Images not stacking in alignment

[torrancemae]

I am doing photometry and have calibrated my images and done a virtual stack. When I am trying to place apertures on my stack of 10 images, 7 of the images are aligned while 3 of them are not, but are aligned with each other. I tried just moving my apertures in the moved images, but that moved the aperture in all the images. Is there a way that I can either fix the stack or move apertures in single images rather than all?

[karenacollins]

Some solutions for you to consider:

1) Are your original images plate solved? If so, enable the option "Use
RA/Dec to locate aperture positions" in the Multi-Aperture set up panel
and place the apertures on stars as desired in the first image. Then the
apertures will track the stars in the remaining images based on the WCS
coordinates in each image. In this case, run photometry on your original
images and no alignment is needed at all.

2) If you have WCS coordinates and still want to align the images first,
enable "Use RA/Dec to locate initial aperture positions". This method
requires no aperture placement.

3) If you don't have WCS coordinates, you might consider using the plate
solve function in AIJ or in another program and then follow steps 1 or 2
above.

4) If you don't want to deal with plate solving/WCS coordinates, when
you align images, the apertures should be larger than the largest
tracking/guiding error from one image to the next. It would be fine to
use one large aperture around a star that has no nearby neighbors of
similar brightness. The centroid needs to be able to find the same star
from one image to the next within the same aperture, but not be close
enough to another star such that it finds it rather than the intended star.

5) An alternate approach for non-plate-solved, non-aligned images is to
enable the "Single Step" mode in the Multi-Aperture setup panel. In this
mode, you place all of your apertures in the first image as normal and
then right click (or press enter), then in the second image just click
on the first star (i.e. the one with aperture T1), and continue that
process for all of your images. All of the apertures 2 through N will be
placed at the same distance from the first aperture and should find the
same stars in each image (assuming there is no significant image
rotation from one image to the next). If there is significant image
rotation from one image to the next, you will have to plate solve the
images first and use option 1 or 2 above.

Karen

[torrancemae]

Thank you! The first option worked for my plate solved images!

 

From: "karenacollins [via AstroImageJ]" <ml-node+[hidden email]>
Date: Saturday, July 9, 2016 at 5:21 AM
To: Tori Knapp <[hidden email]>
Subject: Re: Images not stacking in alignment

 

Some solutions for you to consider:

1) Are your original images plate solved? If so, enable the option "Use
RA/Dec to locate aperture positions" in the Multi-Aperture set up panel
and place the apertures on stars as desired in the first image. Then the
apertures will track the stars in the remaining images based on the WCS
coordinates in each image. In this case, run photometry on your original
images and no alignment is needed at all.

2) If you have WCS coordinates and still want to align the images first,
enable "Use RA/Dec to locate initial aperture positions". This method
requires no aperture placement.

3) If you don't have WCS coordinates, you might consider using the plate
solve function in AIJ or in another program and then follow steps 1 or 2
above.

4) If you don't want to deal with plate solving/WCS coordinates, when
you align images, the apertures should be larger than the largest
tracking/guiding error from one image to the next. It would be fine to
use one large aperture around a star that has no nearby neighbors of
similar brightness. The centroid needs to be able to find the same star
from one image to the next within the same aperture, but not be close
enough to another star such that it finds it rather than the intended star.

5) An alternate approach for non-plate-solved, non-aligned images is to
enable the "Single Step" mode in the Multi-Aperture setup panel. In this
mode, you place all of your apertures in the first image as normal and
then right click (or press enter), then in the second image just click
on the first star (i.e. the one with aperture T1), and continue that
process for all of your images. All of the apertures 2 through N will be
placed at the same distance from the first aperture and should find the
same stars in each image (assuming there is no significant image
rotation from one image to the next). If there is significant image
rotation from one image to the next, you will have to plate solve the
images first and use option 1 or 2 above.

Karen

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