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Multi-night procedure question

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#1 unimatrix0

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Posted 04 May 2021 - 03:13 PM

Ok, I got a question, may sound noob  and dumb. 
Assume you're working on one object on multiple nights. 
Do you take flats each night for that set of subs? 
If you do, and you process the image, how do you process that? 
Let's say you have 4 days of subs, each day has its own set of flats

Do you process each set with its flats  and then what?   

You got 4 images processed, correct? 

Do you stack those 4 images? 

I mean, I see some people sticking on the same object for months and they got like 20+hrs of exposure, that sounds like a nightmare to process, keeping things organized? 

Or do you have some way to process all and assign each set of flats to each set of nights of subs? 

I have no experience using Pixinsight am I guessing right it has the capability to combine multi sessions? 


Edited by unimatrix0, 04 May 2021 - 03:14 PM.


#2 Tapio

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Posted 04 May 2021 - 03:22 PM

DSS, APP can do multiple night stacking.
You can also just calibrate each nights lights and save them.
Then in the end you take all calibrated frames and align/stack them.
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#3 Dynan

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Posted 04 May 2021 - 03:35 PM

+1 for APP.

 

Keep a good library of master darks and biases, then add them for the entire calibration session. Then you only need to match each session's flats with the lights.

 

APP makes it a dream.

 

I 'Blink' and analyze my lights in PI for convenience, but you can pan through them any way you like.


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#4 pedxing

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Posted 04 May 2021 - 03:42 PM

Ok, I got a question, may sound noob  and dumb. 
Assume you're working on one object on multiple nights. 
Do you take flats each night for that set of subs? 
If you do, and you process the image, how do you process that? 
Let's say you have 4 days of subs, each day has its own set of flats

Do you process each set with its flats  and then what?   

You got 4 images processed, correct? 

Do you stack those 4 images? 

I mean, I see some people sticking on the same object for months and they got like 20+hrs of exposure, that sounds like a nightmare to process, keeping things organized? 

Or do you have some way to process all and assign each set of flats to each set of nights of subs? 

I have no experience using Pixinsight am I guessing right it has the capability to combine multi sessions? 

Yes, you take flats each night unless you have a permanent (observatory) setup. (some may argue that you don't necessarily have to do this, but it is the safest course of action)

You apply each night's flats (and your master dark) to the subs from that night.

You end up a set of calibrated subs for each night.

Normally you don't stack each night separately (unless you are curious and want to see how it stacks as you go along).

You register each set of calibrated subs to the same alignment sub (your choice which one you use) so that they are all lined up with each other.

Then you stack all of the aligned subs.

Yes, you need to keep your files organized, but once you get a system in place it's not too much of a burden.

Plate solving is your friend during acquisition.


Edited by pedxing, 04 May 2021 - 03:48 PM.


#5 jonnybravo0311

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Posted 04 May 2021 - 07:01 PM

You calibrate each night individually. You then take all of the nights' calibrated data and register and stack it together to produce a single image.


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#6 Alex McConahay

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Posted 04 May 2021 - 07:33 PM

In my observatory setup, I can go for some time (a couple of months) without gathering new flats or darks. So, I can batch calibrate with one operation. All the frames from the several months can use the same calibration run. 

 

With my traveling rig, I can go the whole weekend, or whole week long star party on the same basis. 

 

What these two situations have in common is that I am using the same exposures, same regulated temperatures, the same configuration, and I am not disassembling and reassembling the rig. It stays together the whole time. 

 

If, however, any of these conditions change, it is time to at least make new flats. And if exposure values change, new darks and so forth. 

 

Some pre processing programs can handle these "groups" for you. (A group being all the subs taken in any one configuration, usually in one night.) Others cannot. The important thing is that any given exposure is CALIBRATED with flats, darks, biases, etc. that match that particular evening. Flats change every time you change the imaging train (disassemble, assemble it). Darks and Biases not so much. But they can change when you change exposure values. 

 

Once the subs are calibrated (and cosmetically corrected), then the important thing is to take ONE frame (your best and sharpest) and align all the other frames, regardless of night, to that one sample frame. And stack from there.

 

Alex


Edited by Alex McConahay, 04 May 2021 - 07:47 PM.

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#7 unimatrix0

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Posted 05 May 2021 - 09:27 AM

In my observatory setup, I can go for some time (a couple of months) without gathering new flats or darks. So, I can batch calibrate with one operation. All the frames from the several months can use the same calibration run. 

 

With my traveling rig, I can go the whole weekend, or whole week long star party on the same basis. 

 

What these two situations have in common is that I am using the same exposures, same regulated temperatures, the same configuration, and I am not disassembling and reassembling the rig. It stays together the whole time. 

 

If, however, any of these conditions change, it is time to at least make new flats. And if exposure values change, new darks and so forth. 

 

Some pre processing programs can handle these "groups" for you. (A group being all the subs taken in any one configuration, usually in one night.) Others cannot. The important thing is that any given exposure is CALIBRATED with flats, darks, biases, etc. that match that particular evening. Flats change every time you change the imaging train (disassemble, assemble it). Darks and Biases not so much. But they can change when you change exposure values. 

