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Author Topic: using lights and flats from several imaging session  (Read 845 times)

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Offline squreshi786

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using lights and flats from several imaging session
« on: 14:31:45, 26 December, 2016 »
Hello

I usually get lights,darks and bias on the same night of imaging and without altering the optical path or focus get the flats the next day or the day after usually. And then I calibrate in PI all this data. Then I take off my camera and separate my scope and store every thing away.
I repeat the same on the next imaging session.
I would like to use my lights and calibration frames from several nights but when i COMBINE THE DATA THE PI Crashes. Its likely that PI does not want to me combine data during which the optical path has been modified (the major issue is that the orientation of the camera would have changed more than anything.)

Would anyone know a way around this, i.e. get PI to accept lights and calibration frames over several nights accepting that camera orientation might have been changed. Is there any alternative?

Secondly how precisely does the camera orientation needs to be that PI could be cheated and it would accept the frames over several nights when things have been dismantled and re-setup.
Losmandy G11, Gemini-1, GEMINI-ASCOM, Pole Master QHY, Takahashi TSA-102 F/8, Altair astro 60mm Guide scope (piggybacked). Loadstar X2 autoguider. PHD2 Autoguiding. Canon 600 T3 (Astronomiser modified). Pixinsight Processing

Offline Nimbus

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Re: using lights and flats from several imaging session
« Reply #1 on: 15:17:21, 26 December, 2016 »
While you can combine images from many different nights quite easily, you cannot use the original flats if you disturb the optical path as it would be all be impossible to get everything aligned perfectly.

I am not a PI user so advice on that will have to fall to someone else, but PI cannot do it if you disturb the optical train either.

If you can leave the camera attached then you can use a set of flats over a period of time by refocusing only for different sessions. But do NOT alter the orientation of the camera.

HTH Jim
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Offline chris.bailey

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Re: using lights and flats from several imaging session
« Reply #2 on: 17:20:26, 26 December, 2016 »
Sorry but PI has no knowledge of the camera orientation. I combine data from different nights and even different cameras, scopes, orientation, flipped and mirrored all the time and PI takes it in its stride.

Jim is right through that a nights images SHOULD be calibrated with that nights flats (Darks and Bias don't need to be taken each time).

There is some suggestion that the release of PI made just before Xmas introduced a bug but I have seen nothing further on this, understandably. Its working fine for me.

Chris
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Offline darkstar3d

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Re: using lights and flats from several imaging session
« Reply #3 on: 18:56:28, 26 December, 2016 »
Did PI run out of memory or hard drive space perhaps? It can get slow if you are low on memory and have lots of data. It actually warned me about hard drive space. Which is why I bought terabytes a few weeks ago.


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Offline squreshi786

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Re: using lights and flats from several imaging session
« Reply #4 on: 17:08:56, 27 December, 2016 »
Thanks for this Chris
But you don't suppose sharing with me how exactly you do this. i.e. combine lights and flats from several sessions. I use batch preprocessing script. Presumably you are suggesting that if I have 50 lights and 20 flats from 1 night and same from 2nd night irrespective of change in camera orientation, I should load all lights and all flats in the script and it should work?

Saqib
Losmandy G11, Gemini-1, GEMINI-ASCOM, Pole Master QHY, Takahashi TSA-102 F/8, Altair astro 60mm Guide scope (piggybacked). Loadstar X2 autoguider. PHD2 Autoguiding. Canon 600 T3 (Astronomiser modified). Pixinsight Processing

Offline chris.bailey

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Re: using lights and flats from several imaging session
« Reply #5 on: 17:42:05, 27 December, 2016 »
Saqib

I don't use the batch pre-processing script. To be honest I find it takes as long to load all the files into the right places as it does to do it long hand. So doing it my long hand way.

1) Load all the lights from a session into ImageCalibration with the relevant flats, darks and bias. Repeat for each session. You now have a set of calibrated light frames suffixed _c

2) If you are not dithering the light frames I would recommend running CosmeticCorrection with Autocorrect hot and cold with a cold sigma of around 4 and a hot sigma of around 3.

3) Load ALL of the calibrated light frames into Star Alignment and use one that has the target nicely framed as the reference. ONLY IF you are using different scope combinations pick a 2-d spline Registration Model and turn on Distortion Correction. You now have a set of registered frames suffixed _c_r (_c_cc_r if you use cosmetic correction)

4) Integrate the registered frames using whatever flavour of pixel rejection you prefer. If you have 100 frames then Windsor or Linear Fit.

Give it a go. Doing it long hand soon becomes second nature and you can tweak settings at each step.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

 

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