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Re: Red fringing on stars

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  • Wade Van Arsdale
    Hi Wayne, That makes sense, especially since I see varying degrees of this effect depending on what filter is used. What worries me about this is what if it
    Message 1 of 12 , Nov 4, 2006
      Hi Wayne,
      That makes sense, especially since I see varying degrees of this
      effect depending on what filter is used. What worries me about
      this is what if it is inherent red shift from the RGB pixel overlay
      itself in the detector? That's going to be a tough one to solve.
      What stumps me here is that effect is a recognized characteristic
      to some extent in one-shot color cams if I understand the
      documentation correctly, and that is one thing the supplied UV/IR
      cutoff filter is supposed to fix, but in my case, its not fixing
      it. Pretty strange. I may have to experiment with several
      different filters and just go with the cutoff filter that reduces
      this the best, then rely on Photoshop tricks to solve it the rest of
      the way.

      Thanks,
      Wade

      /////////
      --- In tmboptical@yahoogroups.com, Wayne G <fomalhaut@...> wrote:
      >
      > Tube Tim wrote:
      > > The question being, is this
      > > the objective or the filters? From star tests of my scopes, it's
      > > obviously the filter.
      > >
      >
      > WG: Guys, it HAS to be in the filter (or detector): the star
      images
      > are superb in the photos other than a very slight red fringe---
      what
      > could affect the red in the objective without throwing the *rest*
      of the
      > spurious disc out of whack, too?
      >
      > WayneG
      >
    • Wade Van Arsdale
      Hi Tim, More below. Thanks, Wade ... A: I agree. That is what I always have done when doing LRGB mono imaging. I also tend to refocus anyway about every 30
      Message 2 of 12 , Nov 4, 2006
        Hi Tim,
        More below.

        Thanks,
        Wade

        --- In tmboptical@yahoogroups.com, "Tube Tim" <potentate@...> wrote:
        >
        > >--- In tmboptical@yahoogroups.com, "Wade Van Arsdale" <uwpf23@
        > > wrote:
        >...."In other words, set focus to where all channels are equally
        > close to focus".
        A: I agree. That is what I always have done when doing LRGB mono
        imaging. I also tend to refocus anyway about every 30 minutes, as
        there seems to be enough temperature flex in the hardware that it
        seems to help to do this. I do think many times from what I've
        seen, changing filters results in slightly changing focus
        requirements, even in filters touted to be parfocal.


        > It is possible the TMB 152 is so sharp it's showing problems in the
        > CCD that the SCT can't. It's as if the SCT is 'blurring' the
        > difficulty in the CCD. Or the depth of focus is deeper on the SCT.

        A: I think this is a distinct possibility. There is no doubt the
        overall star bloat is going to be greater on the typical SCT than on
        the typical TMB triplet APO. If ALL channels are bloated on the
        SCT, this may be overlaying the red fringe in the stars with the
        other two channels and masking it. This may not be the ONLY thing
        going on here, but I'll bet it is ONE of the things going on that
        causes this effect to show up.

        > Personally, I think the mono-CCD is the way to go. If your pressed
        > for time, have CCD Commander man the scope for the night.

        A: The time problems also are worsened by horizon obstructions at
        my location. I have about a three hour window any given night to
        shoot an object. That makes it harder to get a finished product.
        Using the one-shot helps offset this, but I'd rather have a really
        good shot every now and then than more shots but of inferior quality.
        I may have to just suck it up and go back to LRGB. If that's the
        biggest decision I have to make for awhile, I'm a lucky man for sure.

        > >
        >
        > This sounds very promising. I was going to suggest sending me a
        small
        > FIT file of the RAW data and I'd look with AIP4WIN. Only trouble
        is I
        > am not sure if AIP4WIN handles the ST2k raw files, but I gotta
        believe
        > it does.

        A: I'll send you one offlist Tim. Thanks for looking.

