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[Solved] Creating Master files queries  

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(@raed)
Molecular Cloud Customer
Joined: 9 months ago
Posts: 5
December 8, 2020 07:16  

Hello,

Can you please guide me to best practices when for my queries below:

  1. When shooting with dual band filters, do the darks, flats and biases need to be taken with the filter as well?
  2. When creating master files and BPM, does the debayer have to be set as per the filter used? (e.g. RGGB, Ha-OIII color, force CFA)
  3. Different nights, means different calibration files.  Do i keep each night separate or can i create master files by integrating all the different master flats, darks and biases as i acquire them?

Thanks

Raed

 


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(@volkanovun)
Main Sequence Star Customer
Joined: 12 months ago
Posts: 43
December 8, 2020 08:11  

@raed

For sure people, more experienced than me are going to answer and they will correct if I mention any wrong information.

1- Darks no need to be taken with any filter, but flats and biasses. Filters "filter" specific kind of lights and since darks have to be taken covering the scope there is zero light to be passed or cut, so no sense to use filter in dark frames. On the other hand, every filter have a specific spectrum and affect in different ways so flats and biasses need to be taken with filters.

 

2- BPM is a map of defected pixels, not related to filters. Defect pixels can not be "repaired" by using any filter.

 

3- You do not need to take darks, flats, biasses every night. You can use darks and BPM 1-2 yeras, then reneweng them is a good idea. But flats are different subject. You need to take flats every time when you change any optical condition eg.:

    a) When you change filterwheel (different brand different size etc. filterwheel)

    b) When you change scope

    c) When you change flattener/corrector

Otherwise you can use your masters.

 

Regards,

Volkan


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(@annehouw)
Main Sequence Star Customer
Joined: 4 years ago
Posts: 43
December 8, 2020 09:57  

What @volkanovun says. With one remark. You take bias as darks, just with a very short integration time. No need to do that per filter. And you can use bias for a long time, just as your darks and BPM.

So, the only calibration files to be done with filters are the flats. A flat with a NB filter will differ from a flat with a UV/IR filter. First of all because of the fact that there is different dust etc, but also because the transmission of a NB filter differs from centre to the edge because of the angle of the light and the bandpass shift in NB filters as a function of the angle. This is of particular interest with a fast system. For simplicity: if you change anything in your optical path, take new flats. And even when nothing changed...there might be new dust. So, it is a good habit to take flats every imaging session.


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(@raed)
Molecular Cloud Customer
Joined: 9 months ago
Posts: 5
December 8, 2020 10:09  

Thanks for the replies.  Much has been gained.  Just one more thing when it comes to calibrating the master flats (now I know it doesn't matter for the darks and biases 🙂 ), do the settings in tab 0 have to reflect the algorithm to use based on filter? Or this would only make sense once processing the lights?

I guess it is obvious to say the one should not stack flats of different sessions and filters.  

Thanks for the help.  Much appreciated.


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(@annehouw)
Main Sequence Star Customer
Joined: 4 years ago
Posts: 43
December 8, 2020 10:21  

Forgot about that:

Calibration works on the raw (non debayered) level. So it does not matter what you choose as debayer algorithm. Masters will be non-debayered.

This post was modified 6 months ago by Annehouw

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(@wvreeven)
Galaxy Admin
Joined: 3 years ago
Posts: 839
December 8, 2020 11:07  

Adding to the excellent advice given by @volkanovun and @annehouw, you also need to take new bias and darks if you change the ISO/gain, the temperature of the sensor or both. If you are using a cooled camera then you can reuse the bias and darks by always shooting at the same temperature (for instance -5° or -10°) and gain (for instance unity gain or a gain of 100 for modern ASI cameras). If you use a DSLR then it is much more complicated since those cameras almost never have active cooling (unless you modified it yourself).

 

Wouter


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(@raed)
Molecular Cloud Customer
Joined: 9 months ago
Posts: 5
December 8, 2020 14:28  

Thanks everyone for your inputs.  enjoying APP greatly so far, even more so this hobby despite the frustration 🙂


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