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M51 with Meade 14" LX850


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A few clear nights in May and 12.5 hours of data.  I struggled with gradients in my last image (M100).  I have that problem solved but I have stars that have color that is not aligning resulting in red and green bloated stars.  Details here https://www.astrobin.com/ezw9bq/

Qhy 268M 

Mesu 200 MKII


Baader RGB 36mm




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Beautiful image. Regarding the bloat, I sometimes have to scale my green to match my red, only change it around under and up to 1 percent of width/height then they usually align near enough. A star selection, expand region around star and slight blur then blends any CA out.

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PI probably does it automatically, in PS it's fairly easy to do:

If you've got your rgbwhatever layers in PS, select the layer you want to resize, make sure it's on top of a reference layer you are scaling to, change its opacity to something like 40 percent so you can see both layers, and go to edit > transform > scale, at the top under the menu bar you'll have the dimensions of the layer with a rotation option etc, just increase or decrease the width and/or height by a set percentage ie 99 would correspond to a 1 percent reduction from the original. Usually you only need a point change like 99.8, 99.7, 100.2 for example. Press enter twice once done. Check your rotations match also as this is guaranteed to be off if you've shot different sessions. 

Star bloat maybe best to do once all the layers are flattened or at least the RGB into one colour layer, also make sure any border edge mismatch from stacking or aligning is removed by cropping down the image first. Then:

1. Select > colour range

2. Choose highlights, I doubt you'd need to adjust any sliders, you may need to depending on the version of PS to select more or less but on highlights it normally selects all the white bright areas.

3. Your stars should now be all highlighted by dashed lines circles.

4. You now want to expand the selection region to account for haloing around the stars, go to select > modify > expand, and input a pixel value in the dialogue box which will expand the circles to encircle the most bloated stars, I usually use a value of 6-8. The star selection circles should now be slightly larger.

5. Now you want to feather the selections so there's a soft transition from the original image to the stars being altered so go to select > feather and input a pixel value which is half of the value you used to expand the region.

6. Then go to filter > blur > Gaussian blur, input something which just blurs the CA around the stars but not making the stars a completely blurred white splodge.

I think that's it.

You can also do this process to reduce your star sizes prior to blurring them, instead of step 6 you instead goto filter > other > minimise, a pixel value of 1 or 2 usually does it. It should be subtle enough so that your masses of 1 pixel like stars fade a little into the background, it's not an essential step but draws more attention to the target you're imaging. Then you can do the above to blur any CA around the stars.



Edited by Elp
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