'm reading thru the NINA and SharpCAP documentation but it is intense

 

I posting two images here one with the flat frames and the other before flat frames.  I believe i can see a slight improvement

 

Before

M81_1
 
After (with flat frame removal)
M81_2

 

 

I've got lots to learn like framing my image the same all the time, also tonight I'm going to up the Gain 50% to 15 but reduce the time by 50% to min, increase the frames to 120.  I think more shorter frames will be better for the G21 camera


Edited by xmj0001, 05 March 2021 - 10:21 AM.


#8 Ken Sturrock

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Posted 05 March 2021 - 10:43 AM

Looks like you're making some progress.

 

Although controversial, because flats also compensate for brightness differences among pixels, many people advocate that your flats be shot at the same gain as your lights. In your case, though, that's probably not your current issue. Remember, also, that your flat frames will need to be dark calibrated like any other light frame. There have been two recent threads (in both BDSI & EDSI) during the past week that you might want to look through.

 

If you're new to flat frames, you might find this tutorial from the Astro Imaging Channel to be useful. It's all background, but it was presented by Peter Kalajian who created the Flat Man (& Flip Flat). If you can read faster than the typical YouTube video, he authored a similar article, here.

 

Keep at it. You'll figure it out and soon you'll be helping others!



#9 xmj0001

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Posted 06 March 2021 - 11:54 AM

Good News and Bad News

Getting better with flats - Good News

Images last night too faint (not enough stars) for DSS - Bad News (4hrs in the cold wasted)

 

Also getting better with photoshop - here is my image of M101 from a couple of nights ago

M101 20210304 0305

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