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Re: Choice of SBIG for Takahashi TOA-130 in light-polluted city skies?

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  • htrott
    Hi Ron: Thanks for your quick reply, and also Jon s tip to look at Daniel Perry s site (I have before, and his results with the TOA-130 near LA are an
    Message 1 of 23 , Jun 3, 2007
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      Hi Ron:

      Thanks for your quick reply, and also Jon's tip to look at
      Daniel Perry's site (I have before, and his results with
      the TOA-130 near LA are an inspiration!).

      I hope I can squeeze in a few follow-up questions, to help
      me nail this down.

      What about the ST-8, down slightly in resolution (to 1.85"/pixel at
      the native fratio of the TOA-130), and FOV, from the ST-10, but also
      down quite a bit in price? From what I can understand from the SBIG
      specs, the ST-8 does not have the microlenses that you pointed to as a
      bit of problem with the ST-10.

      In terms of dSLR's, I'm a little concerned about how difficult
      it will be to modify the camera, in order to remove the IR block
      and RGB filters. How much of a challenge is that (for someone
      with little equipment or experience)? I'm also unclear about just
      how much advantage one gets from the cooling of a dedicated imager,
      versus simply having the dark frames for a dSLR.

      In the comparison between the NABG and ABG cameras, does one just
      take the ratio of QE, squared, to determine the increased exposure
      time? I'm also not sure how to factor in the effects of light
      pollution, with a given limiting visual magnitude as input, though
      perhaps I'm trying to be overly theoretical at this point!

      Thanks for any additional input.

      Cheers,
      Howard.

      --- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@...> wrote:
      >
      > I think your analysis is on the mark - in light polluted skies, the
      NABG
      > cameras are usually the better choice.
      >
      > The ST-10 is pretty much my first choice for refractors 6" and smaller.
      > It has a good combination of pixel size and sensitivity. You do get
      some
      > minor reflections from the microlenses that put short vertical
      spikes on
      > the stars - SBIG's CCDOPS program has a utility for cleaning this up,
      > but it's not user friendly.
      >
      > If money is an issue, then the new Canon Rebel xti makes a very good
      > starter camera for most small refractors until you are ready to get a
      > high-end camera.
      >
      > Ron Wodaski
    • Yahoo - Wodaski
      See below. Ron Wodaski ... I ve imaged with 4, 5, and 6-inch refractors with both the ST-10 and the ST-8. It makes a surprisingly large difference to get the
      Message 2 of 23 , Jun 3, 2007
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        See below.

        Ron Wodaski

        htrott wrote:
        > Hi Ron:
        >
        > Thanks for your quick reply, and also Jon's tip to look at
        > Daniel Perry's site (I have before, and his results with
        > the TOA-130 near LA are an inspiration!).
        >
        > I hope I can squeeze in a few follow-up questions, to help
        > me nail this down.
        >
        > What about the ST-8, down slightly in resolution (to 1.85"/pixel at
        > the native fratio of the TOA-130), and FOV, from the ST-10, but also
        > down quite a bit in price? From what I can understand from the SBIG
        > specs, the ST-8 does not have the microlenses that you pointed to as a
        > bit of problem with the ST-10.
        >
        I've imaged with 4, 5, and 6-inch refractors with both the ST-10 and the
        ST-8. It makes a surprisingly large difference to get the extra
        resolution. Knowing your interest in galaxies, I didn't mention the ST-8
        for this reason. I wasn't convinced it would satisfy you.
        > In terms of dSLR's, I'm a little concerned about how difficult
        > it will be to modify the camera, in order to remove the IR block
        > and RGB filters. How much of a challenge is that (for someone
        > with little equipment or experience)?
        On a camera like the Rebel xti, it's pretty challenging. I'm no slouch,
        and I wouldn't do it. In fact, the only imaging I've done with the xti
        (on an E180) was without the modification The results were OK, but red
        was obviously lighter than it should be. Still, it was fun and I have
        several neighbors who enjoy imaging both with and without the
        modification. And if you don't modify, it's easy and fun to use the xti
        as a terrestrial camera as well (love mine for that purpose!).
        > I'm also unclear about just
        > how much advantage one gets from the cooling of a dedicated imager,
        > versus simply having the dark frames for a dSLR.
        >
        The reason I specifically mentioned the xti is that you can take really
        quite nice images without dark frames at all. Very convenient, and the
        results are surprisingly good. But I would encourage you to image that
        way mostly at the faster focal ratios (f/5 or better, or thereabouts -
        f/6 might be OK but haven't tried it).
        > In the comparison between the NABG and ABG cameras, does one just
        > take the ratio of QE, squared, to determine the increased exposure
        > time?
        ABG and NABG cameras have very different characters. The one is limited
        by blooming; the other allows longer exposure times under dark skies.
        It's just not a simple comparison, IMO. I hate dealing with blooms, so I
        would only consider an NAGB in bright skies. Because I can image for
        really long times under dark skies, an ABG can really dig deep without
        blooms (I'm thinking of hour-long sub-exposures).
        > I'm also not sure how to factor in the effects of light
        > pollution, with a given limiting visual magnitude as input, though
        > perhaps I'm trying to be overly theoretical at this point!
        >
        Yeah, it's awfully hard to quantify. I would think that the transition
        to NABG should happen somehwere around mag 4-5 skies, but it really
        varies depending on the source of your pollution (what color
        dominates?), whether you plan to do a lot of narrowband imaging, the
        focal ratio of your scope, the wavelength-dependent QE of your chip, etc.
        > Thanks for any additional input.
        >
        > Cheers,
        > Howard.
        >
        > --- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@...> wrote:
        >
        >> I think your analysis is on the mark - in light polluted skies, the
        >>
        > NABG
        >
        >> cameras are usually the better choice.
        >>
        >> The ST-10 is pretty much my first choice for refractors 6" and smaller.
        >> It has a good combination of pixel size and sensitivity. You do get
        >>
        > some
        >
        >> minor reflections from the microlenses that put short vertical
        >>
        > spikes on
        >
        >> the stars - SBIG's CCDOPS program has a utility for cleaning this up,
        >> but it's not user friendly.
        >>
        >> If money is an issue, then the new Canon Rebel xti makes a very good
        >> starter camera for most small refractors until you are ready to get a
        >> high-end camera.
        >>
        >> Ron Wodaski
        >>
        >
        >
        >
        >
        > Yahoo! Groups Links
        >
        >
        >
        >
      • john walton
        Hi Howard, DSLR modification is quite a challange. The Hutech rangestarting at $1000: http://www.sciencecenter.net/hutech/canon/index.htm Is much more cost
        Message 3 of 23 , Jun 3, 2007
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          Hi Howard,
          DSLR modification is quite a challange.
          The Hutech rangestarting at $1000:

          http://www.sciencecenter.net/hutech/canon/index.htm

          Is much more cost effective, (unless you would enjoy losing tiny,tiny screws.)

