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Re: Ritchey Chrtien collimation offset i don't understand

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  • Randy Nulman
    Hi Sandy, I think we are saying the same things, but in different ways. Yes, one wants to center the black blot (as I indicated, somewhat asymmetrical
    Message 1 of 6 , Jan 31, 2007
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      Hi Sandy,
      I think we are saying the same things, but in different ways. <G>

      Yes, one wants to center the black "blot" (as I indicated, somewhat
      asymmetrical due to it's nature). However there is also a
      black "dot" that is pure round and reflects in the center...this is
      the reflection of the Tak Collimating scope itself, and is often
      confused with the "real blot" you refer to. Also, since this "dot"
      reflection is centered, it usually will appear to "overlap" the blot
      (or the other way around). However, even then, the "blot" is still
      usually visible in the center.

      Does this make sense?

      Regards,
      Randy
      http://rc20.stonehenge-obs.com


      --- In ccd-newastro@yahoogroups.com, "Frank S Barnes III"
      <SBarnes@...> wrote:
      >
      > Hi Randy,
      >
      > The first part of your explanation I agree with, but the
      second
      > part I differ with. On a RCOS scope, the center of the secondary
      mirror
      > will have a actual circle drawn on it that you can see in the Tak
      > scope. The "dab of black" on the secondary is what the black magic
      > marker type pen leaves behind when the mirror is backed off the
      lathe
      > (the pen being inserted in the lathe to apply the center mark). So
      when
      > you are centering the secondary, you center the circle (which is
      the
      > "blot") in the Tak scope. Then you finish with the primary as you
      > described. There is a video on the RCOS website that shows this and
      > demonstrates how you collimate a RCOS RC.
      >
      >
      >
      > >On Wed, 31 Jan 2007 12:00:50 +0000, ccd-newastro@yahoogroups.com
      wrote:
      >
      >
      >____________________________________________________________________
      ____
      > >
      > >5c. Re: Ritchey Chr‚tien collimation offset i don't understand
      > > Posted by: "Randy Nulman" rj.nulman@... randy_nulman
      > > Date: Tue Jan 30, 2007 12:52 pm ((PST))
      > >
      > >Hi,
      > >First, the secondary must be totally centered, typically using
      > >measurements of the distance from each spider vane end to the
      tube.
      > >(all should be equally distanced).
      > >
      > >Then, the tip/tilt of the secondary may be necessary to
      align/center
      > >the "blot" to the center of the collimation scope.
      > >
      > >Be sure you are looking at the "blot" (which is assymetrical) as
      > >opposed to the purely round reflection of the collimation scope's
      > >center. This is typically where people get confused...The
      > >central "blot" on the secondary is NOT purely round as it's a dab
      of
      > >black on the secondary via a "marks-a-lot" scenario. Eventually,
      the
      > >pure round reflection of the collimation scope _and_ the "blot"
      will
      > >align/overlap closely with each other.
      > >
      > >Once the secondary is centered, then it's a simple matter of
      adjusting
      > >the primary tip/tilt until the whole "circle" is centered within
      the
      > >view of the collimation scope.
      > >
      > >Hope this helps,
      > >
      > >Randy Nulman
      > >http://rc20.stonehenge-obs.com
      > >
      > >
      >
      > Clear Skies ..........
      >
      > Klaatu Barada Nikto ....
      >
      > Frank S(Sandy) Barnes III
      > SBarnes@...
      > http://www.SkyImager.Com
      >
    • Mike Ford
      I was curious to find out how often you collimate your 20 . I haven t collimated our 20 since we first installed it over two years ago. Mike
      Message 2 of 6 , Feb 1 7:23 AM
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        I was curious to find out how often you collimate your 20". I haven't collimated our 20" since we first installed it over two years ago.