        Cheers,
        Wade
      • Wade Van Arsdale
        Regarding the thread on red star fringing, here s the latest update tonight. A fellow imager put me onto this Photoshop plug-in which appears to work very
        Message 3 of 12 , Nov 4, 2006
          Regarding the thread on red star fringing, here's the latest update
          tonight. A fellow imager put me onto this Photoshop plug-in which
          appears to work very well in reducing the fringing. He sees the same
          thing with his SX color camera:
          http://actions.home.att.net/Astronomy_Tools.html

          Here is how this worked to reduce the red-fringing to very
          acceptable levels:
          1) Split the finished final full color .fits file into its
          individual RBG channels in Maxim. Save these RGB files.
          2) Open only the Red channel file in Photoshop.
          3) Use the Lasso tool in Photoshop to draw boundaries around all
          the galxies in the FOV (or whatever is applicable in your own image).
          4) Choose the "Inverse" selection from the Select menuitem. This
          will allow the plug-in to run on everything BUT the galaxies
          themselves.
          5) Run the Astronomy Tools/*MAKE STARS SMALLER* option in the
          Action Palette of Photoshop (just one iteration was all that was
          needed for this image). Run this *ONLY* on the Red channel file.
          Leave the B and G images alone.
          6) Save the edited Red file.
          7) Open the individual RGB channel files in Maxim.
          8) Perform an RGB Combine in Maxim. (The Align portion may
          fail if you run several iterations of "Make Stars Smaller").
          9) Apply light iterations of Curves and very small amount of
          Unsharp Mask and color balancing in Photoshop to finish it up.

          Here's the link again for the image in question:
          http://www.compubuild.com/astro/ngc7331.htm

          The image on the left of the above page is the reprocessed one
          showing much better control of the red fringing we've been talking
          about. The image on the right side is the original with the fringing
          problems.

          This might be an acceptable way to fix this problem if no other
          solution can be found in the hardware.

          Thanks everyone for your help and input. If I can find a filter
          solution or other hardware solution that works with the one-shot
          color camera, I'll post here as soon as I have something useful.

          Cheers,
          Wade

          /////////////


          --- In tmboptical@yahoogroups.com, "Wade Van Arsdale" <uwpf23@...>
          wrote:
          >
          > Hi Tim,
          > More below.
          >
          > Thanks,
          > Wade
          >
          > --- In tmboptical@yahoogroups.com, "Tube Tim" <potentate@> wrote:
          > >
          > > >--- In tmboptical@yahoogroups.com, "Wade Van Arsdale" <uwpf23@
          > > > wrote:
          > >...."In other words, set focus to where all channels are equally
          > > close to focus".
          > A: I agree. That is what I always have done when doing LRGB mono
          > imaging. I also tend to refocus anyway about every 30 minutes, as
          > there seems to be enough temperature flex in the hardware that it
          > seems to help to do this. I do think many times from what I've
          > seen, changing filters results in slightly changing focus
          > requirements, even in filters touted to be parfocal.
          >
          >
          > > It is possible the TMB 152 is so sharp it's showing problems in
          the
          > > CCD that the SCT can't. It's as if the SCT is 'blurring' the
          > > difficulty in the CCD. Or the depth of focus is deeper on the
          SCT.
          >
          > A: I think this is a distinct possibility. There is no doubt the
          > overall star bloat is going to be greater on the typical SCT than
          on
          > the typical TMB triplet APO. If ALL channels are bloated on the
          > SCT, this may be overlaying the red fringe in the stars with the
          > other two channels and masking it. This may not be the ONLY thing
          > going on here, but I'll bet it is ONE of the things going on that
          > causes this effect to show up.
          >
          > > Personally, I think the mono-CCD is the way to go. If your
          pressed
          > > for time, have CCD Commander man the scope for the night.
          >
          > A: The time problems also are worsened by horizon obstructions at
          > my location. I have about a three hour window any given night to
          > shoot an object. That makes it harder to get a finished product.
          > Using the one-shot helps offset this, but I'd rather have a really
          > good shot every now and then than more shots but of inferior
          quality.
          > I may have to just suck it up and go back to LRGB. If that's the
          > biggest decision I have to make for awhile, I'm a lucky man for
          sure.
          >
          > > >
          > >
          > > This sounds very promising. I was going to suggest sending me a
          > small
          > > FIT file of the RAW data and I'd look with AIP4WIN. Only
          trouble
          > is I
          > > am not sure if AIP4WIN handles the ST2k raw files, but I gotta
          > believe
          > > it does.
          >
          > A: I'll send you one offlist Tim. Thanks for looking.
          >
          > Cheers,
          > Wade
          >
        • Wayne G
          ... WG: Wade, I don t pretend to be an expert on this stuff, but I wonder if it could be a bit of diffusion going through whatever filter(s) are handling the
          Message 4 of 12 , Nov 5, 2006
            Wade Van Arsdale wrote:
            > Hi Wayne,
            > That makes sense, especially since I see varying degrees of this
            > effect depending on what filter is used. What worries me about
            > this is what if it is inherent red shift from the RGB pixel overlay
            > itself in the detector? That's going to be a tough one to solve.
            > What stumps me here is that effect is a recognized characteristic
            > to some extent in one-shot color cams if I understand the
            > documentation correctly, and that is one thing the supplied UV/IR
            > cutoff filter is supposed to fix, but in my case, its not fixing
            > it. Pretty strange. I may have to experiment with several
            > different filters and just go with the cutoff filter that reduces
            > this the best, then rely on Photoshop tricks to solve it the rest of
            > the way.
            >