 

Once the subs are calibrated (and cosmetically corrected), then the important thing is to take ONE frame (your best and sharpest) and align all the other frames, regardless of night, to that one sample frame. And stack from there.

 

Alex

Thanks! 
Great replies guys,  the last time I tried to multi-stack 4 different sets of imaging sessions, I think I made the process unnecessarily over-complicated for myself. 

I kept creating darks and biases and 4 nights of data of the same object  (Rosetta)  and as the final result, it looked like I was photographing a mud puddle  (lol). 
My problem was, that the offset was different in one sets (but I had the correct darks for it)  and I blame poorly taken flats (too short exposures, didn't take the dust or water drops out ), perhaps I should try stacking them again, but leave out the flats, to see just what I was supposed to get. 



#8 KTAZ

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Posted 05 May 2021 - 09:40 AM

Thanks! 
Great replies guys,  the last time I tried to multi-stack 4 different sets of imaging sessions, I think I made the process unnecessarily over-complicated for myself. 

I kept creating darks and biases and 4 nights of data of the same object  (Rosetta)  and as the final result, it looked like I was photographing a mud puddle  (lol). 
My problem was, that the offset was different in one sets (but I had the correct darks for it)  and I blame poorly taken flats (too short exposures, didn't take the dust or water drops out ), perhaps I should try stacking them again, but leave out the flats, to see just what I was supposed to get. 

So to recap;

 

1) Take new flats whenever you modify/rotate your imaging train or change exposure parameters

2) Calibrate each nights lights with the proper calibrated flats

3) Everything AFTER lights calibration can be done to all the calibrated lights in one batch (ie., cosmetic correction, debayer, registration, etc.)

 

One of the most important points made thus far is to be sure you use the SAME LIGHT as your reference image during Registration. Otherwise you will have problems.

 

EDIT: I saw where you asked about PI being able to combine multiple nights. As Alex noted, the WBPP script does that, but TBH you should do it manually until you truly understand what is involved and how the results look. It just provides for a better base of understanding and experience.


Edited by KTAZ, 05 May 2021 - 09:42 AM.


#9 Alex McConahay

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Posted 05 May 2021 - 10:24 AM

>>>>>1) Take new flats whenever you modify/rotate your imaging train or change exposure parameters

 

Unless I misunderstand, a change in the exposure parameters do not mean new flats are necessary. By that, I mean you can use the same flats on a 30 second exposure as on a 300 second exposure (as long as the imaging train did not change). And on a gain of 0 or a gain of 100. (Or ISO changes). The darks must change if you change those parameters, but they all use the same flats (as long as the imaging train is the same....and I suppose as long as the dust has not moved!!!).

 

  

>>>>>>I saw where you asked about PI being able to combine multiple nights. As Alex noted, the WBPP script does that,

Just to clarify, I think WBPP will do this if all the parameters and files are the same......That is, in particular, the different nights all use the same flats (because the imaging train and flats did not change). If the different nights require different flats, then WBPP is not the way to go. You need to calibrate each night's individually. 

 

Alex


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#10 Dynan

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Posted 05 May 2021 - 10:37 AM

In APP you can assign any calibration frame to any session. It's a dream to work with.



#11 unimatrix0

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Posted 05 May 2021 - 12:03 PM

In APP you can assign any calibration frame to any session. It's a dream to work with.

Before I misunderstand this, you use APP of itself as the stacking /processing software, and not both APP and Pixinsight, correct? 
I'm using Siril lately, although it's very very beta if you ask me,  and doesn't have the script (or I don't see an option?) to use darkflats, which seems to work a lot better than bias frames. 

Not trying to jump to a different topic, but...
 

Also,  just have read this topic about issues with processing, and I believe I have a similar issue going on at the same time and I am also using ASI533 Mc pro with NINA.  Just to confirm this, I also used APT with the same camera and I know APT uses the ASCOM driver only for this camera, and there is a big difference between the subs. 



#12 Pelayo

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Posted 05 May 2021 - 12:22 PM

I usually take flats each night, even if I did not rotate the camera or anything else on the optical train. My concern are dust motes, am I being too scrupulous? My place can be really windy, although the thruth is I've never seen dust motes on my lights or flats. I think I am already answering to myself...

 

>>>>>1) Take new flats whenever you modify/rotate your imaging train or change exposure parameters

 

Unless I misunderstand, a change in the exposure parameters do not mean new flats are necessary. By that, I mean you can use the same flats on a 30 second exposure as on a 300 second exposure (as long as the imaging train did not change). And on a gain of 0 or a gain of 100. (Or ISO changes). The darks must change if you change those parameters, but they all use the same flats (as long as the imaging train is the same....and I suppose as long as the dust has not moved!!!).

