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Adding new subs to a previous imaging session

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#1 Desertanimal

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Posted 08 April 2021 - 01:52 PM

Using deep sky stacker.

 

Let's say I stacked 100 x 30 second images and got out "Saved tif A". 

 

Then I take 100 more shots another night... Can I put the new 100 images AND "saved tif A" into deep sky stacker? Will this give me "saved tif B"?

 

Can I even put a .tif into DSS?  

 

What if the new images are 60 seconds long? This leads to another general question. How do you stack subs of different lengths? Do you add all the subs to DSS, what about calibration frames? Do I need darks that match the exposure length of whatever subs I have?

 

I know I rattled off a bunch of questions very quickly. If there is a resource with this information? I will gladly do my own research, but of all the info that I have received lurking around here these are still unclear.

 

Thanks again for all the guidance!!    (Ha! see what I did there?)

 

 

Chris

 

 



#2 LightPollutedJim

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Posted 08 April 2021 - 02:13 PM

I'm interested in hearing thoughhts on this as well. Would you have to create a stacked "saved tif B" of the second 100 images, and then stack the two stacked files?

 

Jim


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#3 kevinbreen

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Posted 08 April 2021 - 04:50 PM

I start again and load all of the subs from both nights into DSS. DSS has no problem accepting subs of different length or ISO.
Not sure about the calibration frames though, good question
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#4 galacticinsomnia

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Posted 08 April 2021 - 05:10 PM

No, you don't include the saved tif.  Stack all your subs, and you will benefit more.

My own personal preference is to stack, to get an idea of where I am at.  Capture more data, and stack again, see if I have enough data with less noise, and just continue to grow the captured data.

Keep a library of your flats, bias, darks by Camera,Scope, ISO, Time, so they are easily incorporated.

If you are shooting the same target, with the same scope, there is no need to make calibration frames again.

Your milage may vary, but this is how I do it.

Clear Skies !!


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#5 deansjc

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Posted 08 April 2021 - 07:21 PM

It will be interesting to see where this thread goes.  DSS does not have a lot of use cases on its site and none that address this question in particular.  I've been looking for "the penultimate guide" on using DSS Groups.  If one exists, I haven't found it but surely it would address the OP's goals. 

 

There is one YouTube video that suggests that there is a bug related to any calibration frames placed into any group but the Main Group in that a master Dark does not get created.  The author vowed to remove the video if disproven.

 

Hopefully, anyone that has documented an approach for different objectives such as the OP's, they might share it.  The only use that I feel confident in is:

 

- one imaging session with all Light Frames of the same ISO

- managed within the Main Group only

- with associated calibration frames also in the Main Group.

 

I strongly believe DSS can do much more, but the documentation is pretty sparse, leaving users to too much trial and error.


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#6 deansjc

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Posted 08 April 2021 - 07:25 PM

Galacticinsomnia, I like where you are going, but from what I have read, flats do need to be re-shot for each successive group of light frames, unless and only if focus and camera rotation has not been touched between successive imaging sessions.  Do you agree?  Or is that point "over done".

 

If I am correct (basically restating what most APers suggest, a library of flats doesn't work.

 

Thoughts?

 

John


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#7 vidrazor

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Posted 08 April 2021 - 07:38 PM

If I'm not mistaken, DSS has provisions for session grouping. I've never used it, so I'm not sure what the process is, but each session can have it's own set of calibration frames.

#8 Desertanimal

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Posted 08 April 2021 - 07:44 PM

I've been using a single master flat, dark and bias frame for the last couple of stacks. But you can count my total number on your hands! hahaha.

Interesting that the answer to my question is so nebulous. I thought it would be a simple answer. I'm learning many AP things are not very clear cut.

What are other options for stacking and are they more difficult to use? (Nico, Elf...)

#9 vidrazor

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Posted 08 April 2021 - 09:38 PM

I've been using a single master flat, dark and bias frame for the last couple of stacks. But you can count my total number on your hands! hahaha.

Interesting that the answer to my question is so nebulous. I thought it would be a simple answer. I'm learning many AP things are not very clear cut.

What are other options for stacking and are they more difficult to use? (Nico, Elf...)

This was an excerpt someone took from the DSS manual:
https://www.cloudyni...-1531967166.jpg

So the MAIN group gets the offset/bias and the subgroups for each night get the lights, darks, and flats.

 

So the only thing not clear to me is if you just use one set of bias, or do you lump all the different nights together into one big pile? If it's only one set, I would imagine it should be the last one, as that's the present state of your camera.


