Determining "best" ADU level for ASI1600MM Pro Mono Flats

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STEVE333 United States of America
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#21

Post by STEVE333 »


SPOILER ALERT!!!

The "Flats problem" I've been dealing with turns out to have been caused by a bad Master Bias frame!!!!
It had nothing to do with the mean ADU value of the flats. I was "chasing my tail"! How embarrassing.

Since starting with the ASI1600MM I have been working at a Gain of 140 (working with LRGB filters) and have been using the same Master Bias (I believe it was also taken at a Gain of 140). For some reason the Master Bias frame had what looked like "amp glow" around the edges. Since the Bias frame is subtracted from each Light frame during calibration it caused each calibrated Light frame to be too dark around the edges which I misinterpreted as bad Flats correction.

For the last couple of days I've switched the Gain to 200 to work with Sii, Ha, Oiii filters. When I created the new Bias frame (at a Gain of 200) I noticed it had uniform brightness from edge to edge (unlike the Bias frame created at Gain 140). When I applied it to Light frames taken at Gain 200 the result was nearly perfect Flats correction!! I was, needless to say, overjoyed!!! I've been fighting this problem for a few months now, and, was getting rather frustrated.

Now I just need to find out why the Bias frames taken at Gain 140 were bad. I've heard others say that Bias frames for the ASI1600MM are a problem. I'm taking the Bias frames at an exposure of 0.0001 sec (100 microseconds) which is longer than the stated shortest exposure time of 60 microseconds.

Sorry for any confusion I've caused.

Cheers,

Steve
Steve King: Light Pollution (Bortle 5)
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#22

Post by Graeme1858 »


That's interesting. That's a bit of a result sorting out your bias frame problem. Hope you can find out what was causing it.

Regards

Graeme
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#23

Post by Baskevo »


[mention]STEVE333[/mention] I have heard a lot of people have issues with bias frames for the ASI1600mm, which is why I never even tried them. I am sure you have read this, but you can take dark flats to replace the bias frames, which works well.

I am glad you have figured it out!
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#24

Post by STEVE333 »


Baskevo wrote: Sun May 10, 2020 10:46 am [mention]STEVE333[/mention] I have heard a lot of people have issues with bias frames for the ASI1600mm, which is why I never even tried them. I am sure you have read this, but you can take dark flats to replace the bias frames, which works well.

I am glad you have figured it out!
Thanks - I will definitely be checking my Bias frames from now on! The funny thing is that I tried Dark Flats at one point, but, they didn't help. My Dark Flats exposures are only about 1 sec for the SHO filters and only a few tenths for the LRGB filters which doesn't seem that much different from the 0.0001 sec for the Bias frames. Oh well, at least I now know what to look for.
Graeme1858 wrote: Sun May 10, 2020 5:43 am That's interesting. That's a bit of a result sorting out your bias frame problem. Hope you can find out what was causing it.

Regards

Graeme
Thanks Graeme - I'm very excited to have solved this problem. While everybody else was "running ahead" with their beautiful NB images I was "stumbling and tripping at the starting line". Now I'm excited to join the race. Can't wait for Nebula season to start.

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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#25

Post by UlteriorModem »


Many say that bias frames are not even necessary for a cmos camera. If you do use a master bias, and or master darks, do not calibrate them. Just stack them with no correction. (all weights = 0).

I think a lot of folks overthink the adu value for the flats. There is no real magic bullet and more often than not they end up somewhere around 20-30k. Fact is if the flats 'look good' they probably are. The main thing is to not saturate them.

Often gradients will be in some images that have nothing to do with your imaging train. They come from sky conditions, moon glow, sky glow / light pollution, and high thin clouds, sometimes even space dust. Nothing can really be done about these other than careful background extraction in processing.

Flats main purpose is to try to eliminate dust doughnuts and not really gradients. Though they can help some with that.
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#26

Post by Graeme1858 »


UlteriorModem wrote: Sun May 10, 2020 3:28 pm Flats main purpose is to try to eliminate dust doughnuts and not really gradients. Though they can help some with that.

