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Re: Silly!? LP Filter Question

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  • Eddie Guscott
    Thank you Don Just when I think this hobby is getting a little bit easier, along comes another set of problems. Now, we just need some clear skies.... Eddie
    Message 1 of 10 , Jan 1, 2005
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      Thank you Don

      Just when I think this hobby is getting a little bit easier, along
      comes another set of problems.

      Now, we just need some clear skies....

      Eddie Guscott


      --- In ccd-newastro@yahoogroups.com, "Don Goldman"
      <donclearview@y...> wrote:
      >
      >
      > First, I did make a mistake that Peter caught. Embarrassing
      because
      > reading spectral plots is my expertise <g>. The IDAS LPS filters
      DO
      > block the NIR and will help with nearby incandescent lights.
      > Therefore, your Clear (NIR unblocked) filter will be "blocked" by
      the
      > LPS. Thus you will lose 40% of your total signal because your LPS
      > blocks the NIR on a camera like the ST10, and you will lose
      another
      > amount because it is taking out portions of the visible spectrum
      for
      > the Hg, Na and skyglow lines.
      >
      > Second, the LPS filter lets most of the H-a emission through so
      you
      > won't see much of a difference with or w/o the LPS for H-a.
      >
      > Third, if you determine that you need to use the LPS and take the
      > light hit, you should use it for all the filters including the
      > luminance. The same light pollution that will come into your blue
      > filter will come in to your lumiance filter, as well.
      >
      > Ron's first book, and i'm sure the new one talks about processing
      > techniques to remove gradients. Maxim4.0 and other programs like
      MIRA
      > have methods to flatten backgrounds and remove gradients, and Ron
      > provides a plug-in to do the same in Maxim. I take out gradients
      in
      > my RGB using Photoshop if the object is small, like a galaxy in
      the
      > middle of a large star-field. I duplicate the layer, use the dust
      > and scratches filter to remove most of the stars, clone out the
      > galaxy in the direction of the gradient, do a large scale Gaussian
      > blur and then change the blending mode to difference. I also raise
      > the black point in the original layer to about 17 to avoid
      clipping.
      > Sounds complicated, but is really quite easy. Works well and is
      quick
      > if you have enough of a star field. Won't work for something like
      > M101 taking up the whole field or a nebula that fills up the
      frame.
      > Hope that helped.
      >
      > Don Goldman
      > www.astrodon.com
      >
      >
      >
      > > Thanks Don for the explanation.
      > >
      > > I am basically a "lazy" imager, and prefer as few adustments
      etc..
      > > as possible whilst imaging.
      > >
      > > I have previously imaged RGB with the IDAS LP filter and with no
      LP
      > > filter for the Lum or Ha.
      > >
      > > This, however, involved separate flat fields for the RGB and Lum
      > > exposures as I had physically removed the camera from the scope
      to
      > > remove the LP filter, thus changing the position of my "dust
      > > motes" !!!
      > >
      > > I'm wondering if the inclusion of a "filter slider" in the
      optical