          Also:

          http://www.hapg.org/camera%20mods.htm

          starting at $600

          Cheers
          Jon
          ----- Original Message -----
          From: htrott
          To: ccd-newastro@yahoogroups.com
          Sent: Sunday, June 03, 2007 9:25 PM
          Subject: [ccd-newastro] Re: Choice of SBIG for Takahashi TOA-130 in light-polluted city skies?


          Hi Ron:

          Thanks for your quick reply, and also Jon's tip to look at
          Daniel Perry's site (I have before, and his results with
          the TOA-130 near LA are an inspiration!).

          I hope I can squeeze in a few follow-up questions, to help
          me nail this down.

          What about the ST-8, down slightly in resolution (to 1.85"/pixel at
          the native fratio of the TOA-130), and FOV, from the ST-10, but also
          down quite a bit in price? From what I can understand from the SBIG
          specs, the ST-8 does not have the microlenses that you pointed to as a
          bit of problem with the ST-10.

          In terms of dSLR's, I'm a little concerned about how difficult
          it will be to modify the camera, in order to remove the IR block
          and RGB filters. How much of a challenge is that (for someone
          with little equipment or experience)? I'm also unclear about just
          how much advantage one gets from the cooling of a dedicated imager,
          versus simply having the dark frames for a dSLR.

          In the comparison between the NABG and ABG cameras, does one just
          take the ratio of QE, squared, to determine the increased exposure
          time? I'm also not sure how to factor in the effects of light
          pollution, with a given limiting visual magnitude as input, though
          perhaps I'm trying to be overly theoretical at this point!

          Thanks for any additional input.

          Cheers,
          Howard.

          --- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@...> wrote:
          >
          > I think your analysis is on the mark - in light polluted skies, the
          NABG
          > cameras are usually the better choice.
          >
          > The ST-10 is pretty much my first choice for refractors 6" and smaller.
          > It has a good combination of pixel size and sensitivity. You do get
          some
          > minor reflections from the microlenses that put short vertical
          spikes on
          > the stars - SBIG's CCDOPS program has a utility for cleaning this up,
          > but it's not user friendly.
          >
          > If money is an issue, then the new Canon Rebel xti makes a very good
          > starter camera for most small refractors until you are ready to get a
          > high-end camera.
          >
          > Ron Wodaski





          [Non-text portions of this message have been removed]
        • dannysperry
          Hi Howard, Just thought I d throw in another 2 cents... light pollution by itself isn t the biggest problem I face. It s that the light pollution changes from
          Message 4 of 23 , Jun 4, 2007
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            Hi Howard,

            Just thought I'd throw in another 2 cents... light pollution by
            itself isn't the biggest problem I face. It's that the light
            pollution changes from region to region in the sky. This makes it
            nearly impossible to effectively remove the gradients it causes. If
            it was simple vignetting or a straight gradient, I could remove it
            with software without much problem. But because of the local
            pollution I encounter (street lights, neighbors' porch lights) and
            the fact that the amount of pollution changes as I track an object
            throughout the night, the gradients are all over the place.

            If I'm able to restrict imaging to a 2-3 hour window with the scope
            pointing almost straight up, that's when things turn out the best. :)

            I just took a few 20-minute Ha images of M57 the other night (through
            the TOA-130). The Ha filter gets rid of nearly all those darn
            gradients but, of course, my targets are somewhat limited and I DO
            still need to image longer than I would under darker skies. But I'll
            take what I can get. :)

            I'll post the image once I get some more data (another 2-3 hours
            worth, hopefully).

            BTW, if you haven't already ordered them already, I'd recommend the
            TOA-35 flattener and the TOA/FS 2.7" reducer.

            Best,
            Daniel Perry
            http://www.californiastars.net/


            --- In ccd-newastro@yahoogroups.com, "htrott" <trottier@...> wrote:
            >
            > Hi Ron:
            >
            > Thanks for your quick reply, and also Jon's tip to look at
            > Daniel Perry's site (I have before, and his results with
            > the TOA-130 near LA are an inspiration!).
            >
            > I hope I can squeeze in a few follow-up questions, to help
            > me nail this down.
            >
            > What about the ST-8, down slightly in resolution (to 1.85"/pixel at
            > the native fratio of the TOA-130), and FOV, from the ST-10, but also
            > down quite a bit in price? From what I can understand from the SBIG
            > specs, the ST-8 does not have the microlenses that you pointed to
            as a
            > bit of problem with the ST-10.
            >
            > In terms of dSLR's, I'm a little concerned about how difficult
            > it will be to modify the camera, in order to remove the IR block
            > and RGB filters. How much of a challenge is that (for someone
            > with little equipment or experience)? I'm also unclear about just
            > how much advantage one gets from the cooling of a dedicated imager,
            > versus simply having the dark frames for a dSLR.
            >
            > In the comparison between the NABG and ABG cameras, does one just
            > take the ratio of QE, squared, to determine the increased exposure
            > time? I'm also not sure how to factor in the effects of light
            > pollution, with a given limiting visual magnitude as input, though
            > perhaps I'm trying to be overly theoretical at this point!
            >
            > Thanks for any additional input.
            >
            > Cheers,
            > Howard.
            >
            > --- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@> wrote:
            > >
            > > I think your analysis is on the mark - in light polluted skies,
            the
            > NABG
            > > cameras are usually the better choice.
            > >
            > > The ST-10 is pretty much my first choice for refractors 6" and
            smaller.
            > > It has a good combination of pixel size and sensitivity. You do
            get
            > some
            > > minor reflections from the microlenses that put short vertical
            > spikes on
            > > the stars - SBIG's CCDOPS program has a utility for cleaning this
            up,
            > > but it's not user friendly.
            > >
            > > If money is an issue, then the new Canon Rebel xti makes a very
            good
            > > starter camera for most small refractors until you are ready to
            get a
            > > high-end camera.
            > >
            > > Ron Wodaski
            >
          • Yahoo - Wodaski
            I used to image under skies like that. You should look at Russ Croman s gradientXTerminator software - it work within Photoshop to clean up even really messy
            Message 5 of 23 , Jun 5, 2007
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              I used to image under skies like that. You should look at Russ Croman's
              gradientXTerminator software - it work within Photoshop to clean up even
              really messy gradients (which includes subtle gradients from bad flats
              as well as grosser gradients from light pollution).