            WG: Wade, I don't pretend to be an expert on this stuff, but I wonder
            if it could be a bit of diffusion going through whatever filter(s) are
            handling the red. Or just a bit of bleeding/ leakage at the detector?

            That said, Wade, I gotta tell you in all honesty, I am a photographer
            going back to the mid-1960's--- I cut my teeth on large format Speed
            Graphic in my father's darkroom in the basement (he was a Navy
            photographer in WWII). I am a very critical person when it comes to
            imagery.

            That said, I have to tell you that you take a *mean* picture Wade and
            had you not complained about the little teeny red fringes, I wouldn't
            have thought much about it--- there aren't many pictures that I don't
            see some kind of fringe or geometric distortion for one reason for
            another, if you don't look hard enough.

            You are dealing with a very complex process that *begins* with an all
            dioptric imager (all glass lens). Pretty tall order.

            Sometimes I think you digital astro guys are just too hard on yourselves
            and beat yourselves up! Too much competition for my blood--- no one's
            making a living doing this; it is just a hobby!

            Maybe excruciate if you must over trying to perfect your pictures, but I
            say, "Relax and ENJOY the hobby a bit, too!" Sometimes the more you
            pour into a hobby the harder it is to be satisfied with it!

            But there IS an algorithm which REDUCES the diameter of star images to
            sharpen them up--- don't remember the name--- it, or a cousin of it
            might ameliorate your symptoms w/o chopping a leg off. Personally, I
            LIKE the idea of the one-shot cameras! If I every get into it big time,
            I think I will buy a full sensor CMOS 35mm camera to do it with.

            Just my 2ยข

            WayneG
          • Wade Van Arsdale
            I have another probable solution (from Tim) for the red fringing problem with color one-shot cameras: AIP4WIN for the RBG convert of the raws. Tim ran this on
            Message 5 of 12 , Nov 5, 2006
              I have another probable solution (from Tim) for the red fringing
              problem with color one-shot cameras: AIP4WIN for the RBG convert of
              the raws. Tim ran this on my test raw frame and it fixed it
              completely. So evidently it is the DeBayering process itself in
              the software that is the source of this. That suprises me, but not
              completely, knowing that the DeBayering of one-shot color frames is
              done through different algorithms in different softwares.

              So it looks like I have two very effective ways to deal with the
              red-fringing on bright stars:
              1) Astronomy Tools for Photoshop/"Make Stars Smaller" plug-in run on
              the Red channel.
              2) Instead of #1 above, do an RBG convert on the raws in AIP4WIN
              instead of Maxim to get a different DeBayering process.

              Both methods seem to be solid ways of working around this problem.
              Thanks Tim and everyone for helping me work this out. Now I can get
              back to imaging and quit wondering if something is wrong with my
              gear.