      > > path somewhere would help - just slide the LP filter into the
      path
      > > for RGB imaging and slide it out again for Lum and Ha imaging.
      > >
      > > Either that, or do as Mark suggested, just process out the light
      > > pollution. Anyone know of any decent tutorials for removing
      > > gradients???
      > >
      > > Eddie Guscott
      > >
      > > --- In ccd-newastro@yahoogroups.com, "Don Goldman"
      > > <donclearview@y...> wrote:
      > > >
      > > > Not silly at all. This has been discussed many times and needs
      to
      > > be
      > > > brought up from time to time. I have a good discussion on my
      web
      > > > site at:
      > > >
      > > > http://www.astrodon.com/LPSFilters.html
      > > >
      > > > Peter is correct. It depends upon the type of light pollution
      > that
      > > > you have. The sodium and mercury street lights are minimized
      with
      > > the
      > > > Hutech LPS, but it doesn't help much with incandescent lights,
      > > like
      > > > your neighbor's flood lamps and most home outdoor lighting.
      If
      > > you
      > > > use the most current (P2) IDAS LPS, you'll lose about 40% of
      you
      > > RGB
      > > > or NIR blocked signal based upon the analysis in my RGB Weight
      > > > Calculator. I tend toward Mark's position. I can process out
      > most
      > > of
      > > > the effects and would rather not lose the signal. Two things
      to
      > > > note. First, it will change your G2V color combine weights, so
      > > either
      > > > shoot a G2V star and recompute with the LPS, or use my
      Calculator
      > > > software. Second, incadescent bulbs have alot of NIR that the
      > IDAS
      > > > filter does not block. So, you may be better off NOT using a
      > Clear
      > > > (no NIR blocking) filter and opt for a Luminance (NIR blocked)
      > > filter
      > > > instead. The clear filter does capture more light, but in a
      > light
      > > > polluted areas, alot of that NIR will be contaminated from the
      > > > incandescent lights nearby, so you will be adding more noise.
      Of
      > > > course, then there's the other discussion as to whether you
      > should
      > > be
      > > > mixing in ANY NIR in your luminance with the RGB, but that's a
      > > > discussion for another day.
      > > >
      > > > Don Goldman
      > > > www.astrodon.com
      > > >
      > > >
      > > > --- In ccd-newastro@yahoogroups.com, "Eddie Guscott"
      > > > <eddie.guscott@b...> wrote:
      > > > >
      > > > > I know there are a lot of knowlegeable folks here, so I
      thought
      > > I'd
      > > > > ask my silly question.
      > > > >
      > > > > Is there a downside to installing a LP filter between
      > > camera/filter
      > > > > wheel and scope and then leaving it there. This would mean
      > > imaging
      > > > > not just RGB through the LP filter but clear and Ha as well.
      > > > >
      > > > > I normally take the LP filter off for clear (Lum) and Ha
      > imaging.
      > > > >
      > > > > Eddie Guscott
    • Wayne Cooper
      Cool processing technique. i ve got to look this over more thoroughly. Thanks for the added info. Happy New Year, Wayne http://www.wayne-cooper.com ... because
      Message 2 of 10 , Jan 1, 2005
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        Cool processing technique. i've got to look this over more
        thoroughly. Thanks for the added info. Happy New Year, Wayne
        http://www.wayne-cooper.com


