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Gain and Sub-Exposure Calculator Spreadsheet for ZWO Cameras

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#1 StevenBellavia

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Posted 29 January 2021 - 04:31 PM

Hi,

 

I added a new feature to the Gain and Sub-Exposure Calculator Spreadsheets for ZWO Cameras.

 

You can now choose a filter and it will auto-populate the wavelength and bandpass.

 

This is what is available in the drop-down list, but I can add more:

 

LUM
Red
Green
Blue
Ha 12 nm
Ha 7nm
Ha 6nm
Ha 3 nm
OIII 12 nm
OIII 7nm
OIII 6nm
OIII 3 nm
SII 12 nm
SII 7nm
SII 6nm
SII 3 nm
Optolong L-Enhance
ZWO Duo
Triad
IDAS Duo

 

So far the spreadsheet is available for the following ZWO cameras:

071, 183, 294, 533, 1600, 2600 and 6200

 

The link to download a copy of the spreadsheet for your use (no edit permission):

 

https://drive.google...8VJ?usp=sharing

 

Note that if you have a One-Shot-Color (OSC) version of any of these cameras, pick the Green Filter.

 

I am currently working on several QHY cameras.  I will let you know when those are complete.  They too will have this new filter drop-down list feature.

 

Same notes as before, but posting here again:

 

Notes:

1. Much of the theory and equations came from Jon Rista, Frank, Craig Stark, and others (Thank you!)

2. I recommend to only use the main (first) sheet. Blue boxes are for user entry, everything else is calculated for you.  If you don't want to use image data to calculate the sky background and camera dark current, just enter those values directly to the best of your ability, but it will remove the calculation.  Instructions how to restore it or on the spreadsheet.

3. The "Transmission Efficiency" of the entire optical system is likely the largest potential source of error.  Play with it until your data matches a hand-held SQM, or known sky brightness value. I find 0.5 to 0.7 works for me.

4. The common thinking is you want a Swamp Factor of around 10.  However, with narrow-band, especially at darker sites, this becomes impracticable.

5. I arbitrarily fixed the "object signal" to 22.0 magnitude/square arc-second.  This is to compare imaging an object from two different sites, with different sky brightness, so as to have an apples-to-apples comparison.  If you actually know your object's brightness, change the "22" in that equation to the desired value. This will only affect SNR calculations.

5. It is just a guide.  No precision was intended. The camera specifications were obtained by eyeballing the graphs that ZWO posts on their website, or from users who submitted data using SharpCap, etc.  Feel free to contact me with better data, if you have it.

7. Offset (Bias) values seem to vary, and the values I have chosen are just a guide. ZWO often divides by 5 for some reason. i.e., multiply the ZWO offset by 5 to get the camera ADU's (But not always).

8. These spreadsheets are not all that different form the Gain and Sub-exposure tables posted on other CN threads and should have similar results as running SharpCap's Smart Histogram, live in the field.

Special thanks to Nik Coli, and John Upton, who have been running these spreadsheets on their 183, 294 and 1600, and finding and fixing all my errors.

 

 

Steve

Attached Thumbnails

  • Sample_Spreadsheet.jpg

Edited by StevenBellavia, 30 January 2021 - 09:09 AM.

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#2 niccoc1603

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Posted 12 February 2021 - 09:29 AM

Fantastic Steve

The spreadsheet is my holy grail for subs exposure!

#3 StevenBellavia

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Posted 17 March 2021 - 07:24 AM

I've added one more filter, the IDAS LP D1.

 

The spreadsheets are for the following ZWO ASI cameras:

071, 183, 294, 533, 1600, 2600, 6200

And the following QHY cameras:

168, 183, 367, 600

And the Omegon 1600

 

This is a list of all the filters currently available, in alphabetical order:

 

Blue
Green
Ha 12 nm
Ha 3 nm
Ha 6 nm
Ha 7 nm
IDAS Duo
IDAS LPS D1
Lum
OIII 12 nm
OIII 3 nm
OIII 6 nm
OIII 7 nm
Optolong L-Enhance
Red
SII 12 nm
SII 3 nm
SII 6 nm
SII 7 nm
Triad
ZWO Duo


Edited by StevenBellavia, 17 March 2021 - 07:31 AM.