And vignetting?
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#27

Post by UlteriorModem »


Vigenetting / gradients, kind of the same thing :D
Tom

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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#28

Post by STEVE333 »


UlteriorModem wrote: Sun May 10, 2020 5:35 pm Vigenetting / gradients, kind of the same thing :D

There is actually a bit of a difference between vignetting and gradients.

Vignetting has to do with the variations in light transmission across your telescope/filter/camera FOV. It will be the same for every image taken through your system (assuming your system isn't disassembled or your camera rotated). Vignetting usually show up with the image being brighter in the center and darker as you go towards the edges of the image. This type of variation is corrected with Flats. Correction with Flats is performed during image calibrations.Flats also correct for dust motes on the camera sensor or on any filters near the camera.

Gradient refers to the variation in brightness of the image caused by some form of light pollution across the FOV. Even after correcting your images with Flats, gradients will still be present. Gradients are corrected during image processing (not during image calibrations like Flats).

Hope this makes sense.

Steve
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#29

Post by STEVE333 »


I finally found the full answer to my problems with creating Flats for my ASI1600MM Pro camera. This camera has a CMOS sensor, and, it isn't calibrated in the same way as my old DSLR or other CCD cameras. The answer was provided in a 9-Part tutorial by Adam Block (see link below).

https://www.youtube.com/playlist?list=P ... JGoJz7tlxF

My Flats now work as expected.

Steve
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#30

Post by XCalRocketMan »


The key to my issues (couldn't remove the amp glow) with the ASI1600 has been to eliminate the use of BIAS frames altogether. ZWO recommends this as well as a large community of CMOS users. I have started to either use dark flats or just regular flats. Once I eliminated the BIAS frames my amp glow issues disappeared.
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#31

Post by STEVE333 »


XCalRocketMan wrote: Fri May 29, 2020 2:54 am The key to my issues (couldn't remove the amp glow) with the ASI1600 has been to eliminate the use of BIAS frames altogether. ZWO recommends this as well as a large community of CMOS users. I have started to either use dark flats or just regular flats. Once I eliminated the BIAS frames my amp glow issues disappeared.
Glad to hear your amp glow problems are gone. I too no longer use Bias frames. I do use the Dark Flats when making my MasterFlat. For the Lights I only use the MasterDark and MasterFlat frames (again with no Bias frames used).

Can't wait to get to do my first real NB imaging in June.

Cheers - Steve
Steve King: Light Pollution (Bortle 5)
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Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#32

Post by XCalRocketMan »


STEVE333 wrote: Fri May 29, 2020 4:30 am
XCalRocketMan wrote: Fri May 29, 2020 2:54 am ...
Can't wait to get to do my first real NB imaging in June.

Cheers - Steve
NB opens a whole new world of imaging, especially in LP zones. Even the moon won't interfere until near full. Allows me to image on any clear night.
Scopes Celestron EdgeHD-11; William Optics GT102; William Optics ZS61; Criterion Dynamax-8 SCT
Mounts AP1100GTO mount w/APCCpro; iOptron iEQ30 Pro; Criterion Dynamax-8 SCT
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Guiding Celestron OAG w/ASI174mm mini; WO 50mm; Orion ST80
Cameras and Filters ZWO2600mm Pro w/Optolong 3nm NB and RGB; ZWOASI1600mm Pro (ZWO LRGB and Astrodon Ha-5nm, Oiii-3nm, Sii-5nm), QHY10, Canon 50D; ASI174mm mini; ASI462MC; ASI120MC
Misc Moonlite focuser on Edge - Feather-Touch focuser on GT102; ZWO EAF on ZS61; ZWO 2" and 31mm FWs; Kendrick Dew System, Temp-est Fans
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#33

Post by STEVE333 »


My approach to solving the Flats problem has been completely wrong!!!!

