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Gain and Sub-exposure calculation spreadsheet for the ZWO ASI183 and 294

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#51 basskep

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Posted 04 October 2019 - 03:05 AM

basskep,

 

 

   The pedestal is added during Image Calibration in PixInsight. I have forgotten which software you use for image processing. Many astrophoto processing programs allow the addition of a pedestal during image calibration. Some may call it something slightly different. Ask about how to do it in the specific program you use.

 

   For PixInsight, it is added using the ImageCalibration Process. That process window is shown below. The red oval marks the entry box for adding a pedestal. It is specified in PI to be entered in DN or ADU. In your case, you would simply put 800 in that box when calibrating your images prior to stacking.

 

attachicon.gif PI_Pedestal.png

Adding a pedestal in PixInsight. The default value is 0 as shown here. Pedestals are limited to 1000 DN  or ADU.

 

 

John

Thank you John for the pedestal explanation :-)



#52 basskep

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Posted 11 October 2019 - 05:04 AM

Hi,

 

If you know your sky background (from light pollution maps or a hand held SQM), then you only need to enter values in the blue boxes for cells D6 to D21

 

Swamp factor of around 10 is considered "the norm". (There are many CN threads on this).

I am using a Transmission Efficiency of 0.7 with success.  This includes the QE of the camera, plus whatever light is lost via coatings, etc.

For the 294, leave cells D14 and D15 as 550 and 100, respectively, as this is a one-shot-color camera, so I assume no additional filters are used (except maybe a standard UV-IR cur filter, which has no effect).

If you are cooling to -10C (as most are) you can use 0.008 to 0.010 for the Dark Current in Cell D12.  You would have to do tests to get that more accurate, but not all that important.

 

The rest are self-explanatory.

 

And yes, the resulting sub-exp, to achieve a Swamp Factor of 10, is in minutes

 

Good luck!

 

Steve

Hi Steve,

 

Sorry for coming back again on this subject but i have 2 more questions for you please :-)

 

1- If i don't know my sky background and don't fill in the "INPUT" section but instead i fill in the "Input Data from an Image" section it seems that no results appear on the right section "ZWO ASI 294 Gain-sub-exposure". Is it normal ?

 

2- If i know my sky background and fill in the "Input" section. Under D14 and D15 how could i do if i use a LP filter like the Optolong L eNhance which has several wavelengths (Ha, OIII, Hbeta) ? 

 

Thank you



#53 jdupton

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Posted 11 October 2019 - 02:43 PM

basskep,

 

   Hopefully, Steve will follow up on your questions. I will take a stab at it in the meantime. I am using Steve's "Revision K" of the spreadsheet.

  • Question 1: no results in sub-exposure table:
    I am not sure what might cause this. As long as I have not deleted any data from the blue input boxes of the "Input:" section, I get data populated in the table. Check to make sure you haven't accidentally deleted any data cells in the Input section. You may need to download the spreadsheet again if something was inadvertently changed.
     
  • Question 2: How to model the Optolong L-eNhance filter:
    This will depend on your imaging system. In essence, you will need to enter the "Effective QE" of the whole system in Cell D17. You should leave Cell D14 at 550 nm. I enter 150 nm in Cell D15 since I have a modeling spreadsheet that goes from 400 nm to 700 nm.

    I could give you a number to plug into Cell D17 if you wish to disclose which model telescope you image with. Also, I would need to know if you use any focal reducers and / or field flatteners. I would need the exact brand and model of each to model them in my spreadsheet.

    My spreadsheet has data for the sensor as well as a few selected filters of interest. (Currently the L-eNhance, Triad, Triad Ultra, AD Ha, AD Oiii, and IDAS LPS-P2 are included.)

    Once I know the details of the telescope and extra optics you use and filter of interest, I can give you the Effective QE of the complete imaging train to plug into Cell D17. The output sub-exposure table in Steve's spreadsheet will then give you reasonably accurate readings for use with your optics and filter combination.

   At some point, I can publish my optical train modeling spreadsheet but it's not ready for public consumption just yet.