Edited by vidrazor, 08 April 2021 - 09:48 PM.


#10 Mike in Rancho

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Posted 08 April 2021 - 10:45 PM

Hmm.  There's a multitude of questions and issues being tossed out here.  But, albeit not documented in a great way in their online manual and faq etc., DSS does exactly what it is supposed to, if you understand it and load your files properly.  I readily admit to doing it wrong early on when I first tried mutli-session imaging.  Also, you must make sure that what you are intending to do actually makes sense.  Otherwise you can just scramble your master files and end up with poor output.

 

First, you pretty much do not want to feed a finished stack back into DSS as a sub, to be combined with new individual subs.  There's a good chance it won't even work, especially if the image size no longer matches (from intersection mode, for example).  You also may have applied various settings in stacking that have altered the image significantly from what the subs are.  Finally, while you can do "stacks of stacks," I think it is generally considered best practice to load all individual subs in again as groups, in order to reap the benefits of your rejection algorithm.  The one caveat here is that you might be able to reuse masters.  That is not guaranteed, as there are changes that can result in new masters being needed.  For example, if you have a saved list and register it using bias frames, the other master calibration frames will incorporate that bias (or master bias), and overwrite them if masters already exist.  Those masters can no longer be used in a stacking scheme that does not include that bias (for example if you wanted to try it with dark flats in lieu of bias).

 

Finally, multi-session group stacking works fine, and all masters for each session are created appropriately.  Just remember that, for group stacking, any calibration frames in the main group will be applied globally.  And as noted above, if you set it up wrong, the application of those files can mangle your other masters.  In the usual scheme of things, which is same target over different nights, the only file you will have in Main is the bias or master bias.  And if you don't use bias, Main will probably be empty.  Then Group 1, 2, etc. will each have its own set of lights and associated calibration frames.  Also, it will behoove you to be organized with each night having its own folder, with subfolders within for lights and the different calibration subs.

 

You can even do a quick test of this if you set it up in some new folders, say 5 subs of each, and watch it work on the little window that pops up.  During registration it will go through and create masters for each group.

 

I believe it is still generally best to stack same exposures and iso even using groups.  It will allow you to do otherwise, but you have to make sure it is appropriately weighted if need be.  Or, you might be able to use one of the background calibration schemes so that the differing groups are stackable without the result being junk.

 

DSS does have an "entropy" stacking mode that is specifically made for combining different exposures and iso's.  I haven't tried it, so can't add anything there.  It may be something to try if that kind of "HDR" combination of exposures is what you are after.

 

Hope this helps.


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#11 Desertanimal

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Posted 09 April 2021 - 12:36 AM

Yes, that does help.

Thank you!

#12 deansjc

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Posted 09 April 2021 - 10:42 AM

Good post Mike, and a fair bit to digest - that's good.  It is more documentation than DSS puts up.

 

I note that you don't put lights in the Main Group.  How did you arrive at that?  I am leaning to start doing this, however at least a single night of imaging can safely be put into the Main group - lights and calibration frames.  At least DSS documentation suggests that.

 

Can you confirm that that DSS is creating and saving the correct master calibration files in the File Group that they were placed in?

 

My last read of the DSS "rules" is that calibration frames in the main group apply to other groups, however, if other groups have their own calibration frames, then would DSS not apply these instead, and only go to the main group if there are none in the specific group?

 

(It's a bit awkward to even pose the question here....'hope my query is clear at least :-)

 

'Appreciate your further input here.  

 

John


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#13 Mike in Rancho

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Posted 09 April 2021 - 05:35 PM

Good post Mike, and a fair bit to digest - that's good.  It is more documentation than DSS puts up.

 

I note that you don't put lights in the Main Group.  How did you arrive at that?  I am leaning to start doing this, however at least a single night of imaging can safely be put into the Main group - lights and calibration frames.  At least DSS documentation suggests that.

 

Can you confirm that that DSS is creating and saving the correct master calibration files in the File Group that they were placed in?

 

My last read of the DSS "rules" is that calibration frames in the main group apply to other groups, however, if other groups have their own calibration frames, then would DSS not apply these instead, and only go to the main group if there are none in the specific group?

 

(It's a bit awkward to even pose the question here....'hope my query is clear at least :-)

 

'Appreciate your further input here.  

