Combining-stacking fit files from different nights

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TSquasar avatar
Does stacking two or three fit files, which were acquired using ASILive on different nights, generally produce the same result as one long session and one fit file?

For example, if two fit files from different nights, with one having ASILive stacking 1000 subs and another fit file having come from 1500 stacked subs, if these two are then stacked does the resulting fit file have essentially the same result as one single session with ASILive stacking 2500 subs?

(Assuming viewing conditions and setup were all the same on both nights)
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André Bremer avatar
The right way to combine data it is to calibrate subs with their respective calibration frames from each night (bias, dark, flats, etc…smile, then register and stack all calibrated subs together across all nights.
TSquasar avatar
Thanks Andre' for the quick response!

Assuming that all the calibrations were done and one now has a stacked fit file for a given night.
Can that fit file be combined with other fit files from other nights and  get the same result as one long session?
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André Bremer avatar
Theoretically yes… but you’ll get a better result if you integrate the calibrated subs (per filter of course), rather than complete per-night stacks. Weighting and pixel rejection will work a lot better if all subs are considered for final integration.
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TSquasar avatar
Thanks again Andre'!!
andrea tasselli avatar
It depends on how you weigh the exposures, if you do or the software you're using does.
Torben van Hees avatar
It is not a matter of weighting but of normalising the subframes. PixInsight will do this correctly with standard parameters, or using the WBPP script or with NormalizeScaleGradient.
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andrea tasselli avatar
Torben van Hees:
It is not a matter of weighting but of normalising the subframes. PixInsight will do this correctly with standard parameters, or using the WBPP script or with NormalizeScaleGradient.


It is a matter of what software you are using. It is fallacious to assume that the OP has or uses PI. Besides, it is a matter of weighting as a measure of the quality of the frames (SNR and FWHM).
Torben van Hees avatar
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Much more in-depth: Astrophotography Manual https://www.amazon.de/Astrophotography-Manual-Practical-Scientific-Approach/dp/1138055360
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at my level, it is better that I properly prepare the basic settings of the photos

Actually, you can probably just stack them with the others in most software. It's important you have full calibration files, though (flats, darks, flat-darks or bias).
Bob Lockwood avatar
In my experience, and this is from friends that have added files from years of doing the same object to be added to the original. Once the Fits files have been calibrated and saved, it doesn’t matter when they were taken. The software doesn’t look at the dates taken, just the files them self. Add as many calibrated fits sub frame as you want.
Torben van Hees avatar
Torben van Hees:
Actually, you can probably just stack them with the others in most software. It's important you have full calibration files, though (flats, darks, flat-darks or bias).


Thanks you for the Books. For all my samples I have calibration files exepted flat-darks. I have an APN, flat-darks are they important ?

Sorry, what is an APN? For most cameras you can use bias instead of flat-darks.
Torben van Hees avatar
You will probably be fine with bias only.