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#4 dcaponeii

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Posted 17 March 2021 - 07:39 AM

Any chance you can add the Orion Starshoot range of cameras?  G10, G16, G26, etc.  Or if I match the sensor to one of the equivalent ZWO cameras will I get correct values? (I suspect not because the Gain values for the camera software don't match the equivalent ASI values.)



#5 StevenBellavia

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Posted 23 March 2021 - 07:58 AM

If the Gain call-outs are different, it will not work.

 

I will take a look.

 

While waiting, have you tried SharpCap's Smart Histogram?  I've been told that yields nearly identical results:

 

http://docs.sharpcap...rtHistogram.htm


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#6 Greg F

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Posted 23 March 2021 - 09:01 AM

I've added one more filter, the IDAS LP D1.

 

The spreadsheets are for the following ZWO ASI cameras:

071, 183, 294, 533, 1600, 2600, 6200

And the following QHY cameras:

168, 183, 367, 600

And the Omegon 1600

 

This is a list of all the filters currently available, in alphabetical order:

 

Blue
Green
Ha 12 nm
Ha 3 nm
Ha 6 nm
Ha 7 nm
IDAS Duo
IDAS LPS D1
Lum
OIII 12 nm
OIII 3 nm
OIII 6 nm
OIII 7 nm
Optolong L-Enhance
Red
SII 12 nm
SII 3 nm
SII 6 nm
SII 7 nm
Triad
ZWO Duo

Thank you for the great work.

 

Can you provide a link for the QHY cameras, the link at the beginning of this thread only lists ZWO cameras.

 

Thank you

 

Greg



#7 AhBok

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Posted 23 March 2021 - 09:12 AM

. . . While waiting, have you tried SharpCap's Smart Histogram?  I've been told that yields nearly identical results:

 

http://docs.sharpcap...rtHistogram.htm

Thanks for all your contributions to astrophotography Steve! I use Smart Histogram and it tracks with your spreadsheet beautifully. Your spreadsheet is more convenient, especially for planning.



#8 StevenBellavia

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Posted 23 March 2021 - 09:47 AM

Gain-Sub-exposure Spreadsheets for QHY cameras:

 

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

 

The QHY 600 Mode 1 is now complete.  Looks like Gain 56 is the magical gain to use for most instances.


Edited by StevenBellavia, 23 March 2021 - 11:20 AM.


#9 dx_ron

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Posted 23 March 2021 - 10:32 AM

From a new owner of a new-to-me QHY183C - Thanks! This is awesome.

 

For OSC, are the recommended subexposure times (using the Green filter) interpreted as-is, or do they require an OSC fudge factor?

 

And one filter request - the Optolong L-Extreme is quite popular with OSC owners (no rush on my end, as I don't own one yet).


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#10 StevenBellavia

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Posted 23 March 2021 - 11:21 AM

From a new owner of a new-to-me QHY183C - Thanks! This is awesome.

 

For OSC, are the recommended subexposure times (using the Green filter) interpreted as-is, or do they require an OSC fudge factor?

 

And one filter request - the Optolong L-Extreme is quite popular with OSC owners (no rush on my end, as I don't own one yet).

Yes, use Green, as-is.  That is as close as you can get with an OSC camera.

 

I will try to add the Optolong L-Extreme soon.

 

(:


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#11 Astro_kev

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Posted 02 April 2021 - 05:03 PM

I'm also new Owner of a ASI 071 MC PRO. It's my first CMOS. 

I try to find Infos about the Offset setting, but without success. That is all New 4 me. 

 

Then I found this spreadsheets. But the Offset sheet for my cam are not complete...

I've read that the minimum pixel value of a Dark Frame has to be about 100, is this correct? When I take a Dark with gain 50 and offset 20 the minimum value are only 4. I think it's to low, because no signal is detected from this pixel. 

(300s, -15c). If I use an offset around 55 the min value is about 100.

 

CS

Kevin


Edited by Astro_kev, 02 April 2021 - 05:27 PM.

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#12 philinbris

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Posted 02 April 2021 - 06:07 PM

Yes, use Green, as-is.  That is as close as you can get with an OSC camera.

 

I will try to add the Optolong L-Extreme soon.

