Atik 460 subs orientation question

[assouptro]

Hi all

I have been busy taking 20min subs of ngc6960 for the passed couple of months now and I want to produce the best stack I can but I have realized I definitely had rotate 180 degrees ticked on a few subs. This obviously presents a problem when applying flats darks and bias. Is there a way of finding out which subs are orientated 180? There doesn't seem to be anything in the file information to indicate which way the sub has been orientated. 

It should be simple, I should just be able to look at them and see which way round they are but I flipped a few times passed the meridian and  not always straight away so unless I do some detective work with dates and times comparing cartes du ciel etc  it isn't obvious!

Do I have to do the detective work and then stack the reversed subs separately with correctly orientated calibration frames then stack the results in something like photoshop?

I am just starting to play with astropixel processor and its become obvious to me I need to stick to 1 orientation. The thing is, I sometimes 'flip' the image to check the framing and have been known to forget to untick the rotate button!! 🙄

Any help or suggestions will be great thanks 

Bryan

[whipdry]

Only thing I can suggest is do a 20 min dark frame adjust the histogram so just the hottest pixels are viable then blink with the light frames and see if you get a match... not tried this myself. 

Peter

[assouptro]

6 minutes ago, whipdry said:

Only thing I can suggest is do a 20 min dark frame adjust the histogram so just the hottest pixels are viable then blink with the light frames and see if you get a match... not tried this myself. 

Peter

Hi Peter

Thanks for taking the time to respond to my question.

It's definitely an idea!

I was hoping someone could tell me a way of identifying the rotated subs via software or some kind of file marker but if that's not possible then your suggestion is probably the next best option and a good one at that!

Cheers 

Bryan

[whipdry]

2 minutes ago, assouptro said:

Hi Peter

Thanks for taking the time to respond to my question.

It's definitely an idea!

I was hoping someone could tell me a way of identifying the rotated subs via software or some kind of file marker but if that's not possible then your suggestion is probably the next best option and a good one at that!

Cheers 

Bryan

Just tried it on my One9.0 subs zoomed in on the hottest pixel on the dark and blinked a Ha sub and it's shows the hot pixel in the same place... funny I never thought to do this when I had the same issue so thanks for the question. 

Peter

[assouptro]

1 minute ago, whipdry said:

Just tried it on my One9.0 subs zoomed in on the hottest pixel on the dark and blinked a Ha sub and it's shows the hot pixel in the same place... funny I never thought to do this when I had the same issue so thanks for the question. 

Peter

It just goes to show.... sometimes you can solve a personal problem by giving advice to someone else with a similar issue!

[ollypenrice]

'Rotate 180' in Artemis does require rotated calibration files. A meridian flip doesn't. On the other hand a meridian flip does require the stacking software to know that a rotation of the calibrated image is necessary. Mine, Astro Art, needs to be told to support rotation up to 180 degrees. Some just do it without being asked.

Because of the danger of forgetting, I never use 'rotate 180' in Artemis. Instead I open the earlier image I'm using as a framing reference in another package and rotate that so it matches the incoming images.

Olly

[kirkster501]

It took me ages to get my head around this too.   Remember that when a flip occurs, it doesn't matter; the sensor is still aligned to the optics of the telescope/lens in the same way.  It doesn't matter if you turn the scope upside down, back to front or whatever, the fact is that the sensor is still in the same place with respect to the telescope optics.  So the flats do not change.  The imaged subject has rotated 180 degrees, not the alignment of the optics themselves.  So the dust bunnies will have moved 180 degrees with respect to the image, not the optics.  Software like Pixinsght can stitch all this together automatically since as Olly says it can work this out.

The slightest movement of the camera sensor with respect to the optics requires a new set of flats, strictly speaking.  I can get away with reusing the flats from previous sessions as long as the camera is left on the scope and is covered between imaging runs (so that new bunnies do not appear and they shouldn't because most of them are near to the sensor and not on the telescope objective).  I do indeed do this for a few nights worth of imaging runs if this is the case.  But the camera must not move with respect to the telescope.

It is incredibly annoying to collect a quality set of lights and forget to get the associated flats.  I have several data sets ruined that way and have had to resort to complex and much inferior photoshop hacks to get rid of dust bunnies and vignetting that flats would have sorted out at step one calibration phase!

Edited October 12, 2019 by kirkster501

[gorann]

This is usually no problem at all if you use Pixinsight for the stacking (which I do before I start processing in PS). PI will automatically recognize 180° turned images during star alignment of the subs. What you do before star aligning your subs is the calibration of the "unturned" subs using a master dark, master flat, master bias, or whatever you want to use for the calibration (it is important that you do this on unturned subs so the chip is oriented the same way as in your calibration frames). So work flow is: Calibrate your images as they are now (so unturned) -> Star align them (called Image Registration in PI and they are automatically turned by PI in the same direction as the reference image that you have picked in your stack) -> Stack them into one image (called Image Integration in PI). If you have OSC data then you have to do debayering  after calibration but before star alignment.