        Mike

        On Wednesday, January 31, 2007 7:05 PM, Ken Crawford <kenc@...> wrote:
        >
        >
        >
        >Here is the link to the collimation video...
        >
        >http://gallery.rcopticalsystems.com/video/RCOS_Collimation_V3.wmv
        >
        > Hope that helps,
        >
        > Ken Crawford
        >
        > --- In ccd-newastro@yahoogroups.com, "Frank S Barnes III"
        ><SBarnes@...> wrote:
        >>
        >> Hi Randy,
        >>
        >> The first part of your explanation I agree with, but the
        > second
        >> part I differ with. On a RCOS scope, the center of the secondary
        > mirror
        >> will have a actual circle drawn on it that you can see in the Tak
        >> scope. The "dab of black" on the secondary is what the black magic
        >> marker type pen leaves behind when the mirror is backed off the
        > lathe
        >> (the pen being inserted in the lathe to apply the center mark). So
        > when
        >> you are centering the secondary, you center the circle (which is
        > the
        >> "blot") in the Tak scope. Then you finish with the primary as you
        >> described. There is a video on the RCOS website that shows this and
        >> demonstrates how you collimate a RCOS RC.
        >>
        >>
        >>
        >> >On Wed, 31 Jan 2007 12:00:50 ;0000, ccd-newastro@yahoogroups.com
        > wrote:
        >>
        >>
        >>__________________________________________________________
        > ____
        >> >
        >> >5c. Re: Ritchey Chr‚tien collimation offset i don't understand
        >> > Posted by: "Randy Nulman" rj.nulman@... randy_nulman
        >> > Date: Tue Jan 30, 2007 12:52 pm ((PST))
        >> >
        >> >Hi,
        >> >First, the secondary must be totally centered, typically using
        >> >measurements of the distance from each spider vane end to the
        > tube.
        >> >(all should be equally distanced).
        >> >
        >> >Then, the tip/tilt of the secondary may be necessary to
        > align/center
        >> >the "blot" to the center of the collimation scope.
        >> >
        >> >Be sure you are looking at the "blot" (which is assymetrical) as
        >> >opposed to the purely round reflection of the collimation scope's
        >> >center. This is typically where people get confused...The
        >> >central "blot" on the secondary is NOT purely round as it's a dab
        > of
        >> >black on the secondary via a "marks-a-lot" scenario. Eventually,
        > the
        >> >pure round reflection of the collimation scope _and_ the "blot"
        > will
        >> >align/overlap closely with each other.
        >> >
        >> >Once the secondary is centered, then it's a simple matter of
        > adjusting
        >> >the primary tip/tilt until the whole "circle" is centered within
        > the
        >> >view of the collimation scope.
        >> >
        >> >Hope this helps,
        >> >
        >> >Randy Nulman
        >> >http://rc20.stonehenge-obs.com
        >> >
        >> >
        >>
        >> Clear Skies ..........
        >>
        >> Klaatu Barada Nikto ....
        >>
        >> Frank S(Sandy) Barnes III
        >> SBarnes@...
        >> http://www.SkyImager.Com
        >>
        >
        >
      • Ken Crawford
        Sandy in the collimation vidoe, Brad and I decided to rename the blot as this can be a confusing term. The video shows footage of the process and you can see
        Message 3 of 6 , Feb 1 8:38 AM
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          Sandy in the collimation vidoe, Brad and I decided to rename the
          blot as this can be a confusing term. The video shows footage of
          the process and you can see it very well. Sometimes the picture is
          worth 1000 words and a Video is worth 1000 pictures :)

