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Thread: Bright stars have different colors

  1. #1
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    Default Bright stars have different colors



    Hi, anyone see this before? Happens to most of my images, mainly bright stars. I have a 480mm triplet. Asi 1600mm c. Zwo filters ( lrgb) this image used gain 76, 30 seconds each (about 275 frames each channel) . I use darks, flats and dark flats. You can look upper left, bright star next to m64. Super annoying. I use APP for processing. Thanks in advance any help is appreciated

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    Default Re: Bright stars have different colors

    Someone knowledgeable will comment on the colors. I just want to say that the galaxy looks great!
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    Default Re: Bright stars have different colors

    If you were shooting with an OSC camera, I would suspect CA. But with filters, it is likely a bit of imprecision in registering the colour masters.

    I had a bit of the same effect in my M101 image from last night. In my case, I blame having to do a meridian flip between the RG and the B series.
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    Default Re: Bright stars have different colors

    Beautiful! Bill
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    Default Re: Bright stars have different colors

    When the stars aren't perfectly shaped or there are focus issues between filters, a particular master (usually red) has bigger stars than the other green or blue. Then what happens is that you get color imperfections that are noticible on the bigger stars because they are brighter. There isn't anything you can really do about the focus after the fact but what I would do is go through your subs and be brutal in eliminating bad subs. Once you've done that, restack each filter and then check the star size of the R, G, B--actually blow them up and look at them side by side. If one is bigger than the other (again, usually red), then you could try some star shaping by decreasing star size through a mask. In Pixinsight, I've had some limited success using selective Morphologic Transformation on the red filter and then combining after.
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    Default

    Quote Originally Posted by s24man View Post
    When the stars aren't perfectly shaped or there are focus issues between filters, a particular master (usually red) has bigger stars than the other green or blue. Then what happens is that you get color imperfections that are noticible on the bigger stars because they are brighter. There isn't anything you can really do about the focus after the fact but what I would do is go through your subs and be brutal in eliminating bad subs. Once you've done that, restack each filter and then check the star size of the R, G, B--actually blow them up and look at them side by side. If one is bigger than the other (again, usually red), then you could try some star shaping by decreasing star size through a mask. In Pixinsight, I've had some limited success using selective Morphologic Transformation on the red filter and then combining after.
    Thank you, I always thought blue and green would bloat more. Can you explain why red does more?

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    Default Re: Bright stars have different colors

    Quote Originally Posted by s24man View Post
    When the stars aren't perfectly shaped or there are focus issues between filters, a particular master (usually red) has bigger stars than the other green or blue. Then what happens is that you get color imperfections that are noticible on the bigger stars because they are brighter. There isn't anything you can really do about the focus after the fact but what I would do is go through your subs and be brutal in eliminating bad subs. Once you've done that, restack each filter and then check the star size of the R, G, B--actually blow them up and look at them side by side. If one is bigger than the other (again, usually red), then you could try some star shaping by decreasing star size through a mask. In Pixinsight, I've had some limited success using selective Morphologic Transformation on the red filter and then combining after.
    Thanks for the explanation and suggestions Stuart. I have this problem a lot with my ES ED102 and will try your suggestions.

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    Default Re: Bright stars have different colors

    It looks though as if the lower left side of the halos is red and the upper right side is green throughout the image so no filter has a larger footprint than the other. Could the focuser be tilted?

    Or like Kathy said, maybe there is something wrong with the color masters perhaps a relative shift. But if they were shifted the spread of the smaller stars would have the same shift size as the larger ones but they are obviously smaller.
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    Default

    Quote Originally Posted by CamelHat View Post
    It looks though as if the lower left side of the halos is red and the upper right side is green throughout the image so no filter has a larger footprint than the other. Could the focuser be tilted?

    Or like Kathy said, maybe there is something wrong with the color masters perhaps a relative shift. But if they were shifted the spread of the smaller stars would have the same shift size as the larger ones but they are obviously smaller.
    Well, I suppose its trial and error. Gonna suck it up and attempt to figure it, or fringe kill it in Startools if worse comes to worse. Just frustrated is all. Focuser tilt, possibly.

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    Default Re: Bright stars have different colors

    Quote Originally Posted by STEVE333 View Post
    Thanks for the explanation and suggestions Stuart. I have this problem a lot with my ES ED102 and will try your suggestions.

    Steve
    Mine just bloats more. That's what I meant.
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