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guiding techniques

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  • Kevin Dixon
    Good Morning Ron: I have a few questions regarding guiding while using a CCD camera. If the camera is being used with an 8 SCT at a focal ratio of f/10 or
    Message 1 of 4 , Aug 1, 2000
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      Good Morning Ron:

      I have a few questions regarding guiding while using a CCD camera.
      If the camera is being used with an 8" SCT at a focal ratio of f/10
      or f/6.3, can a guidescope be used or is it better to use an off-axis
      guider (or similar device).

      Also, if the ST-237 is used with the Fastar lens assembly, it seems
      that guiding would be done via a guidescope. Is this correct?

      Clear skies,
      Kevin
      ksbtk@...
    • Ron Wodaski
      Because the mirror of an SCT shifts for a variety of reasons, and can shift even during an exposure, it s not possible to maintain alignment between a
      Message 2 of 4 , Aug 1, 2000
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        Because the mirror of an SCT shifts for a variety of reasons, and can shift
        even during an exposure, it's not possible to maintain alignment between a
        guidescope and an SCT. In other words, you either need to use a setup that
        puts the guider in the same light path. That could be a camera with an
        integrated guider (SBIG ST-7/8/9), or an off-axis guider. The SBIG camera's
        are the simplest solution.

        You can also stick with unguided exposures, and throw out any that show
        mirror shift problems.

        The longer your focal length, the more critical good guiding is. In the case
        of the Fastar, you are shooting at a very short focal length (400mm), and it
        is quite possible to take 1-2 minute unguided exposures successfully. I have
        gotten good results this way, including color images, by stacking the
        unguided exposures.

        The alternative is to lock the mirror in place, and use some other device
        for focusing (e.g., a Crayford focuser on the back; the NGF-S motorized,
        etc.).

        The most common application for using a guidescope successfully is when two
        refractors are involved; it is relatively easy to make that kind of assembly
        rigid and reliable. However, even something like a cheap focuser can throw
        off a guidescope combination, and modifications to increase rigidity are
        common.

        Ron Wodaski
        The New Astronomy Book Site - http://www.newastro.com



        -----Original Message-----
        From: Kevin Dixon [mailto:ksbtk@...]
        Sent: Tuesday, August 01, 2000 1:55 AM
        To: ccd-newastro@egroups.com
        Subject: [ccd-newastro] guiding techniques


        Good Morning Ron:

        I have a few questions regarding guiding while using a CCD camera.
        If the camera is being used with an 8" SCT at a focal ratio of f/10
        or f/6.3, can a guidescope be used or is it better to use an off-axis
        guider (or similar device).

        Also, if the ST-237 is used with the Fastar lens assembly, it seems
        that guiding would be done via a guidescope. Is this correct?

        Clear skies,
        Kevin
        ksbtk@...





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      • Focus
        Hi Ron, Speaking of guiding, what is the increment or measurement in maxim in guide window that changes when you are guiding? It is the x and y box? I am not
        Message 3 of 4 , Aug 1, 2000
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          Hi Ron,
          Speaking of guiding, what is the increment or measurement in maxim in guide
          window that changes when you are guiding? It is the x and y box? I am not
          sure if I got good guiding....
          thanks
          Brian
          ----- Original Message -----
          From: Ron Wodaski <ronw@...>
          To: <ccd-newastro@egroups.com>
          Sent: Tuesday, August 01, 2000 9:04 AM
          Subject: RE: [ccd-newastro] guiding techniques


          > Because the mirror of an SCT shifts for a variety of reasons, and can
          shift
          > even during an exposure, it's not possible to maintain alignment between a
          > guidescope and an SCT. In other words, you either need to use a setup that
          > puts the guider in the same light path. That could be a camera with an
          > integrated guider (SBIG ST-7/8/9), or an off-axis guider. The SBIG
          camera's
          > are the simplest solution.
          >
          > You can also stick with unguided exposures, and throw out any that show
          > mirror shift problems.
          >
          > The longer your focal length, the more critical good guiding is. In the
          case
          > of the Fastar, you are shooting at a very short focal length (400mm), and
          it
          > is quite possible to take 1-2 minute unguided exposures successfully. I
          have
          > gotten good results this way, including color images, by stacking the
          > unguided exposures.
          >
          > The alternative is to lock the mirror in place, and use some other device
          > for focusing (e.g., a Crayford focuser on the back; the NGF-S motorized,
          > etc.).
          >
          > The most common application for using a guidescope successfully is when
          two
          > refractors are involved; it is relatively easy to make that kind of
          assembly
          > rigid and reliable. However, even something like a cheap focuser can throw
          > off a guidescope combination, and modifications to increase rigidity are
          > common.
          >
          > Ron Wodaski
          > The New Astronomy Book Site - http://www.newastro.com
          >
          >
          >
          > -----Original Message-----
          > From: Kevin Dixon [mailto:ksbtk@...]
          > Sent: Tuesday, August 01, 2000 1:55 AM
          > To: ccd-newastro@egroups.com
          > Subject: [ccd-newastro] guiding techniques
          >
          >
          > Good Morning Ron:
          >
          > I have a few questions regarding guiding while using a CCD camera.
          > If the camera is being used with an 8" SCT at a focal ratio of f/10
          > or f/6.3, can a guidescope be used or is it better to use an off-axis
          > guider (or similar device).
          >
          > Also, if the ST-237 is used with the Fastar lens assembly, it seems
          > that guiding would be done via a guidescope. Is this correct?
          >
          > Clear skies,
          > Kevin
          > ksbtk@...
          >
          >
          >
          >
          >
          > To unsubscribe from this group, send an email to:
          > ccd-newastro-unsubscribe@egroups.com
          >
          >
          >
          >
          >
          >
          >
          > To unsubscribe from this group, send an email to:
          > ccd-newastro-unsubscribe@egroups.com
          >
          >
          >
        • Ron Wodaski
          Yes, it s in the X and Y boxes. You can choose to display either pixels or arc-seconds (you ll need to enter telescope data to get accurate arc-second
          Message 4 of 4 , Aug 1, 2000
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            Yes, it's in the X and Y boxes. You can choose to display either pixels or
            arc-seconds (you'll need to enter telescope data to get accurate arc-second
            numbers).

