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RE: [sct-user] Re: Kendrick SCT Laser Collimator Questions

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  • John Mahony
    I don t know Kendrick personally. I ve never met him and have never done business with him. I first heard of his laser SCT collimator in a long section in
    Message 1 of 24 , Apr 1, 2004
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      I don't know Kendrick personally. I've never met him and have never done
      business with him. I first heard of his laser SCT collimator in a long
      section in the Mapug archives about the possibilty of using a laser to
      collimate an SCT <http://mapug.com/AstroDesigns/MAPUG/Collimn2.htm>. The
      Mapug archives contain only the high points of Mapug discussions, and this
      section ended (very uncharacteristically of Mapug) with an "Editor's note"
      that there was much more discussion of the topic not included there, and
      that the concensus was that lasers don't work to collimate an SCT.
      Kendrick's collimator was discussed extensively in that section, so I went
      to his website to see the detailed instructions. My college degrees are in
      math, but I've been involved in amateur astronomy all my life, including
      building my own scopes, which includes grinding, polishing, testing, and
      figuring the mirrors. I've learned a lot of optics along the way. I don't
      mean to sound sarcastic, but if you understand the basic idea of how a lens
      or mirror forms an image, the problem with Kendrick's method is clear.

      BTW the Mapug laser collimation section has now been updated, partly because
      I found a website selling a laser for collimating an SCT with a method that
      looks like it will work (that message is included in the archives now). But
      like other alternative methods, it will be more work, and less accurate,
      than a star test. The Mapug "Editor's note" has been updated to say
      "Editor's note: a number of members wrote to agree that the star testing
      method was superior to any of the lasers, including the Kendrick."

      I don't have anything against Kendrick personally, I just think he doesn't
      understand his laser collimator. If you look at the product index page on
      his website
      <http://www.kendrick-ai.com/astro/products.html>, he has products from many
      manufacturers, but the first section, for his own products, does not contain
      a single item with a single lens or mirror in it. I suspect someone else
      developed this product, and sold the idea to Kendrick.
      -John



      >From: geoff beneze <geoffb@...>
      >
      > >If he was selling a perpetual motion machine, would you want me to keep
      > >quiet? This product comes pretty close.
      > >For the record, I have degrees in math from Caltech and UC Berkeley, but
      >the
      > >problem with this product comes straight out of optics 101.
      > >-John
      >
      >So fundamentally, you're expressing your personal opinion, rather
      >than a professional opinion?
      >
      >Just how did this personality conflict between you and Mr. Kendrick begin?
      >--
      >Geoff Beneze
      >Tempe, AZ
      >
      >BEAST Enterprises
      >target stands - http://www.beast-enterprises.com
      >
      >NRA life Member - IDPA A00981
      >----------------------------------------
      >Every normal man must be tempted at times to spit on his hands,
      >hoist the black flag, and begin slitting throats.
      >-- H. L. Mencken
      >----------------------------------------
      >It's not what we don't know that hurts, it's what we know that ain't so.
      >--Will Rogers

      _________________________________________________________________
      Get tax tips, tools and access to IRS forms � all in one place at MSN Money!
      http://moneycentral.msn.com/tax/home.asp
    • RMOLLISE@aol.com
      In a message dated 4/1/04 2:59:18 AM Central Standard Time, ... Hi John: I m not necessarily questioning your assessment, I just want to understand. Lasers for
      Message 2 of 24 , Apr 1, 2004
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        In a message dated 4/1/04 2:59:18 AM Central Standard Time,
        jmmahony@... writes:

        > I don't know Kendrick personally. I've never met him and have never done
        > business with him. I first heard of his laser SCT collimator in a long
        > section in the Mapug archives about the possibilty of using a laser to
        > collimate an SCT <http://mapug.com/AstroDesigns/MAPUG/Collimn2.htm>. The

        Hi John:

        I'm not necessarily questioning your assessment, I just want to understand.
        Lasers for SCTs is not something I've pursued. The way the Kendrick system
        works, as I understand it, is that you achieve a collimation the "normal" way,
        insert the laser, and mark where its return appears on a target grid. Later, you
        adjust the secondary to place the laser return back on this spot to re-achieve
        the collimation. Why won't this work.

        Peace,
        Rod Mollise
        Author of _Choosing and Using a Schmidt Cassegrain Telescope_
        <http://members.aol.com/RMOLLISE/index.html>


        [Non-text portions of this message have been removed]
      • Jim Kendrick
        ... many ... Sir, I have read several of your postings now and none of them, when it comes to how my product works or who I am, have any basis of fact and are
        Message 3 of 24 , Apr 1, 2004
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          >I don't have anything against Kendrick personally, I just think he doesn't
          > understand his laser collimator. If you look at the product index page on
          > his website
          > <http://www.kendrick-ai.com/astro/products.html>, he has products from
          many
          > manufacturers, but the first section, for his own products, does not contain
          > a single item with a single lens or mirror in it. I suspect someone else
          > developed this product, and sold the idea to Kendrick.
          > -John

          Sir,

          I have read several of your postings now and none of them, when it comes to
          how my product works or who I am, have any basis of fact and are nothng
          more than your assumptions about me and the product.