              Cheers,
              Wade

              //////////

              --- In tmboptical@yahoogroups.com, "Wade Van Arsdale" <uwpf23@...>
              wrote:
              >
              > Regarding the thread on red star fringing, here's the latest update
              > tonight. A fellow imager put me onto this Photoshop plug-in which
              > appears to work very well in reducing the fringing. He sees the
              same
              > thing with his SX color camera:
              > http://actions.home.att.net/Astronomy_Tools.html
              >
              > Here is how this worked to reduce the red-fringing to very
              > acceptable levels:
              > 1) Split the finished final full color .fits file into its
              > individual RBG channels in Maxim. Save these RGB files.
              > 2) Open only the Red channel file in Photoshop.
              > 3) Use the Lasso tool in Photoshop to draw boundaries around all
              > the galxies in the FOV (or whatever is applicable in your own
              image).
              > 4) Choose the "Inverse" selection from the Select menuitem. This
              > will allow the plug-in to run on everything BUT the galaxies
              > themselves.
              > 5) Run the Astronomy Tools/*MAKE STARS SMALLER* option in the
              > Action Palette of Photoshop (just one iteration was all that was
              > needed for this image). Run this *ONLY* on the Red channel file.
              > Leave the B and G images alone.
              > 6) Save the edited Red file.
              > 7) Open the individual RGB channel files in Maxim.
              > 8) Perform an RGB Combine in Maxim. (The Align portion may
              > fail if you run several iterations of "Make Stars Smaller").
              > 9) Apply light iterations of Curves and very small amount of
              > Unsharp Mask and color balancing in Photoshop to finish it up.
              >
              > Here's the link again for the image in question:
              > http://www.compubuild.com/astro/ngc7331.htm
              >
              > The image on the left of the above page is the reprocessed one
              > showing much better control of the red fringing we've been talking
              > about. The image on the right side is the original with the
              fringing
              > problems.
              >
              > This might be an acceptable way to fix this problem if no other
              > solution can be found in the hardware.
              >
              > Thanks everyone for your help and input. If I can find a filter
              > solution or other hardware solution that works with the one-shot
              > color camera, I'll post here as soon as I have something useful.
              >
              > Cheers,
              > Wade
              >
              > /////////////
              >
              >
              > --- In tmboptical@yahoogroups.com, "Wade Van Arsdale" <uwpf23@>
              > wrote:
              > >
              > > Hi Tim,
              > > More below.
              > >
              > > Thanks,
              > > Wade
              > >
              > > --- In tmboptical@yahoogroups.com, "Tube Tim" <potentate@> wrote:
              > > >
              > > > >--- In tmboptical@yahoogroups.com, "Wade Van Arsdale" <uwpf23@
              > > > > wrote:
              > > >...."In other words, set focus to where all channels are equally
              > > > close to focus".
              > > A: I agree. That is what I always have done when doing LRGB mono
              > > imaging. I also tend to refocus anyway about every 30 minutes,
              as
              > > there seems to be enough temperature flex in the hardware that it
              > > seems to help to do this. I do think many times from what I've
              > > seen, changing filters results in slightly changing focus
              > > requirements, even in filters touted to be parfocal.
              > >
              > >
              > > > It is possible the TMB 152 is so sharp it's showing problems
              in
              > the
              > > > CCD that the SCT can't. It's as if the SCT is 'blurring' the
              > > > difficulty in the CCD. Or the depth of focus is deeper on the
              > SCT.
              > >
              > > A: I think this is a distinct possibility. There is no doubt
              the
              > > overall star bloat is going to be greater on the typical SCT
              than
              > on
              > > the typical TMB triplet APO. If ALL channels are bloated on the
              > > SCT, this may be overlaying the red fringe in the stars with the
              > > other two channels and masking it. This may not be the ONLY thing
              > > going on here, but I'll bet it is ONE of the things going on that
              > > causes this effect to show up.
              > >
              > > > Personally, I think the mono-CCD is the way to go. If your
              > pressed
              > > > for time, have CCD Commander man the scope for the night.
              > >
              > > A: The time problems also are worsened by horizon obstructions
              at
              > > my location. I have about a three hour window any given night to
              > > shoot an object. That makes it harder to get a finished product.
              > > Using the one-shot helps offset this, but I'd rather have a
              really
              > > good shot every now and then than more shots but of inferior
              > quality.
              > > I may have to just suck it up and go back to LRGB. If that's the
              > > biggest decision I have to make for awhile, I'm a lucky man for
              > sure.
              > >
              > > > >
              > > >
              > > > This sounds very promising. I was going to suggest sending me
              a
              > > small
              > > > FIT file of the RAW data and I'd look with AIP4WIN. Only
              > trouble
              > > is I
              > > > am not sure if AIP4WIN handles the ST2k raw files, but I gotta
              > > believe
              > > > it does.
              > >
              > > A: I'll send you one offlist Tim. Thanks for looking.
              > >
              > > Cheers,
              > > Wade
              > >
              >
            • Wade Van Arsdale
              Hi Wayne, More below. Thanks, Wade ... Wade....
              Message 6 of 12 , Nov 5, 2006
                Hi Wayne,
                More below.

