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Old 13-09-2021, 04:34 PM
Startrek (Martin)
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Calibration Frames and ZWOASI2600MC

I’ve never had to use darks , flats and other calibration frames at my dark site ( Bortle 3 ) on the South Coast as vignetting and gradients ( minimal ) are easily handled by my processing software Startools ( with or without NB filter and regardless of exposure lengths ) as this camera has almost zero amp glow and almost negligible dark current at -10C.
However since returning back to Bortle 8 Sydney skies ( with neighbours backyard and side flood lights on all night ) recently after being away for nearly 4 months , the Vignetting , dust donuts and gradients are a real problem when imaging targets like galaxies and globs etc... without a filter ( the 2600MC has a UV/ IR protective window , so in effect a Lum filter ) Even using the L Extreme filter requires additional work in processing to minimise these issues but no where near as bad as without a filter.
So now I’m going to have to take Flats to help mitigate these issues , something I’ve never had to do before. Also I believe the Skyglow in Sydney is getting worse year by year which is so evident.
Question: In regard to my 2600MC should I be taking Flats and Dark Flats to Calibrate in DSS or just Flats only.
In addition,I’ve read in a few forums that Bias frames are not usually required in CMOS cameras like the 2600MC , they are more useful in the older CCD type cameras

Any advice on the above would be very much appreciated

Thanks
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Old 13-09-2021, 06:11 PM
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Retrograde (Pete)
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Hi Martin,

When I first tried flats with the 2600mc (with dark-flats) I found my flats were badly over-correcting.
The solution (which I found on the internet: cloudynights.com/topic/731949-zwo-asi2600mc-pro-flats-cause-issues/page-2) was to use flats & bias frames & this seems to work well for me (so far at least).

I don't bother with darks.
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Old 13-09-2021, 06:23 PM
AdamJL
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I've been using Darks, Flats and Flat Darks.

Definitely keen to see what the consensus is here!
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Old 13-09-2021, 08:57 PM
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Flats calibrated with a good master bias is what I have found to work best with my ASI2600MC, and with the MM. Which is very handy as it means you do not need to shoot fixed length flats.

Lights I calibrate with the good master flat produced by that method, and either the master bias, or a master dark of the right gain, offset, exposure time and temp. On very long exposures I have found that without a good master dark (Which contains the bias info in my case) the master flat tends to overcorrect the corners as it amplifies what little dark current there is and brightens the corners.
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Old 14-09-2021, 07:43 AM
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kosborn (Kevin)
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I used to take flats, darks and bias with my asi1600mm. With the 2600mc I take flats, darks and flat darks. The subs seem to calibrate well and I now also use that combination for the 1600mm.
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Old 14-09-2021, 07:46 AM
Startrek (Martin)
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Quote:
Originally Posted by Retrograde View Post
Hi Martin,

When I first tried flats with the 2600mc (with dark-flats) I found my flats were badly over-correcting.
The solution (which I found on the internet: cloudynights.com/topic/731949-zwo-asi2600mc-pro-flats-cause-issues/page-2) was to use flats & bias frames & this seems to work well for me (so far at least).

I don't bother with darks.
Thanks Pete,
What capture software do you use ?
Sky flats with a white t shirt or LED flat panel with or without t shirt ?
We’re your flats exposure time calculated by the software and a quick check of the histogram ? or you selected around 30,000ADU like most forum posts suggested for this camera and ended up with an exposure time of between 2 and 3 seconds
Cheers
Martin
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Old 14-09-2021, 07:49 AM
Startrek (Martin)
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Quote:
Originally Posted by AdamJL View Post
I've been using Darks, Flats and Flat Darks.

Definitely keen to see what the consensus is here!
Thanks Adam,
How many flats do you take , exposure time and what capture software ?
Cheers
Martin
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  #8  
Old 14-09-2021, 07:53 AM
Startrek (Martin)
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Quote:
Originally Posted by The_bluester View Post
Flats calibrated with a good master bias is what I have found to work best with my ASI2600MC, and with the MM. Which is very handy as it means you do not need to shoot fixed length flats.