        --- In ccd-newastro@yahoogroups.com, "Don Goldman"
        <donclearview@y...> wrote:
        >
        >
        > First, I did make a mistake that Peter caught. Embarrassing
        because
        > reading spectral plots is my expertise <g>. The IDAS LPS filters DO
        > block the NIR and will help with nearby incandescent lights.
        > Therefore, your Clear (NIR unblocked) filter will be "blocked" by
        the
        > LPS. Thus you will lose 40% of your total signal because your LPS
        > blocks the NIR on a camera like the ST10, and you will lose another
        > amount because it is taking out portions of the visible spectrum
        for
        > the Hg, Na and skyglow lines.
        >
        > Second, the LPS filter lets most of the H-a emission through so you
        > won't see much of a difference with or w/o the LPS for H-a.
        >
        > Third, if you determine that you need to use the LPS and take the
        > light hit, you should use it for all the filters including the
        > luminance. The same light pollution that will come into your blue
        > filter will come in to your lumiance filter, as well.
        >
        > Ron's first book, and i'm sure the new one talks about processing
        > techniques to remove gradients. Maxim4.0 and other programs like
        MIRA
        > have methods to flatten backgrounds and remove gradients, and Ron
        > provides a plug-in to do the same in Maxim. I take out gradients
        in
        > my RGB using Photoshop if the object is small, like a galaxy in the
        > middle of a large star-field. I duplicate the layer, use the dust
        > and scratches filter to remove most of the stars, clone out the
        > galaxy in the direction of the gradient, do a large scale Gaussian
        > blur and then change the blending mode to difference. I also raise
        > the black point in the original layer to about 17 to avoid
        clipping.
        > Sounds complicated, but is really quite easy. Works well and is
        quick
        > if you have enough of a star field. Won't work for something like
        > M101 taking up the whole field or a nebula that fills up the frame.
        > Hope that helped.
        >
        > Don Goldman
        > www.astrodon.com
        >
        >
        >
        > > Thanks Don for the explanation.
        > >
        > > I am basically a "lazy" imager, and prefer as few adustments
        etc..
        > > as possible whilst imaging.
        > >
        > > I have previously imaged RGB with the IDAS LP filter and with no
        LP
        > > filter for the Lum or Ha.
        > >
        > > This, however, involved separate flat fields for the RGB and Lum
        > > exposures as I had physically removed the camera from the scope
        to
        > > remove the LP filter, thus changing the position of my "dust
        > > motes" !!!
        > >
        > > I'm wondering if the inclusion of a "filter slider" in the
        optical
        > > path somewhere would help - just slide the LP filter into the
        path
        > > for RGB imaging and slide it out again for Lum and Ha imaging.
        > >
        > > Either that, or do as Mark suggested, just process out the light
        > > pollution. Anyone know of any decent tutorials for removing
        > > gradients???
        > >
        > > Eddie Guscott
        > >
        > > --- In ccd-newastro@yahoogroups.com, "Don Goldman"
        > > <donclearview@y...> wrote:
        > > >
        > > > Not silly at all. This has been discussed many times and needs
        to
        > > be
        > > > brought up from time to time. I have a good discussion on my
        web
        > > > site at:
        > > >
        > > > http://www.astrodon.com/LPSFilters.html
        > > >
        > > > Peter is correct. It depends upon the type of light pollution
        > that
        > > > you have. The sodium and mercury street lights are minimized
        with
        > > the
        > > > Hutech LPS, but it doesn't help much with incandescent lights,
        > > like
        > > > your neighbor's flood lamps and most home outdoor lighting. If
        > > you
        > > > use the most current (P2) IDAS LPS, you'll lose about 40% of
        you
        > > RGB
        > > > or NIR blocked signal based upon the analysis in my RGB Weight
        > > > Calculator. I tend toward Mark's position. I can process out
        > most
        > > of
        > > > the effects and would rather not lose the signal. Two things
        to
        > > > note. First, it will change your G2V color combine weights, so
        > > either
        > > > shoot a G2V star and recompute with the LPS, or use my
        Calculator
        > > > software. Second, incadescent bulbs have alot of NIR that the
        > IDAS
        > > > filter does not block. So, you may be better off NOT using a
        > Clear
        > > > (no NIR blocking) filter and opt for a Luminance (NIR blocked)
        > > filter
        > > > instead. The clear filter does capture more light, but in a
        > light
        > > > polluted areas, alot of that NIR will be contaminated from the
        > > > incandescent lights nearby, so you will be adding more noise.
        Of
        > > > course, then there's the other discussion as to whether you
        > should
        > > be
        > > > mixing in ANY NIR in your luminance with the RGB, but that's a
        > > > discussion for another day.
        > > >
        > > > Don Goldman
        > > > www.astrodon.com
        > > >
        > > >
        > > > --- In ccd-newastro@yahoogroups.com, "Eddie Guscott"
        > > > <eddie.guscott@b...> wrote:
        > > > >
        > > > > I know there are a lot of knowlegeable folks here, so I
        thought
        > > I'd
        > > > > ask my silly question.
        > > > >
        > > > > Is there a downside to installing a LP filter between
        > > camera/filter
        > > > > wheel and scope and then leaving it there. This would mean
        > > imaging
        > > > > not just RGB through the LP filter but clear and Ha as well.
        > > > >
        > > > > I normally take the LP filter off for clear (Lum) and Ha
        > imaging.
        > > > >
        > > > > Eddie Guscott
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