 

 

John


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#54 niccoc1603

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Posted 11 October 2019 - 04:23 PM

The L-eNhance has a total 34nm bandwidth, so you can use these settings:
Wavelenght 550
Bandwidth 34

Edited by niccoc1603, 11 October 2019 - 04:23 PM.

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#55 basskep

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Posted Yesterday, 09:01 AM

basskep,

 

   Hopefully, Steve will follow up on your questions. I will take a stab at it in the meantime. I am using Steve's "Revision K" of the spreadsheet.

  • Question 1: no results in sub-exposure table:
    I am not sure what might cause this. As long as I have not deleted any data from the blue input boxes of the "Input:" section, I get data populated in the table. Check to make sure you haven't accidentally deleted any data cells in the Input section. You may need to download the spreadsheet again if something was inadvertently changed.
     
  • Question 2: How to model the Optolong L-eNhance filter:
    This will depend on your imaging system. In essence, you will need to enter the "Effective QE" of the whole system in Cell D17. You should leave Cell D14 at 550 nm. I enter 150 nm in Cell D15 since I have a modeling spreadsheet that goes from 400 nm to 700 nm.

    I could give you a number to plug into Cell D17 if you wish to disclose which model telescope you image with. Also, I would need to know if you use any focal reducers and / or field flatteners. I would need the exact brand and model of each to model them in my spreadsheet.

    My spreadsheet has data for the sensor as well as a few selected filters of interest. (Currently the L-eNhance, Triad, Triad Ultra, AD Ha, AD Oiii, and IDAS LPS-P2 are included.)

    Once I know the details of the telescope and extra optics you use and filter of interest, I can give you the Effective QE of the complete imaging train to plug into Cell D17. The output sub-exposure table in Steve's spreadsheet will then give you reasonably accurate readings for use with your optics and filter combination.

   At some point, I can publish my optical train modeling spreadsheet but it's not ready for public consumption just yet.

 

 

John

Hi John,

 

thanks for your reply.

Here is my setup :

- SC8 F/D10 

- SC8 F/D6,3 with Celestron FR

- ASI294MCPRO

- LP filter Optolong L-eNhance



#56 jdupton

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Posted Yesterday, 02:45 PM

basskep,

 

   OK, here are what I get for a Celestron C8 used with a Celestron F/6.3 Focal Reducer and an Opolong L-eNhance filter.

 

   I first looked at the optics. I could not find the optical design data for the focal reducer other than it has four elements. From other information I have seen, I think the focal reducer is organized as two groups of two element each. Plugging that information into my spreadsheet and assuming the scope is reasonably clean, I find the following:

 

basskep_Telescope.png

Calculation of Telescope Optical Transmission Properties.

 

   This result says that 81.4% of the light that enters the aperture of the scope is delivered to the next optical element, the focal reducer. After accounting for the central obstruction and light losses in the focal reducer, a total of 77.4% of the light that entered the telescope's aperture makes it to filter in front of the camera.

 

   Now we look at the camera's response to that light. Here is a plot of wavelengths showing the transmission through the filter and onto the sensor. (I have ignored the effects of light loss through the filter glass and the camera window + sensor cover glass.)

 

Sensor_Filter_Response.png

Net Effective Response Of Sensor With Filter.

 

   In this plot, the gray line is the response of the Opolong L-eNhance filter, the Red line is the response of the Red Bayer Pixels on the sensor, the Green line is the response of the Green Bayer Pixels on the sensor, and Blue line is the response of the Blue Bayer Pixels on the sensor. The dashed yellow line is the average response of a Bayer Quad (Red, Green, Green, Blue) of the sensor.

 

[Note that the spreadsheet graphs don't show very narrow values very well. Even though the Ha Peak of the filter looks too pointy, it is actually 5 nm wide in the data which is what gets integrated. Until I find a better way to plot the data, the graphs should be taken as approximations only.]

 

   If we integrate the area under the yellow curve, we get the average percentage of light that is captured by the sensor / filter combination over the wavelength range of 400 nm to 700 nm.

 

   That Total Effective Response is 4.07%. Now if we multiply by the Effective Throughput of the telescope, we get a result of 3.15%. This represents the percentage of photons that are actually captured per unit of time from the 8" aperture of your system.