 

John

No, I do understand your final query there, but I don't know if DSS can quite read into things that way.  Possible?  They do have groups where the developer will answer more complex questions, and it might be good to know just how "smart" DSS is in trying to decipher how a user loaded files in.

 

The website organization does leave something to be desired as far as navigation.  But if you can find it, there is a nice graphic flowchart, as well as descriptions, of how the various masters are created and then applied.  Bottom line though, if anything changes, the master is probably no longer appropriate.  Bias is the easiest, since they are only a result of the bias frames.  So I do keep an archive of those for reuse.  However, if you ever change any settings in your RAW/FITS window, then that master bias would no longer match up.  Similar concepts with darks and dark flats.  They are made from the individual subs, but, the already created master bias is subtracted off each frame during creation.  And the master flat is yet another step more complicated, plus there is scaling to the lights.  Which is why you can take flats at all sorts of different brightness levels, and it still works.  In any event, you will still get a stacked output no matter what you use, but query whether you end up with the calibration you were trying to achieve.  Thus, when reusing masters from before, just make sure all settings are identical.  If I'm ever not sure, I just load in the subs that went into creating a master (since I archive those too) and re-run it.  Seems safer then guessing.

 

Yes single night can all go in the main group.  I've never had any issues with that, and as you note that's what DSS tells you to do.

 

As to whether the masters are created in the file group...I think so?  I mean I don't know what the program is doing internally, but I can confirm (just tested last night) that when you run registration, if your multi night groups are properly set up, it will create a master-whatever .tiff file in the subfolder where those individual files were found.  Now, I keep all my separate subs in separate subfolders, so I haven't tested what DSS might do if it tried to make two different masters, from different underlying files, but within the same folder.  Maybe it adds a number to it, same way it does on the autosave?  But for the other part of your question, yes, DSS also creates a text file along with the master.  You can open it in Notepad and it describes exactly how the master was made, including the names of all the subs that were used to make it.

 

Nothing beats a little experiment though - for your more complicated queries, just take some old files and copy a few into some new folders for running tests.  Post up what you find.  I'm always curious to learn more about what DSS might be doing in trickier situations.


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#14 Desertanimal

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Posted 09 April 2021 - 07:52 PM

Wow, this turned into an interesting discussion. I'm pretty new so it's easy to try different things in dss.

Question though as a noob. What would I see as different when I create stacks with only masters, or calibration subs etc? Would I just get a subpar autosave in the end? Will I notice more when I start stretching etc? In general, what am I looking for?

#15 galacticinsomnia

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Posted 09 April 2021 - 07:53 PM

Galacticinsomnia, I like where you are going, but from what I have read, flats do need to be re-shot for each successive group of light frames, unless and only if focus and camera rotation has not been touched between successive imaging sessions.  Do you agree?  Or is that point "over done".

 

If I am correct (basically restating what most APers suggest, a library of flats doesn't work.

 

Thoughts?

 

John

Thank you, my life and use experience is limited and I won't pretend to know something I don't, because I don't know how DSS will handle many situations.

For me though, what I have found to give Decent, not perfect, results, is to actually make master flats, it isn't easy, but so far has worked for me and saves me a lot of time, and the results are comparible to just shooting them at the time of imaging.

Break down my flats by Camera--->Scope--->ISO's.
For each camera, there can be many scopes, and for each scope, can be many cameras, so I chose to make an order like this.
Canon T6s-
          SVbony 503
                  Iso100
                  Iso400
                  Iso800
                  Iso1600
         IOprton RC6
                  Iso100
                  Iso400
                  Iso800
                  Iso1600
Canon M6ii
          SVbony 503
                  Iso100
                  Iso400
                  Iso800
                  Iso1600
         IOprton RC6
                  Iso100
                  Iso400
                  Iso800
                  Iso1600

My image train is shot pretty much the same in each session, and the amount of variable is negligable.
Flats, Darks, and Bias are made in the same way, I run an automated session Jan 1, Apr 1, July 1, Oct 1.

I know there is a lot of Nay Say on this, but so far it works for me :) 

Between these and my dithering, I'm pretty well covered. 

Hope this helps someone or at least makes it easier for someone, or more enjoyable.

Clear Skies !!


 


Edited by galacticinsomnia, 09 April 2021 - 08:02 PM.

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#16 vidrazor

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Posted 09 April 2021 - 07:55 PM

Hmm.  There's a multitude of questions and issues being tossed out here...

Hope this helps.