              See Russ's site at:

              http://www.rc-astro.com/resources/GradientXTerminator/index.html

              Ron Wodaski

              dannysperry wrote:
              > Hi Howard,
              >
              > Just thought I'd throw in another 2 cents... light pollution by
              > itself isn't the biggest problem I face. It's that the light
              > pollution changes from region to region in the sky. This makes it
              > nearly impossible to effectively remove the gradients it causes. If
              > it was simple vignetting or a straight gradient, I could remove it
              > with software without much problem. But because of the local
              > pollution I encounter (street lights, neighbors' porch lights) and
              > the fact that the amount of pollution changes as I track an object
              > throughout the night, the gradients are all over the place.
              >
              > If I'm able to restrict imaging to a 2-3 hour window with the scope
              > pointing almost straight up, that's when things turn out the best. :)
              >
              > I just took a few 20-minute Ha images of M57 the other night (through
              > the TOA-130). The Ha filter gets rid of nearly all those darn
              > gradients but, of course, my targets are somewhat limited and I DO
              > still need to image longer than I would under darker skies. But I'll
              > take what I can get. :)
              >
              > I'll post the image once I get some more data (another 2-3 hours
              > worth, hopefully).
              >
              > BTW, if you haven't already ordered them already, I'd recommend the
              > TOA-35 flattener and the TOA/FS 2.7" reducer.
              >
              > Best,
              > Daniel Perry
              > http://www.californiastars.net/
              >
              >
              > --- In ccd-newastro@yahoogroups.com, "htrott" <trottier@...> wrote:
              >
              >> Hi Ron:
              >>
              >> Thanks for your quick reply, and also Jon's tip to look at
              >> Daniel Perry's site (I have before, and his results with
              >> the TOA-130 near LA are an inspiration!).
              >>
              >> I hope I can squeeze in a few follow-up questions, to help
              >> me nail this down.
              >>
              >> What about the ST-8, down slightly in resolution (to 1.85"/pixel at
              >> the native fratio of the TOA-130), and FOV, from the ST-10, but also
              >> down quite a bit in price? From what I can understand from the SBIG
              >> specs, the ST-8 does not have the microlenses that you pointed to
              >>
              > as a
              >
              >> bit of problem with the ST-10.
              >>
              >> In terms of dSLR's, I'm a little concerned about how difficult
              >> it will be to modify the camera, in order to remove the IR block
              >> and RGB filters. How much of a challenge is that (for someone
              >> with little equipment or experience)? I'm also unclear about just
              >> how much advantage one gets from the cooling of a dedicated imager,
              >> versus simply having the dark frames for a dSLR.
              >>
              >> In the comparison between the NABG and ABG cameras, does one just
              >> take the ratio of QE, squared, to determine the increased exposure
              >> time? I'm also not sure how to factor in the effects of light
              >> pollution, with a given limiting visual magnitude as input, though
              >> perhaps I'm trying to be overly theoretical at this point!
              >>
              >> Thanks for any additional input.
              >>
              >> Cheers,
              >> Howard.
              >>
              >> --- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@> wrote:
              >>
              >>> I think your analysis is on the mark - in light polluted skies,
              >>>
              > the
              >
              >> NABG
              >>
              >>> cameras are usually the better choice.
              >>>
              >>> The ST-10 is pretty much my first choice for refractors 6" and
              >>>
              > smaller.
              >
              >>> It has a good combination of pixel size and sensitivity. You do
              >>>
              > get
              >
              >> some
              >>
              >>> minor reflections from the microlenses that put short vertical
              >>>
              >> spikes on
              >>
              >>> the stars - SBIG's CCDOPS program has a utility for cleaning this
              >>>
              > up,
              >
              >>> but it's not user friendly.
              >>>
              >>> If money is an issue, then the new Canon Rebel xti makes a very
              >>>
              > good
              >
              >>> starter camera for most small refractors until you are ready to
              >>>
              > get a
              >
              >>> high-end camera.
              >>>
              >>> Ron Wodaski
              >>>
              >
              >
              >
              >
              > Yahoo! Groups Links
              >
              >
              >
              >
            • Andy Schlei
              Howard, ... I image from the middle of West Los Angeles, with serious light pollution. I have an ST-10XME which works quite well. I need many exposures to
              Message 6 of 23 , Jun 5, 2007
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                Howard,

                >
                > I will typically image in Vancouver, Canada, with fairly strong light
                > pollution (limiting visual magnitude about 5 near the zenith, at the
                > very best), and frequently moist atmospherics (how's that for modest
                > goals?!).
                >
                > My imaging goals range from wide-field galaxy clusters and nebulae,
                > to globulars, and individual galaxies with interesting morphologies
                > and lines-of sight. So my intention is to use the TOA-130 at its
                > native focal length, but also using either a Takahashi reducer or
                > extender to go to wider and smaller fields.
                >

                I image from the middle of West Los Angeles, with serious light
                pollution. I have an ST-10XME which works quite well. I need many
                exposures to overcome the light pollution, but I get decent results on
                galaxies and nebula. I use both a C-11 and an NP-101 on a Celestron
                CGE mount.