 

   Now we can enter this into Steve's spreadsheet. Use the following inputs:

  • In Cell D17, enter 0.0315 -- This is the effective system QE of your full imaging train.
  • In Cell D15, enter 150 -- This is the (half)bandwidth over which the System QE was calculated.

   These should get you a result that is pretty close to real world. I have verified Steve's spreadsheet with real world results using this method. When I use a similar Effective System QE value for my own imaging setup and input data from a set of real images into the "Input Data from an Image" section, I get accurate Sky Brightness values that match my actual Unihedron SQM-L readings to within 0.1 mpass.

 

 

John


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#57 basskep

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Posted Today, 03:55 AM

basskep,

 

   OK, here are what I get for a Celestron C8 used with a Celestron F/6.3 Focal Reducer and an Opolong L-eNhance filter.

 

   I first looked at the optics. I could not find the optical design data for the focal reducer other than it has four elements. From other information I have seen, I think the focal reducer is organized as two groups of two element each. Plugging that information into my spreadsheet and assuming the scope is reasonably clean, I find the following:

 

attachicon.gif basskep_Telescope.png

Calculation of Telescope Optical Transmission Properties.

 

   This result says that 81.4% of the light that enters the aperture of the scope is delivered to the next optical element, the focal reducer. After accounting for the central obstruction and light losses in the focal reducer, a total of 77.4% of the light that entered the telescope's aperture makes it to filter in front of the camera.

 

   Now we look at the camera's response to that light. Here is a plot of wavelengths showing the transmission through the filter and onto the sensor. (I have ignored the effects of light loss through the filter glass and the camera window + sensor cover glass.)

 

attachicon.gif Sensor_Filter_Response.png

Net Effective Response Of Sensor With Filter.

 

   In this plot, the gray line is the response of the Opolong L-eNhance filter, the Red line is the response of the Red Bayer Pixels on the sensor, the Green line is the response of the Green Bayer Pixels on the sensor, and Blue line is the response of the Blue Bayer Pixels on the sensor. The dashed yellow line is the average response of a Bayer Quad (Red, Green, Green, Blue) of the sensor.

 

[Note that the spreadsheet graphs don't show very narrow values very well. Even though the Ha Peak of the filter looks too pointy, it is actually 5 nm wide in the data which is what gets integrated. Until I find a better way to plot the data, the graphs should be taken as approximations only.]

 

   If we integrate the area under the yellow curve, we get the average percentage of light that is captured by the sensor / filter combination over the wavelength range of 400 nm to 700 nm.

 

   That Total Effective Response is 4.07%. Now if we multiply by the Effective Throughput of the telescope, we get a result of 3.15%. This represents the percentage of photons that are actually captured per unit of time from the 8" aperture of your system.

 

   Now we can enter this into Steve's spreadsheet. Use the following inputs:

  • In Cell D17, enter 0.0315 -- This is the effective system QE of your full imaging train.
  • In Cell D15, enter 150 -- This is the (half)bandwidth over which the System QE was calculated.

   These should get you a result that is pretty close to real world. I have verified Steve's spreadsheet with real world results using this method. When I use a similar Effective System QE value for my own imaging setup and input data from a set of real images into the "Input Data from an Image" section, I get accurate Sky Brightness values that match my actual Unihedron SQM-L readings to within 0.1 mpass.

 

 

John

Thank you John,

 

Impressive !

And what about cell D14 (filter wavelength) ? Because the otptolong L-eNhance filter is a dual narrowband. We cannot fill in 2 values in D14...

I'm sorry but I really don't understand how this excel spreadsheet works because when I put some datas into the "Input Data from an Image" section then I have no results.

You can take a look at my excel file here : 

https://drive.google...E9sksquZNja4hqV



#58 jdupton

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Posted Today, 07:47 AM

basskep,

 

   Leave Cell D14 at the default value of 550 nm.

 

   That is the center wavelength of the pass-band that is assumed. With D14 at 550 nm and D15 at 150 nm, we are looking at all wavelengths between 400 nm and 700 nm. It is over that wavelength band that the "Average Effective System QE" is being calculated. That calculated average system QE is then entered in Cell D17.

 

 

John


Edited by jdupton, Today, 07:49 AM.


