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

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  • 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 1 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 2 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 3 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 4 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 5 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 6 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 7 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 8 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 9 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 10 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 11 of 23 , Jun 6, 2007
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                          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 12 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 13 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 14 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 15 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 16 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 17 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 18 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 19 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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