                NGC 891:
                http://obsballona.net/coppermine/displayimage.php?album=2&pos=11

                M 63:
                http://obsballona.net/coppermine/displayimage.php?album=2&pos=3

                Bubble Nebula
                http://obsballona.net/coppermine/displayimage.php?album=1&pos=9

                HTH,

                --Andy
                http://www.obsballona.org/
              • Andy Schlei
                Ron, ... spikes on ... Thanks, I now know where those spikes are coming from! Mystery solved... --Andy http://www.obsballona.org/
                Message 7 of 23 , Jun 5, 2007
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                  Ron,

                  > You do get some
                  > minor reflections from the microlenses that put short vertical
                  spikes on
                  > the stars - SBIG's CCDOPS program has a utility for cleaning this up,
                  > but it's not user friendly.

                  Thanks, I now know where those spikes are coming from! Mystery solved...

                  --Andy
                  http://www.obsballona.org/
                • Jim Miller
                  Very nice Andy. How short on your subs did you have to go? thanks, Jim ... From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com]On Behalf Of
                  Message 8 of 23 , Jun 5, 2007
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                    Very nice Andy. How short on your subs did you have to go?

                    thanks,

                    Jim
                    -----Original Message-----
                    From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com]On
                    Behalf Of Andy Schlei
                    Sent: Tuesday, June 05, 2007 11:22 AM
                    To: ccd-newastro@yahoogroups.com
                    Subject: [ccd-newastro] Re: Choice of SBIG for Takahashi TOA-130 in
                    light-polluted city skies?


                    Howard,

                    >
                    > I will typically image in Vancouver, Canada, with fairly strong light
                    > pollution (limiting visual magnitude about 5 near the zenith, at the
                    > very best), and frequently moist atmospherics (how's that for modest
                    > goals?!).
                    >
                    > My imaging goals range from wide-field galaxy clusters and nebulae,
                    > to globulars, and individual galaxies with interesting morphologies
                    > and lines-of sight. So my intention is to use the TOA-130 at its
                    > native focal length, but also using either a Takahashi reducer or
                    > extender to go to wider and smaller fields.
                    >

                    I image from the middle of West Los Angeles, with serious light
                    pollution. I have an ST-10XME which works quite well. I need many
                    exposures to overcome the light pollution, but I get decent results on
                    galaxies and nebula. I use both a C-11 and an NP-101 on a Celestron
                    CGE mount.

                    NGC 891:
                    http://obsballona.net/coppermine/displayimage.php?album=2&pos=11

                    M 63:
                    http://obsballona.net/coppermine/displayimage.php?album=2&pos=3

                    Bubble Nebula
                    http://obsballona.net/coppermine/displayimage.php?album=1&pos=9

                    HTH,

                    --Andy
                    http://www.obsballona.org/






                    [Non-text portions of this message have been removed]
                  • dannysperry
                    Andy, You re apparently surrounded by the 405, LAX, and Santa Monica Municipal... in regards to astrophotography and light pollution, the only thing you have
                    Message 9 of 23 , Jun 5, 2007
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                      Andy,

                      You're apparently surrounded by the 405, LAX, and Santa Monica
                      Municipal... in regards to astrophotography and light pollution, the
                      only thing you have going for you is the Pacific Ocean to the west!
                      With that in mind, you have my admiration because of the images
                      you've been able to get! Nicely done.

                      And, cool observatory, by the way!

                      Best,
                      Daniel Perry
                      http://www.californiastars.net/
                      34.04N 117.40W


                      --- In ccd-newastro@yahoogroups.com, "Andy Schlei" <andy_schlei@...>
                      wrote:
                      >
                      > Howard,
                      >
                      > >
                      > > I will typically image in Vancouver, Canada, with fairly strong
                      light
                      > > pollution (limiting visual magnitude about 5 near the zenith, at
                      the
                      > > very best), and frequently moist atmospherics (how's that for
                      modest
                      > > goals?!).
                      > >
                      > > My imaging goals range from wide-field galaxy clusters and
                      nebulae,
                      > > to globulars, and individual galaxies with interesting
                      morphologies
                      > > and lines-of sight. So my intention is to use the TOA-130 at its
                      > > native focal length, but also using either a Takahashi reducer or
                      > > extender to go to wider and smaller fields.
                      > >
                      >
                      > I image from the middle of West Los Angeles, with serious light
                      > pollution. I have an ST-10XME which works quite well. I need many
                      > exposures to overcome the light pollution, but I get decent results
                      on
                      > galaxies and nebula. I use both a C-11 and an NP-101 on a Celestron
                      > CGE mount.
                      >
                      > NGC 891:
                      > http://obsballona.net/coppermine/displayimage.php?album=2&pos=11
                      >
                      > M 63:
                      > http://obsballona.net/coppermine/displayimage.php?album=2&pos=3
                      >
                      > Bubble Nebula
                      > http://obsballona.net/coppermine/displayimage.php?album=1&pos=9
                      >
                      > HTH,
                      >
                      > --Andy
                      > http://www.obsballona.org/
                      >
                    • Andy Schlei
                      Jim, ... Thanks! I have been shooting 5 minute luminance and 3 minute R/G/B 2x2 binned. I admit that I struggle with the concept of going shorter to reduce the
                      Message 10 of 23 , Jun 6, 2007
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                        Jim,

                        > Very nice Andy. How short on your subs did you have to go?

                        Thanks!

                        I have been shooting 5 minute luminance and 3 minute R/G/B 2x2 binned.
                        I admit that I struggle with the concept of going shorter to reduce
                        the effects of light pollution. It seems counter intuitive to me. I
                        think that the CCDWare calculator would put me below a minute, but
                        that just seems to short when objects are in the thousands of ADU on a
                        five minute sub.