            You can also select to have the guide corrections written to a file for
            later examination in detail; that's the best method for troubleshooting,
            since you have a complete record of the guiding session. I don't have the
            camera hooked up just now, but I think these options are available from the
            Settings button on the Guide panel, and then choose More for the logging
            option.

            Ron Wodaski
            The New Astronomy Book Site - http://www.newastro.com



            -----Original Message-----
            From: Focus [mailto:focus@...]
            Sent: Tuesday, August 01, 2000 8:04 AM
            To: ccd-newastro@egroups.com
            Subject: Re: [ccd-newastro] guiding techniques


            Hi Ron,
            Speaking of guiding, what is the increment or measurement in maxim in guide
            window that changes when you are guiding? It is the x and y box? I am not
            sure if I got good guiding....
            thanks
            Brian
            ----- Original Message -----
            From: Ron Wodaski <ronw@...>
            To: <ccd-newastro@egroups.com>
            Sent: Tuesday, August 01, 2000 9:04 AM
            Subject: RE: [ccd-newastro] guiding techniques


            > Because the mirror of an SCT shifts for a variety of reasons, and can
            shift
            > even during an exposure, it's not possible to maintain alignment between a
            > guidescope and an SCT. In other words, you either need to use a setup that
            > puts the guider in the same light path. That could be a camera with an
            > integrated guider (SBIG ST-7/8/9), or an off-axis guider. The SBIG
            camera's
            > are the simplest solution.
            >
            > You can also stick with unguided exposures, and throw out any that show
            > mirror shift problems.
            >
            > The longer your focal length, the more critical good guiding is. In the
            case
            > of the Fastar, you are shooting at a very short focal length (400mm), and
            it
            > is quite possible to take 1-2 minute unguided exposures successfully. I
            have
            > gotten good results this way, including color images, by stacking the
            > unguided exposures.
            >
            > The alternative is to lock the mirror in place, and use some other device
            > for focusing (e.g., a Crayford focuser on the back; the NGF-S motorized,
            > etc.).
            >
            > The most common application for using a guidescope successfully is when
            two
            > refractors are involved; it is relatively easy to make that kind of
            assembly
            > rigid and reliable. However, even something like a cheap focuser can throw
            > off a guidescope combination, and modifications to increase rigidity are
            > common.
            >
            > Ron Wodaski
            > The New Astronomy Book Site - http://www.newastro.com
            >
            >
            >
            > -----Original Message-----
            > From: Kevin Dixon [mailto:ksbtk@...]
            > Sent: Tuesday, August 01, 2000 1:55 AM
            > To: ccd-newastro@egroups.com
            > Subject: [ccd-newastro] guiding techniques
            >
            >
            > Good Morning Ron:
            >
            > I have a few questions regarding guiding while using a CCD camera.
            > If the camera is being used with an 8" SCT at a focal ratio of f/10
            > or f/6.3, can a guidescope be used or is it better to use an off-axis
            > guider (or similar device).
            >
            > Also, if the ST-237 is used with the Fastar lens assembly, it seems
            > that guiding would be done via a guidescope. Is this correct?
            >
            > Clear skies,
            > Kevin
            > ksbtk@...
            >
            >
            >
            >
            >
            > To unsubscribe from this group, send an email to:
            > ccd-newastro-unsubscribe@egroups.com
            >
            >
            >
            >
            >
            >
            >
            > To unsubscribe from this group, send an email to:
            > ccd-newastro-unsubscribe@egroups.com
            >
            >
            >




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