 

(:

+1 on the L-eXtreme.

This is fantastic work Steve.

Cheers



#13 StevenBellavia

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Posted 03 April 2021 - 10:05 AM

I'm also new Owner of a ASI 071 MC PRO. It's my first CMOS. 

I try to find Infos about the Offset setting, but without success. That is all New 4 me. 

 

Then I found this spreadsheets. But the Offset sheet for my cam are not complete...

I've read that the minimum pixel value of a Dark Frame has to be about 100, is this correct? When I take a Dark with gain 50 and offset 20 the minimum value are only 4. I think it's to low, because no signal is detected from this pixel. 

(300s, -15c). If I use an offset around 55 the min value is about 100.

 

CS

Kevin

When you say the min value around 100, is that in 16 bit, that is on a scale of 0 to 65,535?

If so, yes, 100 is too low for a bias frame.  I like to shoot for around 500.

 

Also realize that too much offset is not the end of the world.  You may lose a tiny bit of dynamic range, but that camera has plenty.  But clipping the dark end is disastrous.  That is the part of the signal you are trying to get.

 

This is a good read regarding offset, though perhaps old, it is still valid:

 

http://www.stark-lab...inAndOffset.php



#14 StevenBellavia

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Posted 03 April 2021 - 10:45 AM

+1 on the L-eXtreme.

This is fantastic work Steve.

Cheers

I have added the Optolong L-extreme filter to all the ZWO, QHY and Omegon spreadsheets.

 

I have not done Orion cameras yet, as I do not know where to find the camera data. If you have it from the manufacturer or from a good SharpCap Sensor Analysis, I will take it.

 

Steve


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#15 Astro_kev

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Posted 03 April 2021 - 11:08 AM

Thanks for your reply.
The min value of 100 I read in Another Text...
I'm pretty confused about this Thing.
How can I find out what the optimal offset is for a gain value?

And Thanks for the Link. I will Look at it. :)

CS and happy Eastern

Edited by Astro_kev, 03 April 2021 - 11:10 AM.

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#16 AstroFrankMontana

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Posted 03 April 2021 - 11:37 AM

This is a wonderful bit of work! Thanks!


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#17 DavidCloudy

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Posted 04 April 2021 - 05:51 AM

I've added one more filter, the IDAS LP D1.

 

The spreadsheets are for the following ZWO ASI cameras:

071, 183, 294, 533, 1600, 2600, 6200

And the following QHY cameras:

168, 183, 367, 600

 

I think QHY183M's offset are a little bit off in the spreadsheat.

183 has way lower offset than other qhy cameras, you can see in their FAQ

 

gain 11, offset 8 produces around 500 ADU (16bit) bias median



#18 StevenBellavia

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Posted 04 April 2021 - 09:00 AM

I think QHY183M's offset are a little bit off in the spreadsheat.

183 has way lower offset than other qhy cameras, you can see in their FAQ

 

gain 11, offset 8 produces around 500 ADU (16bit) bias median

Thank you for that information.  (I was not far off with a Gain of 9.8)

 

I have updated the QHY 183 spreadsheet, which now has the following Offsets, using an Offset of 8 for Gain 11 as the basis of the estimate for the other Gains.

 

Gain Offset
 0          2
11         8
15       13
20       21
30       61
40     202

 

This should provide approximately 600 16-bit ADU's for BIAS frames, but please check and report back if you can.

 

Steve


Edited by StevenBellavia, 04 April 2021 - 09:20 AM.


#19 DavidCloudy

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Posted 04 April 2021 - 09:34 AM

Thank you for that information.  (I was not far off with a Gain of 9.8)

 

I have updated the QHY 183 spreadsheet, which now has the following Offsets, using an Offset of 8 for Gain 11 as the basis of the estimate for the other Gains.

 

Gain Offset
 0          2
11         8
15       13
20       21
30       61
40     202

 

This should provide approximately 600 16-bit ADU's for BIAS frames, but please check and report back if you can.

 

Steve

Thank you!

I get a little lower 16bit ADU (exactly 512) with 11/8 for the bias, but its not zero clipped, so seems fine!

(because of the black level calibration, i get the most dark around 0.5sec, which is 464 16bit ADU and it is still not clipped!)