                Thanks,
                Wade

                >...That said, I have to tell you that you take a *mean* picture
                Wade....<<<
                A: Thanks, Wayne. You're being pretty generous there. I can't
                hang with the "big boys", but I *do* try my best, and part of the
                fun of it for me is pushing myself to learn as much as possible
                about it. I don't fret too much though, because this is a fun
                diversion for me from my "real" job, which can be pretty crappy
                and stressful a lot of the time. If you saw my images from a year
                ago, you'd probably agree the learning process has made my images
                a lot more presentable.

                > You are dealing with a very complex process that *begins* with an
                all dioptric imager (all glass lens). Pretty tall order.,,,<<<

                A: That's the truth, as I continue to find out when this new stuff
                comes up.


                >....Sometimes I think you digital astro guys are just too hard on
                yourselves and beat yourselves up! Too much competition for my
                blood---no one's making a living doing this it is just a hobby..<<<!

                A: Ain't it the truth! Actually though, I never feel like I'm
                in some kind of competition with anybody else with this stuff. I
                save the friendly competition for the golf course with my buddies.
                This imaging stuff is just for fun (at least for me). My only goal
                with my images is my own enjoyment, and if someone else derives
                some pleasure out of looking at them too, then that is the icing
                on the cake for me and gives me even more enjoyment from doing it.
                I just try to always learn more as I go and do the best I know how
                to do...that's part of the fun for me too with imaging.

                > Maybe excruciate if you must over trying to perfect your pictures,
                but I say, "Relax and ENJOY the hobby a bit, too!".

                A: Good advice. I always take some time out to just get some
                saddle time in at the eyepiece and do visual astronomy only. That
                is pretty peaceful and rewarding time and is priceless to me. I do
                wish more imagers would always find time for some visual enjoyment
                of the hobby as well. It will pay you back tenfold for your time
                investment in it.

                >>>...But there IS an algorithm which REDUCES the diameter of star
                images to sharpen them up--- don't remember the name--- it, or a
                cousin of it might ameliorate your symptoms....<<<<<

                A: I was fortunate enough to have a fellow imager on another group
                post about this. It may be the same thing you are thinking about.
                It's an applet called "Make Stars Smaller" within a Photoshop plugin
                called "Astronomy Tools for Photoshop". His solution was what I
                posted about here earlier, and it really works well. It has
                basically solved this for me, so I went ahead and passed the info on
                here and on one other group. Tim here has helped a bunch also and
                I appreciate them (and you) helping me out greatly. Probably saved
                me many hours, and that WOULD have gotten pretty frustrating if I
                couldn't solve it.

                >>>..Personally, I LIKE the idea of the one-shot cameras!<<<

                A: What really intrigued me about this concept is the time-savings
                from it, as my time is so limited by job requirements, and my
                location's horizon obstructions also contribute. It just seems that
                I can get all the way to a completed project and get an image out
                there better with the one-shot color, and it is a lot of fun working
                with this type of camera because it is so simple on the processing
                end compared to LRGB processing (well, at least it WAS simple before
                all this new stuff came up!!).

                The TMB's have such sharp focus in their optics, they make up for
                the slight loss of image sharpness that can occur with the one-
                shot cameras due to the RGB pixel matrix overlay, at least compared
                to my SCT's that I used to use for all my imaging. Now that I have
                a couple of good ways to control the slight out-of-focus in the red
                channel, I think I can get results that are very close to
                traditional LRGB mono cameras. I'll never beat the results from
                that type of camera, but I think I'll get close. Also, I can knock
                out a good image in 2-4 hours of exposure time typically with the
                one-shot, which simplifies things for me.

                I still do LRGB mono imaging too with this same camera's "brother"
                (ST2000XM) at times, when it's something brighter that requires less
                exposure time, but I just seem to get all the way to completion
                better on the DSO's with the one-shot. I count myself lucky that I
                have the option to go either way with it.

                Take care Wayne, and I always enjoy reading your posts. Always
                some good advice to be had from you.

                Cheers,
                Wade
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