                        --Andy
                        http://www.obsballona.org/
                      • dannysperry
                        Thanks, Ron. I used Russ s GXT before and it worked quite well (I just used the trial version). I think it s time to pop for the full version. Here s the
                        Message 11 of 23 , Jun 6, 2007
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                          Thanks, Ron. I used Russ's GXT before and it worked quite well (I
                          just used the trial version). I think it's time to pop for the full
                          version. Here's the before and after:

                          Before:
                          http://www.californiastars.net/gallery/other/m097.m108_st2k_wom80_grad
                          ient.jpg

                          After:
                          http://www.californiastars.net/gallery/m097.m108_st2k_wom80.html

                          But that was a relatively simple, vignetting related gradient. I'll
                          have to give it a shot on some of the more complex gradients I've run
                          into.

                          Best,
                          Danny
                          http://www.californiastars.net/




                          --- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@...>
                          wrote:
                          >
                          > I used to image under skies like that. You should look at Russ
                          Croman's
                          > gradientXTerminator software - it work within Photoshop to clean up
                          even
                          > really messy gradients (which includes subtle gradients from bad
                          flats
                          > as well as grosser gradients from light pollution).
                          >
                          > See Russ's site at:
                          >
                          > http://www.rc-astro.com/resources/GradientXTerminator/index.html
                          >
                          > Ron Wodaski
                          >
                          > dannysperry wrote:
                          > > Hi Howard,
                          > >
                          > > Just thought I'd throw in another 2 cents... light pollution by
                          > > itself isn't the biggest problem I face. It's that the light
                          > > pollution changes from region to region in the sky. This makes it
                          > > nearly impossible to effectively remove the gradients it causes.
                          If
                          > > it was simple vignetting or a straight gradient, I could remove
                          it
                          > > with software without much problem. But because of the local
                          > > pollution I encounter (street lights, neighbors' porch lights)
                          and
                          > > the fact that the amount of pollution changes as I track an
                          object
                          > > throughout the night, the gradients are all over the place.
                          > >
                          > > If I'm able to restrict imaging to a 2-3 hour window with the
                          scope
                          > > pointing almost straight up, that's when things turn out the
                          best. :)
                          > >
                          > > I just took a few 20-minute Ha images of M57 the other night
                          (through
                          > > the TOA-130). The Ha filter gets rid of nearly all those darn
                          > > gradients but, of course, my targets are somewhat limited and I
                          DO
                          > > still need to image longer than I would under darker skies. But
                          I'll
                          > > take what I can get. :)
                          > >
                          > > I'll post the image once I get some more data (another 2-3 hours
                          > > worth, hopefully).
                          > >
                          > > BTW, if you haven't already ordered them already, I'd recommend
                          the
                          > > TOA-35 flattener and the TOA/FS 2.7" reducer.
                          > >
                          > > Best,
                          > > Daniel Perry
                          > > http://www.californiastars.net/
                          > >
                          > >
                          > > --- In ccd-newastro@yahoogroups.com, "htrott" <trottier@> wrote:
                          > >
                          > >> Hi Ron:
                          > >>
                          > >> Thanks for your quick reply, and also Jon's tip to look at
                          > >> Daniel Perry's site (I have before, and his results with
                          > >> the TOA-130 near LA are an inspiration!).
                          > >>
                          > >> I hope I can squeeze in a few follow-up questions, to help
                          > >> me nail this down.
                          > >>
                          > >> What about the ST-8, down slightly in resolution (to 1.85"/pixel
                          at
                          > >> the native fratio of the TOA-130), and FOV, from the ST-10, but
                          also
                          > >> down quite a bit in price? From what I can understand from the
                          SBIG
                          > >> specs, the ST-8 does not have the microlenses that you pointed
                          to
                          > >>
                          > > as a
                          > >
                          > >> bit of problem with the ST-10.
                          > >>
                          > >> In terms of dSLR's, I'm a little concerned about how difficult
                          > >> it will be to modify the camera, in order to remove the IR block
                          > >> and RGB filters. How much of a challenge is that (for someone
                          > >> with little equipment or experience)? I'm also unclear about just
                          > >> how much advantage one gets from the cooling of a dedicated
                          imager,
                          > >> versus simply having the dark frames for a dSLR.
                          > >>
                          > >> In the comparison between the NABG and ABG cameras, does one just
                          > >> take the ratio of QE, squared, to determine the increased
                          exposure
                          > >> time? I'm also not sure how to factor in the effects of light
                          > >> pollution, with a given limiting visual magnitude as input,
                          though
                          > >> perhaps I'm trying to be overly theoretical at this point!
                          > >>
                          > >> Thanks for any additional input.
                          > >>
                          > >> Cheers,
                          > >> Howard.
                          > >>
                          > >> --- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@>
                          wrote:
                          > >>
                          > >>> I think your analysis is on the mark - in light polluted skies,
                          > >>>
                          > > the
                          > >
                          > >> NABG
                          > >>
                          > >>> cameras are usually the better choice.
                          > >>>
                          > >>> The ST-10 is pretty much my first choice for refractors 6" and
                          > >>>
                          > > smaller.
                          > >
                          > >>> It has a good combination of pixel size and sensitivity. You do
                          > >>>
                          > > get
                          > >
                          > >> some
                          > >>
                          > >>> minor reflections from the microlenses that put short vertical
                          > >>>
                          > >> spikes on
                          > >>
                          > >>> the stars - SBIG's CCDOPS program has a utility for cleaning
                          this
                          > >>>
                          > > up,
                          > >
                          > >>> but it's not user friendly.
                          > >>>
                          > >>> If money is an issue, then the new Canon Rebel xti makes a very
                          > >>>
                          > > good
                          > >
                          > >>> starter camera for most small refractors until you are ready to
                          > >>>
                          > > get a
                          > >
                          > >>> high-end camera.
                          > >>>
                          > >>> Ron Wodaski
                          > >>>
                          > >
                          > >
                          > >
                          > >
                          > > Yahoo! Groups Links
                          > >
                          > >
                          > >
                          > >
                          >
                        • Richard Seavey
                          Andy The CCDWare calculator determines the minimum exposure time, not the maximum. You can expose as long as you want, but are usually limited by saturation
                          Message 12 of 23 , Jun 6, 2007
                          • 0 Attachment
                            Andy
                            The CCDWare calculator determines the minimum exposure time, not the
                            maximum. You can expose as long as you want, but are usually limited by
                            saturation effects (blooming) of bright objects. Also, the likelihood of
                            cosmic ray hits or airplane trails increases as sub frame exposures are
                            made longer. The technique of dithering the sub frames is a very big help
                            in eliminating cosmic ray hits and other artifacts. Dithering requires at
                            least 3 sub frames, and 10 or more will provide even better results. So,
                            determining the maximum exposure for a sub frame is somewhat harder. I
                            image in mag 4.5 skies and often use 10 minute exposures for luminance images.