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#20 DavidCloudy

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Posted 29 September 2021 - 03:47 AM

@StevenBellavia are you sure about the filter bandwidth values for OSC cameras?

 

Lets take a example with Optolong L-extreme. It is a Duoband filter, 7nm around OIII and 7nm around Ha.

With mono cameras, it is correct, every pixel collects data in 14nm overall bandwidth, that is in the spreadsheet!

Meantime OSC cameras has the bayer filter on the sensor, which is another filter and block 'red' pixels to collect OIII data and 'green' and 'blue' pixels are blocked from Ha...

So every pixel collects photons in 7nm bandwidth (with different QE...) so i think, for the OSC cameras 14nm bandwidth is missleading


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#21 ChrisMoses

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Posted 01 October 2021 - 11:40 PM

Very cool!

Thx



#22 StevenBellavia

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Posted 03 October 2021 - 07:04 PM

@StevenBellavia are you sure about the filter bandwidth values for OSC cameras?

 

Lets take a example with Optolong L-extreme. It is a Duoband filter, 7nm around OIII and 7nm around Ha.

With mono cameras, it is correct, every pixel collects data in 14nm overall bandwidth, that is in the spreadsheet!

Meantime OSC cameras has the bayer filter on the sensor, which is another filter and block 'red' pixels to collect OIII data and 'green' and 'blue' pixels are blocked from Ha...

So every pixel collects photons in 7nm bandwidth (with different QE...) so i think, for the OSC cameras 14nm bandwidth is missleading

You are correct.  The filter values may not be 100% accurate for OSC Cameras.

I will need to make a correction to account for  narrowband and multi-band filters with an OSC camera.

I will work on that 

And you mention QE.  So far I have not included the QE for each camera, in regards to each color.  That might take a while to do.  I am starting with the ASI 2600MC, because that seems to be very popular.  I didn't realize it had such a low QE in the red (60% versus 90% for the blue, and 84% for green).


Edited by StevenBellavia, 03 October 2021 - 07:39 PM.


#23 StevenBellavia

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Posted 03 October 2021 - 08:15 PM

For the ZWO ASI 2600MC, using the L-Extreme, this is what I come up with for total bandpass:

 

  Blue: 1 of the 4 pixels allow the 7nm of OIII (500nm) light through at 0.90 QE

Green: 2 of the 4 pixels allow the 7nm of OIII (500nm) light through at 0.84 QE

   Red: 1 of the 4 pixels allow the 7nm of Ha  (656nm) light through at 0.60 QE

 

So the total bandpass becomes:

 

(7 x .25  x .90)  = 1.575
(7 x .50  x .84)  = 2.940
(7 x .25  x .60) =  1.050

Total Bandpass = 5.565 nm

 

So that is very different than 14nm. 

 

I ran it through the spreadsheet with the new values, and this is the comparison to achieve a Swamp of 2.0 in a 20.0 sky with an f/7 telescope::

 

For 14nm  Bandpass, recommended sub-exposure at Gain 100:  0.87 minutes

For 5.6nm Bandpass, recommended sub-exposure at Gain 100:  2.25 minutes

 

So that is a significant difference.

 

I have to do this for all the narrowband and multi-band  filters on all OSC cameras. 

 

It is going to take quite a while to get through all of them, but I will try.

 

Thanks for pointing it out.

 

Steve



#24 StevenBellavia

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Posted 06 October 2021 - 06:51 AM

Hi again,

There are currently (as of today) two versions of the ASI 2600 spreadsheet.

The one that has "Beta" in the name is a work-in-progress, and I strongly suggest using the non-Beta version.

The Beta takes into account the sensor absolute and relative QE and the losses through the CFA Bayer matrix just for the OSC version of the 2600.

It may be too harsh, and I suspect the final version will end up someplace in the middle of the two spreadsheets.

For both versions, if using no filter or a luminance filter, choose "LUM OSC" in the filter pulldown.

For the Beta version, I have the duo, tri and quad-band filters end with "OSC".

 

As always, if you have real data, adjust the Transmissions Efficiency (Cell D17) until the reported sky background (Cell D6) matches a handheld SQM or the known sky brightness for your area.

 

Special thanks to John Upton who provided volumes of insight and data.

 

Steve


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