Lights I calibrate with the good master flat produced by that method, and either the master bias, or a master dark of the right gain, offset, exposure time and temp. On very long exposures I have found that without a good master dark (Which contains the bias info in my case) the master flat tends to overcorrect the corners as it amplifies what little dark current there is and brightens the corners.
Thanks Paul,
Capture software ?
Method of capturing Flats, no of Flats , ADU and exposure time ?
How many Bias frames to create master Bias
Thanks
Martin
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Old 14-09-2021, 07:59 AM
Startrek (Martin)
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Quote:
Originally Posted by kosborn View Post
I used to take flats, darks and bias with my asi1600mm. With the 2600mc I take flats, darks and flat darks. The subs seem to calibrate well and I now also use that combination for the 1600mm.
Thanks Kevin,
Sorry to pick everyone’s brains and I know that each optical system is different but trying to gather enough data on the 2600MC so I’m not waisting to much time outside capturing and determining the most suitable calibration methods
Capture software ?
Method obtaining your Flats ( white t shirt or not ? ) no of Flats , exposure times and ADU count ?
Thanks
Martin
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Old 14-09-2021, 09:54 AM
AdamJL
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Quote:
Originally Posted by Startrek View Post
Thanks Adam,
How many flats do you take , exposure time and what capture software ?
Cheers
Martin
Hi Martin

40 Flats, 40 Dark flats, 40 Darks
Exposure time is calculated by NINA, depending on the light source. I set NINA to target a histogram mean of 32768 (50%) with a 10% tolerance.
Minimum exposure is usually 2 seconds, maximum is 20 seconds.

For light source, I use either
- a Huon tracing panel, with pieces of white paper between the panel and the scope to dim it a little (even on the dimmest setting, it's usually too bright)
- wait for morning, then slew to zenith, use the sky brightness and pieces of white paper again

I've had the issue of corners overcorrecting though, as mentioned above by Paul. This was a while ago but it seems to be okay these days.

Thanks for starting this topic. I took 100 bias each last night at various gain settings and -10 temperature (temperature probably doesn't make any difference but I did it anyway).
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Old 14-09-2021, 11:44 AM
Startrek (Martin)
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Quote:
Originally Posted by AdamJL View Post
Hi Martin

40 Flats, 40 Dark flats, 40 Darks
Exposure time is calculated by NINA, depending on the light source. I set NINA to target a histogram mean of 32768 (50%) with a 10% tolerance.
Minimum exposure is usually 2 seconds, maximum is 20 seconds.

For light source, I use either
- a Huon tracing panel, with pieces of white paper between the panel and the scope to dim it a little (even on the dimmest setting, it's usually too bright)
- wait for morning, then slew to zenith, use the sky brightness and pieces of white paper again

I've had the issue of corners overcorrecting though, as mentioned above by Paul. This was a while ago but it seems to be okay these days.

Thanks for starting this topic. I took 100 bias each last night at various gain settings and -10 temperature (temperature probably doesn't make any difference but I did it anyway).
Thanks Adam
Calibration is not talked about that often on the forum, only when folk need some advice like me , I’ve managed without it for some time but it’s bitten me on the bum now and I have to learn and use it especially in Sydney
Cheers
Martin
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Old 14-09-2021, 02:05 PM
Startrek (Martin)
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I’m probably reading to much about Calibration and not imaging and experimenting ( inclement weather for the next 5 days ) but in regard to Flats

I’ve read that in regard to the latest ZWO CMOS cameras -
1/ If your Flats are between 1.5 and 3 seconds you only require to take and add Dark Flats for Calibration
2/ If your Flats are under 1.0 second you only require to take and add Bias frames for Calibration

Comments welcome
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Old 14-09-2021, 02:23 PM
AdamJL
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and what happens if you're over 3 seconds?

I'm usually anywhere from 7-14 seconds.
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Old 14-09-2021, 03:21 PM
Startrek (Martin)
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Originally Posted by AdamJL View Post
and what happens if you're over 3 seconds?

I'm usually anywhere from 7-14 seconds.

.......and your flats eliminate vignetting and dust motes ? then most of the stuff I’ve read and seen throws that info out the window
Thanks
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Old 14-09-2021, 05:59 PM
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Retrograde (Pete)
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Quote:
Originally Posted by Startrek View Post
Thanks Pete,
What capture software do you use ?
Sky flats with a white t shirt or LED flat panel with or without t shirt ?
We’re your flats exposure time calculated by the software and a quick check of the histogram ? or you selected around 30,000ADU like most forum posts suggested for this camera and ended up with an exposure time of between 2 and 3 seconds
Cheers
Martin
Hi Martin,
I'm currently just using Sharpcap (but plan to transition to NINA)

I use the white T-shirt & flat panel method & go for the correct exposure/histogram.
Exposure lengths are probably shorter than ideal though.