[carastro]

If you use Pixinsight then is seems from what has been posted above that will sort it out.

I don't use Pixinsight and sometimes have the same problem.  When I capture I try to remember to write FLIP on the flipped file names, but I don't always remember to do this.  So what I do is examine the star patterns of the subs before I stack them and then either rotate them before stacking, (calibration will still be the same as explained above), or stacking the flipped and unflipped separately and then stack the stacks.  

But to do this you do need some sort of software to be able to examine the fits files.  If you don't have software that will enable this, you could download fits liberator.

Carole 

[david_taurus83]

1 hour ago, gorann said:

This is usually no problem at all if you use Pixinsight for the stacking (which I do before I start processing in PS). PI will automatically recognize 180° turned images during star alignment of the subs. What you do before star aligning your subs is the calibration of the "unturned" subs using a master dark, master flat, master bias, or whatever you want to use for the calibration (it is important that you do this on unturned subs so the chip is oriented the same way as in your calibration frames). So work flow is: Calibrate your images as they are now (so unturned) -> Star align them (called Image Registration in PI and they are automatically turned by PI in the same direction as the reference image that you have picked in your stack) -> Stack them into one image (called Image Integration in PI). If you have OSC data then you have to do debayering  after calibration but before star alignment.

Not quite sure I understand this. Star aligning will reference all images off a single frame. It will also move any dust bunnies and vignetting so cant be used to align the frames before calibrating.

[gorann]

32 minutes ago, david_taurus83 said:

Not quite sure I understand this. Star aligning will reference all images off a single frame. It will also move any dust bunnies and vignetting so cant be used to align the frames before calibrating.

Maybe it is different in the program you use, but in PI image calibration (against darks, bias and flats to remove dust bunnies) is done first in a separate step from star alignment (which will rotate images that are upside down after a flip). After a flip it is only the image of the sky that is turned, not the chip in relation to the optical train, so the same darks, bias and flats apply before and after a flip,

[david_taurus83]

I do use Pixinsight but if I understand correctly, Bryan doesn't know which images are flipped between either a meridian flip or the rotate 180° function in Artemis. So he cant calibrate as he needs to match the Artemis flipped lights with Artemis flipped flats, darks and bias.

As already mentioned, I think the best option is to manually inspect each sub and match the sub to a corresponding calibration sub with matching hot pixels.

[ollypenrice]

1 hour ago, carastro said:

If you use Pixinsight then is seems from what has been posted above that will sort it out.

I don't use Pixinsight and sometimes have the same problem.  When I capture I try to remember to write FLIP on the flipped file names, but I don't always remember to do this.  So what I do is examine the star patterns of the subs before I stack them and then either rotate them before stacking, (calibration will still be the same as explained above), or stacking the flipped and unflipped separately and then stack the stacks.  

But to do this you do need some sort of software to be able to examine the fits files.  If you don't have software that will enable this, you could download fits liberator.

Carole 

What do you use for stacking, Carole?

Olly

[carastro]

Quote

What do you use for stacking, Carole?

Astroart.  I expect you're going to tell me that Astroart will rotate them.  But I have never explored the various settings in AA, so if there is a way, please elucidate.

I am sure it can also read fits files, but I tend to use Maxim for that as the Fits header is always helpful. 

Thanks

Carole 

 

Edited October 12, 2019 by carastro

[ollypenrice]

17 minutes ago, carastro said:

Astroart.  I expect you're going to tell me that Astroart will rotate them.  But I have never explored the various settings in AA, so if there is a way, please elucidate.

I am sure it can also read fits files, but I tend to use Maxim for that as the Fits header is always helpful. 

Thanks

Carole 

 

I thought you did. It's dead easy from (I think) AA5 onwards. Go to the second page of the Pre-processing window and 1) choose auto alignment, then 2) Star pattern, translation and rotation and then 3) type in 180 for the max rotation. The screen grab is from AA6 but AA5 is almost the same. The third step is easy to identify, it just requires the maximum permitted rotation to be 180 degrees. This will save you an awful lot of faffing about.

A note on terminology: a meridian flip, confusingly, makes a rotated image and not a flipped one. A flipped image is a mirrored one. Some capture software does produce flipped output files, which is rather silly!

Olly

PS Correction: It seems you have to uncheck 'Automatic Settings' to make the third step. I always do so anyway because I prefer to up the number of alignment stars to the maximum allowed.