Reading the except from the manual that someone posted in a different thread, it appears that lights, darks, and flats from each session belong in the sub groups, and only files that should be in the MAIN GROUP are bias files. However if you shot bias on all your evenings, do you lump them together, or do you use one set for all? If one set, do you use the most recent? This would seem to make sense to me, but I'm not sure.


Edited by vidrazor, 09 April 2021 - 07:57 PM.

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#17 galacticinsomnia

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Posted 09 April 2021 - 08:42 PM

Reading the except from the manual that someone posted in a different thread, it appears that lights, darks, and flats from each session belong in the sub groups, and only files that should be in the MAIN GROUP are bias files. However if you shot bias on all your evenings, do you lump them together, or do you use one set for all? If one set, do you use the most recent? This would seem to make sense to me, but I'm not sure.

I think creating a bunch of calibration fames each session is more likely to be a waste of resources with diminishing returns to a point.
 

All cameras wear out.
A dslr, has a shutter life, a one shot camera has a sensor life.  You can calculate how many lights your taking, against expected failure, and get a cost per shot, and when you realize you are using your gear and 3/4 of your shots are calibration frames, then I have to think there has to be a better and more efficient way, either by method of the idea of calibration, or software, or better capturing in the first place.

I know this isn't applicable, but a sports photographer friend of mind, practiced, Pray and Spray, shooting as many frames as he could as fast as he could, instead of following the scene and shooting wisely.  My friends 3k DSLR died on the field less than 18 months after purchase, while my 10 year old DSLR was still getting wonderful captures.

I can't in good conscience recommend a process just because a bunch of folks use it.  I can however encourage experimentation so people can find out what works better for them.

Clear Skies !!


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#18 galacticinsomnia

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Posted 09 April 2021 - 08:58 PM

I started using Siril a while back, and it's worth it to give it a try.
Put your images into the folders, and run a simple script and play with the results.

DSS is the classic, I still have it, still use it, but there is some real amazing things happening in Siril that DSS just doesn't do.

I love the scripts and the scripting engine, command line tools, etc.
The colormetrics, background removal, banding fix, green color cast fix, and so many more.

 

Clear skies!!


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#19 Mike in Rancho

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Posted 10 April 2021 - 04:21 AM

Wow, this turned into an interesting discussion. I'm pretty new so it's easy to try different things in dss.

Question though as a noob. What would I see as different when I create stacks with only masters, or calibration subs etc? Would I just get a subpar autosave in the end? Will I notice more when I start stretching etc? In general, what am I looking for?

Hmm, I don't quite follow the question.  If nothing has changed, the result will be the same.  But I may not be understanding what you mean.

 

So, if you register a session and stack it, then take that same file list and replace all the individual calibration subframes with the masters that were made from them...identical.

 

In fact, if your run registration separately from stacking - which I always do - and you make no changes, when DSS stacks it will jump right to stacking using the masters it just created.  No need to do double work.



#20 Mike in Rancho

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Posted 10 April 2021 - 04:25 AM

Thank you, my life and use experience is limited and I won't pretend to know something I don't, because I don't know how DSS will handle many situations.

For me though, what I have found to give Decent, not perfect, results, is to actually make master flats, it isn't easy, but so far has worked for me and saves me a lot of time, and the results are comparible to just shooting them at the time of imaging.

Break down my flats by Camera--->Scope--->ISO's.
For each camera, there can be many scopes, and for each scope, can be many cameras, so I chose to make an order like this.
Canon T6s-
          SVbony 503
                  Iso100
                  Iso400
                  Iso800
                  Iso1600
         IOprton RC6
                  Iso100
                  Iso400
                  Iso800
                  Iso1600
Canon M6ii
          SVbony 503
                  Iso100
                  Iso400
                  Iso800
                  Iso1600
         IOprton RC6
                  Iso100
                  Iso400
                  Iso800
                  Iso1600

My image train is shot pretty much the same in each session, and the amount of variable is negligable.
Flats, Darks, and Bias are made in the same way, I run an automated session Jan 1, Apr 1, July 1, Oct 1.

I know there is a lot of Nay Say on this, but so far it works for me smile.gif 

Between these and my dithering, I'm pretty well covered. 

Hope this helps someone or at least makes it easier for someone, or more enjoyable.

Clear Skies !!


 

That's pretty interesting.  And if it works, great!  Probably can't calibrate out changing dust spots, but for vignetting it should.  There have been times when I got myself in a bind, and pulled out similar flat frames from a different session.  Same concept, I just haven't archived any master flats.

