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Auteur Sujet: Steps for aperture photometry  (Lu 21 fois)

DJOD

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Steps for aperture photometry
« le: avril 25, 2018, 09:45:47 09 »
Hi all

I am following the steps for doing aperture photometry, as per https://free-astro.org/siril_doc-en/#AperturePhoto_1

I see that step 5 is to Export the sequence, and step 6 is to Load the sequence (presumably from the exported data).  The question is "why?" - is there something that occurs when you export and re-import that does not happen when you just skip steps 5 and 6?

For information, I am supporting a girls high school here in Australia that has a robotic observatory, and they want to use Siril as the tool for imaging and photometry.  I'm working through the steps to be able to explain it to them in a stepwise process that teenagers can follow.

clear skies
David

lock042

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Re : Steps for aperture photometry
« Réponse #1 le: avril 25, 2018, 05:04:00 17 »
The exporting step is made to simplify the process. In order it allows to work with aligned sequences. If I well rememeber the video.

About the use of Siril in a robotic observatory, that is awesome :). Thanks for the news !!

DJOD

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Re : Steps for aperture photometry
« Réponse #2 le: avril 26, 2018, 01:29:17 13 »
Hi Lock

Yes, being able to provide astronomy training to teenage girls is rare in the schools.  They will learn to take and process images using Siril, and for the older girls we will teach science aspects like variable stars using the aperture photometry.

In your reply you said "it allows to work with aligned sequences".  The process I am documenting does the registration first, then allocating PSF for the sequence.  Is the export/import process required to align the images?

This is the process I am using:

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The process for registration is as follows:
   1. Select the Sequence tab.
   2. You can step through each of the images by clicking the + or - buttons.  The image will be shown in the second window.
   3. You can optionally exclude some images from the sequence (for example images of poor quality due to seeing or passing cloud).  To exclude an image click the Excluded checkbox.
   4. Select one of the images as the reference image by clicking the Reference image checkbox for that image.  Only one image can be the reference image in a sequence, setting it will unset the image previously set as reference.  If not set manually, the first image of the sequence is taken as reference.
   5. Select the Registration tab.
   6. On this tab, do the following:
      a. Click Register all images from sequence (unless you have excluded images as per above).
      b. In the Choose registration method select Global star alignment if it is not already chosen
      c. Click the Translation only checkbox
      d. Click the Go register button to start the registration process.

If sufficient stars exist in your images, the Output logs tab will show the data associated with them and indicate that the images have been successfully registered.
=====

Then I planned to go to the selection of the stars (V, 1, 2, 3 etc).

Or do I need to do the export followed by an import of the sequence to get the alignment working correctly? 

I appreciate your help, as I want to make sure the girls use Siril appropriately.

Clear skies
David
Brisbane, Australia


lock042

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Re : Steps for aperture photometry
« Réponse #3 le: avril 26, 2018, 01:54:58 13 »
OK I understand.
Choosing global registration is a bad idea for photometry. Because interpolation algorithm are applied to the image in order to rotate them.
Thus, we advice to use registration on one star. It will produce no more sequence but will save registration data in a seq file. However you need to find an isolated enough star and to make a selection as big the star moove. Except by checking "Follow star movement"
So now do photometry, you have two solutions:
- work on the sequence (it will be aligned on the fly)
- export the sequence and it will provide new files, i.e, a new aligned sequence and you will do photometry.

DJOD

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Re : Steps for aperture photometry
« Réponse #4 le: avril 29, 2018, 08:22:32 08 »
Hi Lock

Okay, thanks - I think I understand now.  In reality, it is probably not an issue - the scope is a Planewave 14" on an AP mount with autoguiding, so there shouldn't be much movement in the images!!

I will amend the instructions and see how the new process works out.  Keep you posted.

Regards
David