          http://gallery.rcopticalsystems.com/video/RCOS_Collimation_V3.wmv

          Regards,

          Ken Crawford

          --- In ccd-newastro@yahoogroups.com, "Randy Nulman" <rj.nulman@...>
          wrote:
          >
          > Hi Sandy,
          > I think we are saying the same things, but in different ways. <G>
          >
          > Yes, one wants to center the black "blot" (as I indicated,
          somewhat
          > asymmetrical due to it's nature). However there is also a
          > black "dot" that is pure round and reflects in the center...this
          is
          > the reflection of the Tak Collimating scope itself, and is often
          > confused with the "real blot" you refer to. Also, since
          this "dot"
          > reflection is centered, it usually will appear to "overlap" the
          blot
          > (or the other way around). However, even then, the "blot" is
          still
          > usually visible in the center.
          >
          > Does this make sense?
          >
          > Regards,
          > Randy
          > http://rc20.stonehenge-obs.com
          >
          >
          > --- In ccd-newastro@yahoogroups.com, "Frank S Barnes III"
          > <SBarnes@> wrote:
          > >
          > > Hi Randy,
          > >
          > > The first part of your explanation I agree with, but the
          > second
          > > part I differ with. On a RCOS scope, the center of the secondary
          > mirror
          > > will have a actual circle drawn on it that you can see in the Tak
          > > scope. The "dab of black" on the secondary is what the black
          magic
          > > marker type pen leaves behind when the mirror is backed off the
          > lathe
          > > (the pen being inserted in the lathe to apply the center mark).
          So
          > when
          > > you are centering the secondary, you center the circle (which is
          > the
          > > "blot") in the Tak scope. Then you finish with the primary as you
          > > described. There is a video on the RCOS website that shows this
          and
          > > demonstrates how you collimate a RCOS RC.
          > >
          > >
          > >
          > > >On Wed, 31 Jan 2007 12:00:50 +0000, ccd-
          newastro@yahoogroups.com
          > wrote:
          > >
          > >
          >
          >____________________________________________________________________
          > ____
          > > >
          > > >5c. Re: Ritchey Chr‚tien collimation offset i don't understand
          > > > Posted by: "Randy Nulman" rj.nulman@ randy_nulman
          > > > Date: Tue Jan 30, 2007 12:52 pm ((PST))
          > > >
          > > >Hi,
          > > >First, the secondary must be totally centered, typically using
          > > >measurements of the distance from each spider vane end to the
          > tube.
          > > >(all should be equally distanced).
          > > >
          > > >Then, the tip/tilt of the secondary may be necessary to
          > align/center
          > > >the "blot" to the center of the collimation scope.
          > > >
          > > >Be sure you are looking at the "blot" (which is assymetrical)
          as
          > > >opposed to the purely round reflection of the collimation
          scope's
          > > >center. This is typically where people get confused...The
          > > >central "blot" on the secondary is NOT purely round as it's a
          dab
          > of
          > > >black on the secondary via a "marks-a-lot" scenario.
          Eventually,
          > the
          > > >pure round reflection of the collimation scope _and_ the "blot"
          > will
          > > >align/overlap closely with each other.
          > > >
          > > >Once the secondary is centered, then it's a simple matter of
          > adjusting
          > > >the primary tip/tilt until the whole "circle" is centered
          within
          > the
          > > >view of the collimation scope.
          > > >
          > > >Hope this helps,
          > > >
          > > >Randy Nulman
          > > >http://rc20.stonehenge-obs.com
          > > >
          > > >
          > >
          > > Clear Skies ..........
          > >
          > > Klaatu Barada Nikto ....
          > >
          > > Frank S(Sandy) Barnes III
          > > SBarnes@
          > > http://www.SkyImager.Com
          > >
          >
        • Frank S Barnes III
          Hi Ken, Terminology can be helpful and confusing all at the same time. Case in point... I think Randy and I are saying the same thing, but Randy s use of the
          Message 4 of 6 , Feb 1 9:33 AM
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            Hi Ken,

            Terminology can be helpful and confusing all at the same time.

            Case in point... I think Randy and I are saying the same thing,
            but Randy's use of the phrase "somewhat asymmetrical due to it's
            nature" threw me, as it's hard for me to understand how a circle can
            be asymmetrical, due to the definition :-))), My secondary happens to
            have a visually perfect circle drawn on it at the center.

            Your video is by far, IMHO, the best way to remove the confusion
            surrounding the blot - dot definitions. Thanks for putting it together.