                            Richard



                            At 03:30 PM 6/6/2007 +0000, you wrote:

                            >Jim,
                            >
                            > > Very nice Andy. How short on your subs did you have to go?
                            >
                            >Thanks!
                            >
                            >I have been shooting 5 minute luminance and 3 minute R/G/B 2x2 binned.
                            >I admit that I struggle with the concept of going shorter to reduce
                            >the effects of light pollution. It seems counter intuitive to me. I
                            >think that the CCDWare calculator would put me below a minute, but
                            >that just seems to short when objects are in the thousands of ADU on a
                            >five minute sub.
                            >
                            >--Andy
                          • Andy Schlei
                            Richard, ... At one point I had been told (by Ron, I think) that to minimize light pollution problems one should use the minimum exposure time from the
                            Message 13 of 23 , Jun 6, 2007
                            • 0 Attachment
                              Richard,

                              > The CCDWare calculator determines the minimum exposure time, not the
                              > maximum. You can expose as long as you want, but are usually limited by
                              > saturation effects (blooming) of bright objects.

                              At one point I had been told (by Ron, I think) that to minimize light
                              pollution problems one should use the minimum exposure time from the
                              calculator. I understood that the aim was to get to as long an
                              exposure as possible without having sky glow dominate the image.

                              My background on a not very transparent night was 3,790 ADU from a 5
                              minute exposure with an ST-10. The calculator recommends a 32.4
                              second exposure. Note that the galaxy in my image averaged only 4,400
                              ADU, with a peak value of ~15,000. I'd have almost no signal at 32
                              seconds, so your point makes sense, that the 32 seconds is the minimum
                              exposure.

                              I have found that if I am binning my color shots I get better results
                              with 3 minute exposures rather than 5 minute ones.

                              --Andy
                              http://www.obsballona.org/
                            • Andy Schlei
                              Daniel, ... Thanks! The ocean does help. Thankfully no one has managed to put lights out there. Clear skies, --Andy http://www.obsballona.org/
                              Message 14 of 23 , Jun 6, 2007
                              • 0 Attachment
                                Daniel,

                                >
                                > You're apparently surrounded by the 405, LAX, and Santa Monica
                                > Municipal... in regards to astrophotography and light pollution, the
                                > only thing you have going for you is the Pacific Ocean to the west!
                                > With that in mind, you have my admiration because of the images
                                > you've been able to get! Nicely done.
                                >
                                >
                                > And, cool observatory, by the way!

                                Thanks!

                                The ocean does help. Thankfully no one has managed to put lights out
                                there.

                                Clear skies,

                                --Andy
                                http://www.obsballona.org/
                              • Yahoo - Wodaski
                                See below. Ron Wodaski ... No, that s not how it works. The aim is to make sure your sub-exposures are long enough for the shot noise (including light
                                Message 15 of 23 , Jun 6, 2007
                                • 0 Attachment
                                  See below.

                                  Ron Wodaski

                                  Andy Schlei wrote:
                                  > Richard,
                                  >
                                  >
                                  >> The CCDWare calculator determines the minimum exposure time, not the
                                  >> maximum. You can expose as long as you want, but are usually limited by
                                  >> saturation effects (blooming) of bright objects.
                                  >>
                                  >
                                  > At one point I had been told (by Ron, I think) that to minimize light
                                  > pollution problems one should use the minimum exposure time from the
                                  > calculator. I understood that the aim was to get to as long an
                                  > exposure as possible without having sky glow dominate the image.
                                  >
                                  No, that's not how it works. The aim is to make sure your sub-exposures
                                  are long enough for the shot noise (including light pollution) to swamp
                                  the read noise. The next aim is to take as many exposures as possible so
                                  that you can combine them to minimize total noise.
                                  > My background on a not very transparent night was 3,790 ADU from a 5
                                  > minute exposure with an ST-10. The calculator recommends a 32.4
                                  > second exposure. Note that the galaxy in my image averaged only 4,400
                                  > ADU, with a peak value of ~15,000. I'd have almost no signal at 32
                                  > seconds, so your point makes sense, that the 32 seconds is the minimum
                                  > exposure.
                                  >
                                  Your skies are very bright, then. For convenience, you can certainly
                                  take exposure longer than 32 seconds, but it will be the total exposure
                                  time that will determine how deep you can go.
                                  > I have found that if I am binning my color shots I get better results
                                  > with 3 minute exposures rather than 5 minute ones.
                                  >
                                  > --Andy
                                  > http://www.obsballona.org/
                                  >
                                  >
                                  >
                                  >
                                  >
                                  >
                                  > Yahoo! Groups Links
                                  >
                                  >
                                  >
                                  >
                                • Andy Schlei
                                  Ron, ... possible so ... Thanks Ron, that makes complete sense to me. If I have 500 or so ADUs between object and background, then I should get as much
                                  Message 16 of 23 , Jun 6, 2007
                                  • 0 Attachment
                                    Ron,


                                    > No, that's not how it works. The aim is to make sure your sub-exposures
                                    > are long enough for the shot noise (including light pollution) to swamp
                                    > the read noise. The next aim is to take as many exposures as
                                    possible so
                                    > that you can combine them to minimize total noise.

                                    > Your skies are very bright, then. For convenience, you can certainly
                                    > take exposure longer than 32 seconds, but it will be the total exposure
                                    > time that will determine how deep you can go.


                                    Thanks Ron, that makes complete sense to me. If I have 500 or so ADUs
                                    between object and background, then I should get as much exposure time
                                    as possible to have enough data to tease out the object details from
                                    the background. And with the bright skies, I have to expect that
                                    faint parts of objects may be so close to the background it will be
                                    hard to image at all.

