Author Topic: Misaligned stars??  (Read 339 times)

Offline alanrock

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Misaligned stars??
« on: 2019 May 05 18:57:33 »
After running a star alignment, and doing a channel combination on the registered RGB images, some of my stars are not lined up correctly (I think). Please take a look at the attached image (which is taken from a tiny preview from the image) and tell me what you think I could be doing wrong. Any processing that takes place on the resultant image just seems to either magnify the problem or create other weird artifacts.

Offline pfile

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Re: Misaligned stars??
« Reply #1 on: 2019 May 05 19:54:44 »
there are a lot of reasons why this can be caused by the particular optics of your telescope.

what kind of telescope are you using, and is this at one of the edges of the frame, or on axis?

rob

Offline STEVE333

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Re: Misaligned stars??
« Reply #2 on: 2019 May 05 19:57:49 »
I have that problem with my ES ED102 telescope. It is a problem with my telescope optics (and maybe your too) and not with the aligning of the combined RGB images. The R/G/B images do not all line up properly in the original images.

I have had some success with the following approach:
1) Split the stacked image into the separate R/G/B images.
2) Open StarAlignment and put the G image as the Reference image and put the R and B images into the Target images window.
3) Click on the Apply Global button (round button at the bottom of the StarAlignment window). It will create a new registered version of the R and B images (with _registered attached to the name).
4) Open ChannelCombination and make sure the RGB Color Space is selected.
5a) Select the R registered image for the R channel.
 b)  Select the original G image for the G channel.
 c)  Select the B registered image for the B channel.
6) Click on the Global Apply button and a new image will be created. Hopefully the RGB channels will be better aligned in this new image.

Hope this helps at least some.

Steve
Telescopes:  WO Star71 ii, ES ED102 CF
Camera:  Canon T3 (modified)
Filters:  IDAS LPS-D1, Triad Tri-Band, STC Duo-Narrowband
Mount:  CEM40 EC
Software:  BYEOS, PHD2, PixInsight

http://www.SteveKing.Pictures/

Offline alanrock

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Re: Misaligned stars??
« Reply #3 on: 2019 May 05 20:43:11 »
It's a Celestron 9.25" SCT. It doesn't seem to only be at the edge of the image, I've attached one from the center.

Offline pfile

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Re: Misaligned stars??
« Reply #4 on: 2019 May 05 21:25:31 »
any reducer in the mix? is this an OSC camera?

rob

Offline alanrock

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Re: Misaligned stars??
« Reply #5 on: 2019 May 05 21:54:16 »
Im using a ZWO1600 mono camera. Optolong RGBL filters. Starizona 0.63x SCT corrector/focal reducer.

Offline pfile

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Re: Misaligned stars??
« Reply #6 on: 2019 May 06 10:18:08 »
OK - in this case i would follow steve's advice. refracting elements can cause issues like this depending on the quality of the optics (and how well they match the telescope they are paired with.)

rob

Offline msmythers

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Re: Misaligned stars??
« Reply #7 on: 2019 May 06 10:56:27 »
You can also try the Channel Match tool if all color separations are in the same direction. If you have problems in the corners with the directions being different I've used StarAlignment tool with distortion correction turned on. First separate your image to the individual R,G and B channel images. Use one of those as the reference, I generally use green and align the other two images to the reference.


Mike

Offline MikeOates

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Re: Misaligned stars??
« Reply #8 on: 2019 June 04 05:56:35 »
There is another cause for this and it's what happens to my images. If I take R G & B subs (mono camera) and one or more were taken on one side of the meridan and one or more on the other side, they don't line up.

A fudge that has limited success is the Channel Match tool as already mentioned.

But the best method is to ensure I take all R G & B images on the same side of the meridan. It does not seem to matter with narrowband images, perhaps because they are "narrowband" and the optics can cope better.

I have never got round to sorting out the real cause which is probably some optical misalignment due to optics or focuser movement in the scope. I know it's not ideal, but I have managed for a few years now and I really don't want to send the scope back to Japan for checking and re-collimating!

Mike