## Re: Re: Ritchey Chrtien collimation offset i don't understand

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• 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
Message 1 of 6 , Jan 31, 2007
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 ..........

Frank S(Sandy) Barnes III
SBarnes@...
http://www.SkyImager.Com
• Here is the link to the collimation video... http://gallery.rcopticalsystems.com/video/RCOS_Collimation_V3.wmv Hope that helps, Ken Crawford ... second ...
Message 2 of 6 , Jan 31, 2007
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
> >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 ..........
>
>
> Frank S(Sandy) Barnes III
> SBarnes@...
> http://www.SkyImager.Com
>
• 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 3 of 6 , Jan 31, 2007
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
> >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 ..........
>
>
> Frank S(Sandy) Barnes III
> SBarnes@...
> http://www.SkyImager.Com
>
• 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 4 of 6 , Feb 1, 2007
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
>> >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 ..........
>>
>>
>> Frank S(Sandy) Barnes III
>> SBarnes@...
>> http://www.SkyImager.Com
>>
>
>
• 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 5 of 6 , Feb 1, 2007
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
> > >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
> >
>
• 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 6 of 6 , Feb 1, 2007
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
>> > >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 ..........