                                    P.S., As you have said, Russ Croman's GradientXterminator is an
                                    essential tool for dealing with light pollution gradients. It works
                                    like magic. The Dynamic Background Extractor in PixInsight is quite
                                    good too, but requires more work.

                                    --Andy
                                    http://www.obsballona.org/
                                  • Jim Miller
                                    Thanks Andy, I have dropped my lum subs to 5 minutes as well. Now I am considering moving from an ST-2000XM to an ST10 because of it. I think my CCDWARE
                                    Message 17 of 23 , Jun 6, 2007
                                    • 0 Attachment
                                      Thanks Andy, I have dropped my lum subs to 5 minutes as well. Now I am
                                      considering moving from an ST-2000XM to an ST10 because of it. I think my
                                      CCDWARE calculator had me at 2 minutes.

                                      Thanks,

                                      Jim



                                      -----Original Message-----
                                      From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com]On
                                      Behalf Of Andy Schlei
                                      Sent: Wednesday, June 06, 2007 9:30 AM
                                      To: ccd-newastro@yahoogroups.com
                                      Subject: [ccd-newastro] Re: Choice of SBIG for Takahashi TOA-130 in
                                      light-polluted city skies?


                                      Jim,

                                      > Very nice Andy. How short on your subs did you have to go?

                                      Thanks!

                                      I have been shooting 5 minute luminance and 3 minute R/G/B 2x2 binned.
                                      I admit that I struggle with the concept of going shorter to reduce
                                      the effects of light pollution. It seems counter intuitive to me. I
                                      think that the CCDWare calculator would put me below a minute, but
                                      that just seems to short when objects are in the thousands of ADU on a
                                      five minute sub.

                                      --Andy
                                      http://www.obsballona.org/






                                      [Non-text portions of this message have been removed]
                                    • Jim Miller
                                      Wow, nice result. Which detail and aggressiveness setting did you use. Nice pic by the way. Jim ... From: ccd-newastro@yahoogroups.com
                                      Message 18 of 23 , Jun 6, 2007
                                      • 0 Attachment
                                        Wow, nice result. Which detail and aggressiveness setting did you use.

                                        Nice pic by the way.

                                        Jim
                                        -----Original Message-----
                                        From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com]On
                                        Behalf Of dannysperry
                                        Sent: Wednesday, June 06, 2007 10:57 AM
                                        To: ccd-newastro@yahoogroups.com
                                        Subject: [ccd-newastro] Re: Choice of SBIG for Takahashi TOA-130 in
                                        light-polluted city skies?


                                        Thanks, Ron. I used Russ's GXT before and it worked quite well (I
                                        just used the trial version). I think it's time to pop for the full
                                        version. Here's the before and after:

                                        Before:
                                        http://www.californiastars.net/gallery/other/m097.m108_st2k_wom80_grad
                                        ient.jpg

                                        After:
                                        http://www.californiastars.net/gallery/m097.m108_st2k_wom80.html

                                        But that was a relatively simple, vignetting related gradient. I'll
                                        have to give it a shot on some of the more complex gradients I've run
                                        into.

                                        Best,
                                        Danny
                                        http://www.californiastars.net/

                                        --- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@...>
                                        wrote:
                                        >
                                        > I used to image under skies like that. You should look at Russ
                                        Croman's
                                        > gradientXTerminator software - it work within Photoshop to clean up
                                        even
                                        > really messy gradients (which includes subtle gradients from bad
                                        flats
                                        > as well as grosser gradients from light pollution).
                                        >
                                        > See Russ's site at:
                                        >
                                        > http://www.rc-astro.com/resources/GradientXTerminator/index.html
                                        >
                                        > Ron Wodaski
                                        >
                                        > dannysperry wrote:
                                        > > Hi Howard,
                                        > >
                                        > > Just thought I'd throw in another 2 cents... light pollution by
                                        > > itself isn't the biggest problem I face. It's that the light
                                        > > pollution changes from region to region in the sky. This makes it
                                        > > nearly impossible to effectively remove the gradients it causes.
                                        If
                                        > > it was simple vignetting or a straight gradient, I could remove
                                        it
                                        > > with software without much problem. But because of the local
                                        > > pollution I encounter (street lights, neighbors' porch lights)
                                        and
                                        > > the fact that the amount of pollution changes as I track an
                                        object
                                        > > throughout the night, the gradients are all over the place.
                                        > >
                                        > > If I'm able to restrict imaging to a 2-3 hour window with the
                                        scope
                                        > > pointing almost straight up, that's when things turn out the
                                        best. :)
                                        > >
                                        > > I just took a few 20-minute Ha images of M57 the other night
                                        (through
                                        > > the TOA-130). The Ha filter gets rid of nearly all those darn
                                        > > gradients but, of course, my targets are somewhat limited and I
                                        DO
                                        > > still need to image longer than I would under darker skies. But
                                        I'll
                                        > > take what I can get. :)
                                        > >
                                        > > I'll post the image once I get some more data (another 2-3 hours
                                        > > worth, hopefully).
                                        > >
                                        > > BTW, if you haven't already ordered them already, I'd recommend
                                        the
                                        > > TOA-35 flattener and the TOA/FS 2.7" reducer.
                                        > >
                                        > > Best,
                                        > > Daniel Perry
                                        > > http://www.californiastars.net/
                                        > >
                                        > >
                                        > > --- In ccd-newastro@yahoogroups.com, "htrott" <trottier@> wrote:
                                        > >
                                        > >> Hi Ron:
                                        > >>
                                        > >> Thanks for your quick reply, and also Jon's tip to look at
                                        > >> Daniel Perry's site (I have before, and his results with
                                        > >> the TOA-130 near LA are an inspiration!).
                                        > >>
                                        > >> I hope I can squeeze in a few follow-up questions, to help
                                        > >> me nail this down.
                                        > >>
                                        > >> What about the ST-8, down slightly in resolution (to 1.85"/pixel
                                        at
                                        > >> the native fratio of the TOA-130), and FOV, from the ST-10, but
                                        also
                                        > >> down quite a bit in price? From what I can understand from the
                                        SBIG
                                        > >> specs, the ST-8 does not have the microlenses that you pointed
                                        to
                                        > >>
                                        > > as a
                                        > >
                                        > >> bit of problem with the ST-10.
                                        > >>
                                        > >> In terms of dSLR's, I'm a little concerned about how difficult
                                        > >> it will be to modify the camera, in order to remove the IR block
                                        > >> and RGB filters. How much of a challenge is that (for someone
                                        > >> with little equipment or experience)? I'm also unclear about just
                                        > >> how much advantage one gets from the cooling of a dedicated
                                        imager,
                                        > >> versus simply having the dark frames for a dSLR.
                                        > >>
                                        > >> In the comparison between the NABG and ABG cameras, does one just
                                        > >> take the ratio of QE, squared, to determine the increased
                                        exposure
                                        > >> time? I'm also not sure how to factor in the effects of light
                                        > >> pollution, with a given limiting visual magnitude as input,
                                        though
                                        > >> perhaps I'm trying to be overly theoretical at this point!
                                        > >>
                                        > >> Thanks for any additional input.
                                        > >>
                                        > >> Cheers,
                                        > >> Howard.
                                        > >>
                                        > >> --- In ccd-newastro@yahoogroups.com, Yahoo - Wodaski <yahoo@>
                                        wrote:
                                        > >>
                                        > >>> I think your analysis is on the mark - in light polluted skies,
                                        > >>>
                                        > > the
                                        > >
                                        > >> NABG
                                        > >>
                                        > >>> cameras are usually the better choice.
                                        > >>>
                                        > >>> The ST-10 is pretty much my first choice for refractors 6" and
                                        > >>>
                                        > > smaller.
                                        > >
                                        > >>> It has a good combination of pixel size and sensitivity. You do
                                        > >>>
                                        > > get
                                        > >
                                        > >> some
                                        > >>
                                        > >>> minor reflections from the microlenses that put short vertical
                                        > >>>
                                        > >> spikes on
                                        > >>
                                        > >>> the stars - SBIG's CCDOPS program has a utility for cleaning
                                        this
                                        > >>>
                                        > > up,
                                        > >
                                        > >>> but it's not user friendly.
                                        > >>>
                                        > >>> If money is an issue, then the new Canon Rebel xti makes a very
                                        > >>>
                                        > > good
                                        > >
                                        > >>> starter camera for most small refractors until you are ready to
                                        > >>>
                                        > > get a
                                        > >
                                        > >>> high-end camera.
                                        > >>>
                                        > >>> Ron Wodaski
                                        > >>>
                                        > >
                                        > >
                                        > >
                                        > >
                                        > > Yahoo! Groups Links
                                        > >
                                        > >
                                        > >
                                        > >
                                        >