Edited October 12, 2019 by ollypenrice
PS

[carastro]

Thanks Olly, I do use this function, but when it said rotate, I assumed it meant amounts less than 180 degrees, i.e if you had set up on two different nights and didn't quite get the orientation of the camera the same.   So I was doing 1 & 2, but not 3.

Will give that a try.  Thanks.

Carole 

[gorann]

44 minutes ago, david_taurus83 said:

I do use Pixinsight but if I understand correctly, Bryan doesn't know which images are flipped between either a meridian flip or the rotate 180° function in Artemis. So he cant calibrate as he needs to match the Artemis flipped lights with Artemis flipped flats, darks and bias.

As already mentioned, I think the best option is to manually inspect each sub and match the sub to a corresponding calibration sub with matching hot pixels.

Now I am confused. What is a flipped flat and why would anyone flip a flat? If the camera has not be rotaded the flats would be the same before and after a meridean flip.

[david_taurus83]

6 minutes ago, gorann said:

Now I am confused. What is a flipped flat and why would anyone flip a flat? If the camera has not be rotaded the flats would be the same before and after a meridean flip.

I have never used Artemis but it appears you can tick a box so the software will output the file rotated 180°.

[assouptro]

1 minute ago, gorann said:

Now I am confused. What is a flipped flat and why would anyone flip a flat? If the camera has not be rotaded the flats would be the same before and after a meridean flip.

That camera has an option to rotate the image 180 degrees which can be useful do alignment with a previous imaging session especially after a meridian flip, the problem is, if you forget to uncheck the rotate camera option then the subs will  be “upside down” in relation to your calibration frames. A flipped flat would be a flat taken with the rotate camera option checked so you can calibrate the frames taken “by accident’ the problem I have, as David kindly pointed out, is identifying the images that have been taken in the rotate mode as they look the same as images taken before the meridian. 
I hope that makes sense? 
cheers 

Bryan

[assouptro]

Just a quick thanks to everyone for contributing to this thread 

I am learning a lot, mainly about pixinsight and AstroArt, which I don’t personally use, I am just trying to get my head around astro pixel processor, but I may take a look at these other programs! 
 

thanks again 

Bryan 

[ollypenrice]

30 minutes ago, carastro said:

Thanks Olly, I do use this function, but when it said rotate, I assumed it meant amounts less than 180 degrees, i.e if you had set up on two different nights and didn't quite get the orientation of the camera the same.   So I was doing 1 & 2, but not 3.

Will give that a try.  Thanks.

Carole 

It was the big gap in AstroArt's stacking features. I don't know why it doesn't default to a max of 180 degrees since I'm sure most users would want this. More people will be doing meridian flips than getting their camera orientation out by a mile - surely!

Olly

[david_taurus83]

16 minutes ago, assouptro said:

That camera has an option to rotate the image 180 degrees which can be useful do alignment with a previous imaging session especially after a meridian flip, the problem is, if you forget to uncheck the rotate camera option then the subs will  be “upside down” in relation to your calibration frames. A flipped flat would be a flat taken with the rotate camera option checked so you can calibrate the frames taken “by accident’ the problem I have, as David kindly pointed out, is identifying the images that have been taken in the rotate mode as they look the same as images taken before the meridian. 
I hope that makes sense? 
cheers 

Bryan

Bryan, you say there is nothing in the file information. Do you mean the FITS header?

[ollypenrice]

14 minutes ago, assouptro said:

Just a quick thanks to everyone for contributing to this thread 

I am learning a lot, mainly about pixinsight and AstroArt, which I don’t personally use, I am just trying to get my head around astro pixel processor, but I may take a look at these other programs! 
 

thanks again 

Bryan 

If you have APP I'm not sure that AstroArt will add much. Does APP have a 'repair line' feature? This is very good for getting rid of satellite trails and is a big help with planes, though not infallible.

Olly

[assouptro]

15 minutes ago, ollypenrice said:

If you have APP I'm not sure that AstroArt will add much. Does APP have a 'repair line' feature? This is very good for getting rid of satellite trails and is a big help with planes, though not infallible.

Olly

To be absolutely honest Olly I don't know if it does? I am just getting to grips (and that's a loose grip!) with it's basic registration, calibration and integration routines! 

It seems quite powerful and the results so far have looked promising but in the future I need to resist the temptation to rotate the camera as I have just caused myself extra unnecessary work after hours of cloud and shower dodging!  

Bryan

Edited October 12, 2019 by assouptro

[assouptro]

20 minutes ago, david_taurus83 said:

Bryan, you say there is nothing in the file information. Do you mean the FITS header?

Hi David

I am not entirely sure what the FITS header is? I have been referring to the filename or the image properties but if there is more information hidden in the FITS that can possibly help I'd be interested in learning about it!

Cheers 

Bryan