Pete
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Old 14-09-2021, 06:05 PM
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Quote:
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.......and your flats eliminate vignetting and dust motes ? then most of the stuff I’ve read and seen throws that info out the window
Thanks
I don't have the 2600, but do have a 533 (so same sensor tech), and I find flats when using a dual-band filter are usually like 8s or so targetting 20,000 ADU. They are much (much) shorter when using a UV/IR cut.

However, even from Sydney I don't ever find I need flats on such a small sensor.
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Old 14-09-2021, 06:18 PM
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A few posts since I last posted so I wont quote individual posts, just lay out my answers.

Firstly, I am using Voyager for capture. I aim for at least 25 flats. With my refractor I set an approx 30K ADU target with a 10% tolerance and have Voyager shoot dawn sky flats for me. It starts with a 15 second default exposure and works it out for itself from there with shrinking exposure times as the sky brightens, and big dithers between flats so any stars captured calibrate out.

I would not worry about any split of method for calibrating the flats with the ASI2600. I have had good results calibrating with just a master bias everywhere from around 30 second exposures when I had an NB filter in the image train, to well under 1 second when I have started shooting flats a bit late and the sky is getting bright.

With my newt I am using a light panel (Controlled by Voyager) and shooting flats at night as I need to chase down a light leak that makes sky flats patchy, it is either sneaking around the main mirror cell or around the focuser drawtube. Voyager starts at a default exposure time and default panel brightness and varies both as required to hit the target ADU.

Last edited by The_bluester; 15-09-2021 at 06:07 AM.
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Old 14-09-2021, 07:25 PM
Startrek (Martin)
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Quote:
Originally Posted by Retrograde View Post
Hi Martin,
I'm currently just using Sharpcap (but plan to transition to NINA)

I use the white T-shirt & flat panel method & go for the correct exposure/histogram.
Exposure lengths are probably shorter than ideal though.

Pete
Thanks Pete
I’ll be using a white t shirt and my Huion A3 dimmable light panel to take flats
I only image with solid tube newts so I’ll also use a shower cap spray painted black and fitted over the back end to stop light leakage or entry
Cheers
Martin
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Old 14-09-2021, 07:40 PM
Startrek (Martin)
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Originally Posted by Craig_ View Post
I don't have the 2600, but do have a 533 (so same sensor tech), and I find flats when using a dual-band filter are usually like 8s or so targetting 20,000 ADU. They are much (much) shorter when using a UV/IR cut.

However, even from Sydney I don't ever find I need flats on such a small sensor.
Thanks Craig,
Great information
I use the Optolong L Extreme duel band to image emission Nebula and the 2600MC has a UV/ IR protective window so I can expect longer exposures using this arrangement.
Your 533MC has a 14bit ADU ie: max ADU of 32,768 so applying 50% would be around 16,400 ADU. Choosing higher at 20,000 ADU at the same illumination level would take a longer exposure , right ??
Cheers
Martin
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Old 14-09-2021, 07:47 PM
Startrek (Martin)
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Quote:
Originally Posted by The_bluester View Post
A few posts since I last posted so I wont quote individual posts, just lay out my answers.

Firstly, I am using Voyager for capture. I aim for at least 25 flats. With my refractor I set an approx 30K ADU target with a 10% tolerance and have Voyager shoot dawn sky flats for me. It starts with a 15 second default exposure and works it out for itself from there with shrinking exposure times as the sky brightens, and big ditehrs between flats so any stars captured calibrate out.

I would not worry about any split of method for calibrating the flats with the ASI2600. I have had good results calibrating with just a master bias everywhere from around 30 second exposures when I had an NB filter in the image train, to well under 1 second when I have started shooting flats a bit late and the sky is getting bright.

With my newt I am using a light panel (Controlled by Voyager) and shooting flats at night as I need to chase down a light leak that makes sky flats patchy, it is either sneaking around the main mirror cell or around the focuser drawtube. Voyager starts at a default exposure time and default panel brightness and varies both as required to hit the target ADU.
Paul
Thanks for your details
I only use solid tube newts , and now have a Huion A3 dimmable light panel to take my flats
I’ll make sure my newt is sealed at the base ( blackened shower cap )
All the information provided by everyone to date is fantastic
The weekend is suppose to be fine so I’ll be out capturing and testing
Cheers
Martin
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