            >On Thu, 01 Feb 2007 16:43:26 +0000, ccd-newastro@yahoogroups.com wrote:

            >________________________________________________________________________
            >
            >4e. Re: Ritchey Chrtien collimation offset i don't understand
            > Posted by: "Ken Crawford" kenc@... s_idekick
            > Date: Thu Feb 1, 2007 8:38 am ((PST))
            >
            >Sandy in the collimation vidoe, Brad and I decided to rename the
            >blot as this can be a confusing term. The video shows footage of
            >the process and you can see it very well. Sometimes the picture is
            >worth 1000 words and a Video is worth 1000 pictures :)
            >
            >http://gallery.rcopticalsystems.com/video/RCOS_Collimation_V3.wmv
            >
            >Regards,
            >
            >Ken Crawford
            >
            >--- In ccd-newastro@yahoogroups.com, "Randy Nulman" <rj.nulman@...>
            >wrote:
            >>
            >> Hi Sandy,
            >> I think we are saying the same things, but in different ways. <G>
            >>
            >> Yes, one wants to center the black "blot" (as I indicated,
            >somewhat
            >> asymmetrical due to it's nature). However there is also a
            >> black "dot" that is pure round and reflects in the center...this
            >is
            >> the reflection of the Tak Collimating scope itself, and is often
            >> confused with the "real blot" you refer to. Also, since
            >this "dot"
            >> reflection is centered, it usually will appear to "overlap" the
            >blot
            >> (or the other way around). However, even then, the "blot" is
            >still
            >> usually visible in the center.
            >>
            >> Does this make sense?
            >>
            >> Regards,
            >> Randy
            >> http://rc20.stonehenge-obs.com
            >>
            >>
            >> --- In ccd-newastro@yahoogroups.com, "Frank S Barnes III"
            >> <SBarnes@> wrote:
            >> >
            >> > Hi Randy,
            >> >
            >> > The first part of your explanation I agree with, but the
            >> second
            >> > part I differ with. On a RCOS scope, the center of the secondary
            >> mirror
            >> > will have a actual circle drawn on it that you can see in the Tak
            >> > scope. The "dab of black" on the secondary is what the black
            >magic
            >> > marker type pen leaves behind when the mirror is backed off the
            >> lathe
            >> > (the pen being inserted in the lathe to apply the center mark).
            >So
            >> when
            >> > you are centering the secondary, you center the circle (which is
            >> the
            >> > "blot") in the Tak scope. Then you finish with the primary as you
            >> > described. There is a video on the RCOS website that shows this
            >and
            >> > demonstrates how you collimate a RCOS RC.
            >> >
            >> >
            >> >
            >> > >On Wed, 31 Jan 2007 12:00:50 +0000, ccd-
            >newastro@yahoogroups.com
            >> wrote:
            >> >
            >> >
            >>
            >>____________________________________________________________________
            >> ____
            >> > >
            >> > >5c. Re: Ritchey Chr�tien collimation offset i don't understand
            >> > > Posted by: "Randy Nulman" rj.nulman@ randy_nulman
            >> > > Date: Tue Jan 30, 2007 12:52 pm ((PST))
            >> > >
            >> > >Hi,
            >> > >First, the secondary must be totally centered, typically using
            >> > >measurements of the distance from each spider vane end to the
            >> tube.
            >> > >(all should be equally distanced).
            >> > >
            >> > >Then, the tip/tilt of the secondary may be necessary to
            >> align/center
            >> > >the "blot" to the center of the collimation scope.
            >> > >
            >> > >Be sure you are looking at the "blot" (which is assymetrical)
            >as
            >> > >opposed to the purely round reflection of the collimation
            >scope's
            >> > >center. This is typically where people get confused...The
            >> > >central "blot" on the secondary is NOT purely round as it's a
            >dab
            >> of
            >> > >black on the secondary via a "marks-a-lot" scenario.
            >Eventually,
            >> the
            >> > >pure round reflection of the collimation scope _and_ the "blot"
            >> will
            >> > >align/overlap closely with each other.
            >> > >
            >> > >Once the secondary is centered, then it's a simple matter of
            >> adjusting
            >> > >the primary tip/tilt until the whole "circle" is centered
            >within
            >> the
            >> > >view of the collimation scope.
            >> > >
            >> > >Hope this helps,
            >> > >
            >> > >Randy Nulman
            >> > >http://rc20.stonehenge-obs.com

            Clear Skies ..........

            Klaatu Barada Nikto ....

            Frank S(Sandy) Barnes III
            SBarnes@...
            http://www.SkyImager.Com
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