#59 basskep

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Posted Today, 07:56 AM

Thank you John for your response. Ok for cells D14 and D15 values but what about the "Input Data from an Image" section if I don't know my sky background in mag/sq-arcsec ?

If you look at the excel file I posted here :

https://drive.google...E9sksquZNja4hqV 

If I use data from an image it doesn't work ... 



#60 jdupton

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Posted Today, 08:12 AM

basskep,

 

   Enter the value of Cell H34 into Cell D6.

 

   You can either link the two as they were in the original spreadsheet or just type "20.26" into Cell D6. If you want to link them back as the original spreadsheet had them, enter "=H34" into Cell D6.

 

 

John


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#61 basskep

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Posted Today, 11:02 AM

basskep,

 

   Enter the value of Cell H34 into Cell D6.

 

   You can either link the two as they were in the original spreadsheet or just type "20.26" into Cell D6. If you want to link them back as the original spreadsheet had them, enter "=H34" into Cell D6.

 

 

John

The value of cell H34 gives me 20,37 ! It should be great to have a sqm at 20,37 under my suburb sky but honestly I don't think that it is the real value...


Edited by basskep, Today, 11:15 AM.


#62 jdupton

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Posted Today, 03:36 PM

basskep,

 

   I was only going by the screen shot you posted previously. It showed Cell H34 at "20.26". Also, the wavelength setting in your screenshot showed 656 nm when it should be set to 550 nm. If other areas of your copy of the spreadsheet have been changed, it might be a good idea to download the original again and start from a fresh copy.

 

 

John



#63 jdupton

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Posted Today, 04:02 PM

Steve, Nik, basskep, & others,

 

   This is sort of off topic but is related to Steve's spreadsheet(s). I have built a helper spreadsheet by extracting the information from my own "super-spreadsheet" containing imaging stuff. It was from this subset that I provided basskep with the information shown in Post #56 above. I now have those calculations in an easy to use standalone spreadsheet.

 

   This helper spreadsheet calculates the actual "Averaged System-Wide Effective QE" of your imaging system. It can be used to calculate the input value to be plugged into Steve's spreadsheet at Cell D17. It is also useful to play with to see how published "Peak QE" numbers stack up in the real world once all other factors are taken into account.

 

   The spreadsheet excerpt is still in beta stage. There may be errors but I am not finding any new bugs. Please report bugs to me. The spreadsheet in uploaded in "Open Desktop Foundation Spreadsheet" format. It is created in LibreOffice Calc but should open and operate correctly in most / all spreadsheet programs. Let me know if it doesn't.

 

   The spreadsheet can be expanded if you need me to add additional system parameters. The calculations currently support the following sensors, filters, Telescopes, and focal reducers / flatteners:

  • Sensors: Supported:
    No_Sensor
    Sony_IMX294_OSC
    Sony_IMX071_OSC
    Sony_IMX183_Mono
    Sony_IMX183_OSC
    Sony_IMX249_Mono
    Sony_IMX249_OSC
    Sony_ICX694_Mono
    Sony_ICX694_OSC
  • Filters Supported:
    No_Filter
    IDAS_LPS_P2
    L-eNhance
    OPT_Triad
    OPT_Triad_Ultra
    AstroDon_Ha
    AstroDon_Oiii
    AstroDon_eL
    AstroDon_eR
    AstroDon_eG
    AstroDon_eB
    AstroDon_eRGB
    AstroDon_iL
    AstroDon_iR
    AstroDon_iG
    AstroDon_iB
    AstroDon_iRGB
  • Telescopes Supported:
    Other (Fill In Your Own Specs)
    EdgeHD_11
    C8
    Ref_102_F7
  • Focal Reducers Supported:
    None
    EdgeHD_F/7
    Celestron_F/6.3

   This list is only for things I have used or thought might be useful. Additional sensors, filters, telescope systems, and focal reducers can be added on request. All I need is a link to manufacturers specification sheet and / QE plots.

 

   Once I get some feedback, I will make additions and post it under a new thread rather than (somewhat) burying it here. 

 

   You can download a copy from:

https://www.dropbox....gng-YJOo5a?dl=0

 

 

John


Edited by jdupton, Today, 05:16 PM.



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