 

  

>>>>>>I saw where you asked about PI being able to combine multiple nights. As Alex noted, the WBPP script does that,

Just to clarify, I think WBPP will do this if all the parameters and files are the same......That is, in particular, the different nights all use the same flats (because the imaging train and flats did not change). If the different nights require different flats, then WBPP is not the way to go. You need to calibrate each night's individually. 

 

Alex

It's possible to tell WBPP which lights go with which flats using keywords (date or session, for instance), but to be honest I didn't find it very friendly. I ended up calibrating separately. 


Edited by Pelayo, 05 May 2021 - 12:26 PM.


#13 Dynan

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Posted 05 May 2021 - 12:30 PM

I calibrate my images with APP. (Calibrate with darks, flats and biases, then stack lights)

 

I use Star Tools to process the final integration that comes out of APP. But I believe you can do much processing in APP though I've never done it.



#14 Alex McConahay

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Posted 05 May 2021 - 03:30 PM

I’ll admit I don’t know the fine points of WBPP and if you say it can, I stand corrected.

I don’t use that feature.

Alex

#15 schmeah

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Posted 05 May 2021 - 08:07 PM

I usually take flats each night, even if I did not rotate the camera or anything else on the optical train. My concern are dust motes, am I being too scrupulous? My place can be really windy, although the thruth is I've never seen dust motes on my lights or flats. I think I am already answering to myself...

Yes, I think you are being way too scrupulous, and I think that all who mentioned that they take a new set of flats every night are working way too hard. I have an in and out of the garage setup and often use the same set of flats for over six months. Even on the off chance that a dust mote or two shifts, it’s a matter of a few seconds to process it away. Take a new set after changing your imaging train or rotating your camera. Otherwise do it only when you notice a problem, which has been almost never for me.

 

Derek



#16 unimatrix0

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Posted 05 May 2021 - 09:04 PM

Yes, I think you are being way too scrupulous, and I think that all who mentioned that they take a new set of flats every night are working way too hard. I have an in and out of the garage setup and often use the same set of flats for over six months. Even on the off chance that a dust mote or two shifts, it’s a matter of a few seconds to process it away. Take a new set after changing your imaging train or rotating your camera. Otherwise do it only when you notice a problem, which has been almost never for me.

 

Derek

I'm getting water droplets usually. I can actually edit them out with photoshop if I just don't have the flats forgot to take them or I left the processing for weeks and can't remember which flats due to my messy, disorganized folders lately (I switched computers and wiped hard drives) 
Here is something else I noticed that no one mentions about creating an issue that needs flats and I noticed this with my own activity.

 

1. Dust caps needs to be super clean. Sometimes I introduce the dust by putting on/removing the dust cap and if the dust cap spent some time with the inner part up, guess what...  I usually blow it with compressed air before I put them back on. 

 

2. The usual white t-shirt rag method.  People don't realize that putting on/removing the white t shirt might be dropping lints or dust particles on their lenses. Seeing the junk on the stretched flat and being glad it's gone, but perhaps they just put them on when they put the rag on it! lol! 

I noticed this like the 3rd time I rubber banded a t shirt piece on my telescope.  Also where that T shirt piece is kept is important, because they attract and hold onto dust like a shop towel. 
Just some observations, that's why I don't like the t shirt method, I'm thinking about using my tracing board with a white sheet of paper on it. 


Edited by unimatrix0, 05 May 2021 - 09:06 PM.


#17 limeyx

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Posted 06 May 2021 - 04:08 PM

Yes, I think you are being way too scrupulous, and I think that all who mentioned that they take a new set of flats every night are working way too hard. I have an in and out of the garage setup and often use the same set of flats for over six months. Even on the off chance that a dust mote or two shifts, it’s a matter of a few seconds to process it away. Take a new set after changing your imaging train or rotating your camera. Otherwise do it only when you notice a problem, which has been almost never for me.

 

Derek

I get a lot of moving dust so it's mandatory for me or I would never get usable data. Maybe this is because my DSLR was used and has a bunch of dust in it.

 

Flats take about 10 mins so it's not a big hassle



#18 schmeah

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Posted 06 May 2021 - 07:38 PM

I get a lot of moving dust so it's mandatory for me or I would never get usable data. Maybe this is because my DSLR was used and has a bunch of dust in it.

 

Flats take about 10 mins so it's not a big hassle

So if you have that much moving dust, wouldn’t you have to take a flat after every x exposures, not just between imaging sessions? But I guess it’s easier with a DSLR. With a mono ccd I sometimes use five filters in a night.


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#19 limeyx

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Posted 06 May 2021 - 07:55 PM

So if you have that much moving dust, wouldn’t you have to take a flat after every x exposures, not just between imaging sessions? But I guess it’s easier with a DSLR. With a mono ccd I sometimes use five filters in a night.

I had one night when yes, the dust literally moved that much - between shots

 

Generally it stays put and flats taken at the end of the session are fine IF I leave the scope where it was (on the mount). I think sometimes just putting it down on a hard surface (even gently) can cause dust to move.

 

I suppose I could send it somewhere to get cleaned but often it comes back just as dirty


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