Because I'm using an ASI1600MM CMOS camera it turns out I can't use the same calibration approach I used for my DSLR camera. A great video tutorial series by Adam Block (link below) shows how to use the new PixInsight WBPP script. In the 9th (last) part he discusses the proper calibration approach to use for a CMOS camera. His approach worked perfectly, and, I am now able to create excellent Flats. In fact, I now use Flats with a mean value of about 32,000 ADU and they work perfectly.



As an aside, I now use the WBPP script to calibrate my images. I was always afraid to try the BPP script when I was calibrating my DSLR images. Now that I've switched to NB imaging I find the WBPP script to be a real time saver. It handles all of the image sorting, making of calibration masters (Flats and Darks), calibration of the RAW images and registration of the master NB images.

Hope this is helpful for some of you.

Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#34

Post by stargazer27 »


STEVE333 wrote: Mon Jun 01, 2020 10:28 pm My approach to solving the Flats problem has been completely wrong!!!!

Because I'm using an ASI1600MM CMOS camera it turns out I can't use the same calibration approach I used for my DSLR camera. A great video tutorial series by Adam Block (link below) shows how to use the new PixInsight WBPP script. In the 9th (last) part he discusses the proper calibration approach to use for a CMOS camera. His approach worked perfectly, and, I am now able to create excellent Flats. In fact, I now use Flats with a mean value of about 32,000 ADU and they work perfectly.



As an aside, I now use the WBPP script to calibrate my images. I was always afraid to try the BPP script when I was calibrating my DSLR images. Now that I've switched to NB imaging I find the WBPP script to be a real time saver. It handles all of the image sorting, making of calibration masters (Flats and Darks), calibration of the RAW images and registration of the master NB images.

Hope this is helpful for some of you.

Steve
Steve, this has been a great help for processing using the ASI1600MM Pro. I have always had correction issues with flats. I started out with a Nikon D5500, and never suffered through the amount of head scratching I've encountered with this cooled astrocam. I've invested in a Spike-a-flat panel, countless hours devising tinting solutions for it due to dimmer banding problems, invested in a Starizona LF corrector for my 12" SCT to lessen coma and vignetting to avoid flat corrections, and spent countless hours doing/undoing processing steps in Pixinsight. I actually found this thread and watched this video some time ago, but totally missed the point for some reason.

I do have one question for you. You said you had success with this calibration process. My frames no longer appear over-corrected due to the lack of bias subtraction, but I have noticed an extreme increase in noise in the final integrated product. I'm unsure if the noise was always present but was being overcorrected out, or the bias was indeed doing the noise reduction. Since we do not optimize the dark frames, which generally would remove some of the noise as it is part of the optimization process, is it just a process of using noise reductions techniques now? I'm basically curious if you noticed an increase in final integration noise when not subtracting bias or optimizing dark frames.

Thanks!
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#35

Post by STEVE333 »


stargazer27 wrote: Sat Feb 06, 2021 8:55 pm Steve, this has been a great help for processing using the ASI1600MM Pro. I have always had correction issues with flats. I started out with a Nikon D5500, and never suffered through the amount of head scratching I've encountered with this cooled astrocam. I've invested in a Spike-a-flat panel, countless hours devising tinting solutions for it due to dimmer banding problems, invested in a Starizona LF corrector for my 12" SCT to lessen coma and vignetting to avoid flat corrections, and spent countless hours doing/undoing processing steps in Pixinsight. I actually found this thread and watched this video some time ago, but totally missed the point for some reason.

I do have one question for you. You said you had success with this calibration process. My frames no longer appear over-corrected due to the lack of bias subtraction, but I have noticed an extreme increase in noise in the final integrated product. I'm unsure if the noise was always present but was being overcorrected out, or the bias was indeed doing the noise reduction. Since we do not optimize the dark frames, which generally would remove some of the noise as it is part of the optimization process, is it just a process of using noise reductions techniques now? I'm basically curious if you noticed an increase in final integration noise when not subtracting bias or optimizing dark frames.

Thanks!