 

The only thing you might have to worry about is rotation.  Camera lenses are probably safe, since they always click into place in the exact same orientation always.  Scopes might be a bit trickier to ensure the vignetting field of your master flats matches that of your sets of lights?  Or do you have a method to ensure the same camera-scope orientation each time?


Edited by Mike in Rancho, 10 April 2021 - 04:26 AM.

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#21 Mike in Rancho

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Posted 10 April 2021 - 04:37 AM

Reading the except from the manual that someone posted in a different thread, it appears that lights, darks, and flats from each session belong in the sub groups, and only files that should be in the MAIN GROUP are bias files. However if you shot bias on all your evenings, do you lump them together, or do you use one set for all? If one set, do you use the most recent? This would seem to make sense to me, but I'm not sure.

Well, as to the first part - yes I think it is the most common case that Main would only hold the bias frames - or your prefab master bias.  But it depends.  Some people might have master darks that would apply to all groups and so could go in Main.  And galacticinsomnia just noted he archives his master flats.  So it really depends.  As was noted, as long as you know that settings aren't different, the masters should work out.

 

Second question has me perplexed, however.  Since bias has no relation to any shooting option or environmental condition - i.e. exposure, temperature, and is taken at the camera's fastest speed and most likely with the body cap on...why would bias be taken for each session?  My understanding is the bias level lasts a long time.  I haven't taken any new ones other than if I add a new ISO I've not shot at before, or I decide I want to add more subs.  I try for 50 frames to make a master bias.  I know there's some charts out there that show how the bias gets better with more subs, like 100 or 150.  But, eh, I just stopped at 50 lol.


Edited by Mike in Rancho, 10 April 2021 - 02:12 PM.


#22 Mike in Rancho

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Posted 10 April 2021 - 04:40 AM

I started using Siril a while back, and it's worth it to give it a try.
Put your images into the folders, and run a simple script and play with the results.

DSS is the classic, I still have it, still use it, but there is some real amazing things happening in Siril that DSS just doesn't do.

I love the scripts and the scripting engine, command line tools, etc.
The colormetrics, background removal, banding fix, green color cast fix, and so many more.

 

Clear skies!!

Interesting.  Maybe I'll take a look.  What's one more AP program on the laptop anyway?

 

The only thing is I post-process with Startools, and if those are all preprocessing features you are talking about, ST heavily frowns upon use of them.


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#23 vidrazor

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Posted 10 April 2021 - 05:43 AM

...Second question has me perplexed, however.  Since bias has no relation to any shooting option or environmental condition - i.e. exposure, ISO, temperature, and is taken at the camera's fastest speed and most likely with the body cap on...why would bias be taken for each session?  My understanding is the bias level lasts a long time.  I haven't taken any new ones other than if I add a new ISO I've not shot at before, or I decide I want to add more subs.  I try for 50 frames to make a master bias.  I know there's some charts out there that show how the bias gets better with more subs, like 100 or 150.  But, eh, I just stopped at 50 lol.

Well I wasn't sure if bias are affected by the temp of the camera at any given session, or if the sensor "ages" over time and the spec changes, hence thinking the most recent set would be the best to use.


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#24 Mike in Rancho

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Posted 10 April 2021 - 02:13 PM

Well I wasn't sure if bias are affected by the temp of the camera at any given session, or if the sensor "ages" over time and the spec changes, hence thinking the most recent set would be the best to use.

Oops.  You do take bias for each ISO of course, I edited and fixed that.  Temp no, aging yes.  I think they say 6 months to a year?



#25 galacticinsomnia

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Posted 10 April 2021 - 03:50 PM

Interesting.  Maybe I'll take a look.  What's one more AP program on the laptop anyway?

 

The only thing is I post-process with Startools, and if those are all preprocessing features you are talking about, ST heavily frowns upon use of them.

It's definitely made a huge impact for me.  It isn't the only software I use, but it is rapidly becoming my goto for preprocessing.

Still need to run Affinity Pro to see how that "stacks" up ;)    Sorry couldn't help myself.

Most of my dust and hotpixels, are removed by the Dithering. 
Rotation I don't really content with much.  Using a DSLR I keep it generally set where it is lined up the same each time, and honestly, I haven't used any other scope but my Svbony 503 since I got it, and haven't even taken the camera off, except to change filters.
So rotation is negligible.   Are there any other concerns I should have by having a calibration Library?
Clear Skies.


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