                                        [Non-text portions of this message have been removed]
                                      • htrott
                                        Hi: I appreciate the many helpful replies in connection with this message thread, and the one I asked earlier about the choice of scope. I put my order in just
                                        Message 19 of 23 , Jun 7, 2007
                                        • 0 Attachment
                                          Hi:

                                          I appreciate the many helpful replies in connection with this message
                                          thread, and the one I asked earlier about the choice of scope.

                                          I put my order in just today for a Takahashi TOA-130, with EM-200
                                          Temma II mount, and SBIG ST-2000XM camera! I am also getting the Tak
                                          reducer, extender, and flattener.

                                          Although the ST-10 has its virtues, I opted in the end for the lower
                                          price on ST-2000, and will accept the limitations in light-polluted
                                          skies of its ABG feature (and somewhat larger pixel size), although
                                          the convenience of not having to clean up blooms is a plus. Thanks for
                                          Ron for the detailed discussions on this and other crucial points.

                                          I also really enjoyed seeing what others have been able to do under
                                          heavily light-polluted skies, and with comparable equipment,
                                          especially Daniel Perry, Andy Schlei, and Mel Martin. This provides
                                          much to look forward to, as I continue to mount the imaging and image
                                          processing learning curves.

                                          I'll report back when I have some images from the near gear.

                                          Cheers,
                                          Howard Trottier
                                        • Joe Mize
                                          Howard, since you settled on the ST-2000 look at the STL4020XM before you buy, that is if you can afford the jump in price. A neighbor has one for his
                                          Message 20 of 23 , Jun 8, 2007
                                          • 0 Attachment
                                            Howard, since you settled on the ST-2000 look at the STL4020XM before you
                                            buy, that is if you can afford the jump in price. A neighbor has one for
                                            his TOA-130, fantastic...joe :)

                                            "May You Go Among The Imperishable Stars"

                                            Joe Mize
                                            StarFields Observatory http://www.cav-sfo.com/
                                            Chiefland, FL 29:24'33.4"N 82:51'37.7"W

                                            -----Original Message-----
                                            From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com]On
                                            Behalf Of htrott
                                            Sent: Thursday, June 07, 2007 10:38 PM
                                            To: ccd-newastro@yahoogroups.com
                                            Subject: [ccd-newastro] Re: Choice of SBIG for Takahashi TOA-130 in
                                            light-polluted city skies?

                                            Hi:

                                            I appreciate the many helpful replies in connection with this message
                                            thread, and the one I asked earlier about the choice of scope.

                                            I put my order in just today for a Takahashi TOA-130, with EM-200
                                            Temma II mount, and SBIG ST-2000XM camera! I am also getting the Tak
                                            reducer, extender, and flattener.

                                            Although the ST-10 has its virtues, I opted in the end for the lower
                                            price on ST-2000, and will accept the limitations in light-polluted
                                            skies of its ABG feature (and somewhat larger pixel size), although
                                            the convenience of not having to clean up blooms is a plus. Thanks for
                                            Ron for the detailed discussions on this and other crucial points.

                                            I also really enjoyed seeing what others have been able to do under
                                            heavily light-polluted skies, and with comparable equipment,
                                            especially Daniel Perry, Andy Schlei, and Mel Martin. This provides
                                            much to look forward to, as I continue to mount the imaging and image
                                            processing learning curves.

                                            I'll report back when I have some images from the near gear.

                                            Cheers,
                                            Howard Trottier



                                            Yahoo! Groups Links
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