You mention that the Dark Frames are not optimized:
  • The Dark Frames contain the same offset information that the Bias frames do. So, when the Master Dark frame is used in calibration it removes the same fixed offsets that the Master Bias normally removes. That is why no Master Bias is subtracted from either the Light or Dark frames.
  • Multiple Dark Frames are averaged together to reduce the noise in the resulting Master Dark Frame.
What I'm saying is that the Master Dark frame is "optimized".

To answer your question, I haven't had any unusual noise problems when using this approach.

Hope this helps. If not please let me know.

Cheers,

Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#36

Post by XCalRocketMan »


STEVE333 wrote: Mon Feb 08, 2021 6:33 am
stargazer27 wrote: Sat Feb 06, 2021 8:55 pm Steve, this has been a great help for processing using the ASI1600MM Pro. I have always had correction issues with flats. I started out with a Nikon D5500, and never suffered through the amount of head scratching I've encountered with this cooled astrocam. I've invested in a Spike-a-flat panel, countless hours devising tinting solutions for it due to dimmer banding problems, invested in a Starizona LF corrector for my 12" SCT to lessen coma and vignetting to avoid flat corrections, and spent countless hours doing/undoing processing steps in Pixinsight. I actually found this thread and watched this video some time ago, but totally missed the point for some reason.

I do have one question for you. You said you had success with this calibration process. My frames no longer appear over-corrected due to the lack of bias subtraction, but I have noticed an extreme increase in noise in the final integrated product. I'm unsure if the noise was always present but was being overcorrected out, or the bias was indeed doing the noise reduction. Since we do not optimize the dark frames, which generally would remove some of the noise as it is part of the optimization process, is it just a process of using noise reductions techniques now? I'm basically curious if you noticed an increase in final integration noise when not subtracting bias or optimizing dark frames.

Thanks!

You mention that the Dark Frames are not optimized:
  • The Dark Frames contain the same offset information that the Bias frames do. So, when the Master Dark frame is used in calibration it removes the same fixed offsets that the Master Bias normally removes. That is why no Master Bias is subtracted from either the Light or Dark frames.
  • Multiple Dark Frames are averaged together to reduce the noise in the resulting Master Dark Frame.
What I'm saying is that the Master Dark frame is "optimized".

To answer your question, I haven't had any unusual noise problems when using this approach.

Hope this helps. If not please let me know.

Cheers,

Steve
Are you using Dark Flats?
Scopes Celestron EdgeHD-11; William Optics GT102; William Optics ZS61; Criterion Dynamax-8 SCT
Mounts AP1100GTO mount w/APCCpro; iOptron iEQ30 Pro; Criterion Dynamax-8 SCT
Lenses Hyperstar-III; Celestron 0.7x FR; WO Flat/Reducer 0.8x
Guiding Celestron OAG w/ASI174mm mini; WO 50mm; Orion ST80
Cameras and Filters ZWO2600mm Pro w/Optolong 3nm NB and RGB; ZWOASI1600mm Pro (ZWO LRGB and Astrodon Ha-5nm, Oiii-3nm, Sii-5nm), QHY10, Canon 50D; ASI174mm mini; ASI462MC; ASI120MC
Misc Moonlite focuser on Edge - Feather-Touch focuser on GT102; ZWO EAF on ZS61; ZWO 2" and 31mm FWs; Kendrick Dew System, Temp-est Fans
Software NINA; PHD; APT; BYE; PI; APP; PSP; Registax; FireCapture; SharpCap
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Re: Determining "best" ADU level for ASI1600MM Pro Mono Flats

#37

Post by STEVE333 »


XCalRocketMan wrote: Tue Feb 09, 2021 1:06 am Are you using Dark Flats?

Yes, I use Dark Flats, but, only when calibrating the Flat frames.

1) Take Dark Flat frames of the exact same exposure as the Flat frames.
2) Average the Dark Flats to make a Master Dark Flat.
3) Subtract the Master Dark Flat from each Flat frame before averaging them to create the Master Flat

The Dark Flats are not used with the Light frames.

Cheers,

Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
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