          No-one sold this idea to me. I developed and designed it. I stand behind it.

          End of story.

          Jim



          Jim
        • John Mahony
          Rod, Using Kendrick s laser as a re-collimator works, approximately. Someone here checked the size of the laser spot and how much it moved when he made an
          Message 4 of 24 , Apr 1, 2004
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            Rod,
            Using Kendrick's laser as a "re-collimator" works, approximately. Someone
            here checked the size of the laser spot and how much it moved when he made
            an adjustment, and found that it took a large fraction of a turn of a
            collimation screw to move the laser spot by an amount equal to it's own
            diameter.
            But that part is only "recollimation", after you have already collimated by
            another method, and is accurate only if the other components of the optical
            system have not moved since then. But Kendrick also claims you can do a
            direct collimation with his laser- it works like this:

            Aim the scope at a paper target (supplied with the laser) about 100' away.
            Use a reticle EP to line the scope up on the bullseye pattern on the target.

            Then take out the EP and put the laser in the scope. The main beam reflects
            back to the laser, but any laser has some scattered light, and this goes
            forward to the secondary, back to the primary, and out through the
            corrector, to focus on the target.

            At this point, Kendrick says to check where the laser light is hitting the
            target (he suggests using binoculars to see the spot on the target). If
            it's not at the center, you're supposed to adjust the secondary to move it
            half way towards the center. Then go back to the view through the EP.
            Since you've adjusted the secondary, the aim will be off, so adjust the
            scope aim to move it half way towards center.

            Then repeat this process until the EP aim and laser spot are both centered.

            The obvious problem is that the laser light is going forward through the
            scope in the same way as (when using the EP) the light from the center of
            the target is going through the scope, in the "normal" direction. The
            optical paths are identical, only reversed in direction. So the only way
            the laser can miss the center of the target is if the scope aim has changed,
            or the laser is not centered the same as the EP.

            Kendrick addresses the aim problem, by including a special 2" holder for the
            laser that has a short wire (fishing leader) attached to it that you hook to
            your 2"/1.25" adapter that has your EP in it. Then when doing this process,
            when the laser is in the scope, the EP and adapter are hanging from it, and
            vice versa. That way the weight on the back of the scope is the same.

            He doesn't address the fact that a reticle EP, especially one with an X-Y
            adjustable reticle, will not necessarily have the reticle centered. Or that
            your 2"/1.25" adapter will have an arbitrary amount of clearance in it that
            results in the EP being off-center, and that the direction that it's off
            center will vary depending on the rotational orientation when you put it in
            his holder.

            But even if that problem was solved, the basic method is fundamentally
            incorrect. If the EP and its reticle, and the laser, are both centered,
            then the light path is identical in both directions. The laser _can't_ miss
            the center of the target, if that's where the scope is aimed, as viewed
            through the EP.

            I thought it might have something to do with checking at different focus
            settings, since, depending on where the field stop is in the EP, you might
            need to refocus. Then if the aim changes, that would tell you something
            about the mechanical alignment of the optical components. But the
            instructions say to refocus _if necessary_, so evidently that's not a
            significant part of his method.

            -John


            >From: RMOLLISE@...
            >
            >In a message dated 4/1/04 2:59:18 AM Central Standard Time,
            >jmmahony@... writes:
            >
            > > I don't know Kendrick personally. I've never met him and have never
            >done
            > > business with him. I first heard of his laser SCT collimator in a long
            > > section in the Mapug archives about the possibilty of using a laser to
            > > collimate an SCT <http://mapug.com/AstroDesigns/MAPUG/Collimn2.htm>.
            >The
            >
            >Hi John:
            >
            >I'm not necessarily questioning your assessment, I just want to understand.
            >Lasers for SCTs is not something I've pursued. The way the Kendrick system
            >works, as I understand it, is that you achieve a collimation the "normal"
            >way,
            >insert the laser, and mark where its return appears on a target grid.
            >Later, you
            >adjust the secondary to place the laser return back on this spot to
            >re-achieve
            >the collimation. Why won't this work.
            >
            >Peace,
            >Rod Mollise
            >Author of _Choosing and Using a Schmidt Cassegrain Telescope_
            ><http://members.aol.com/RMOLLISE/index.html>
            >

            _________________________________________________________________
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          • RMOLLISE@aol.com
            ... Hi John: Very interesting, thanks! I didn t realize there _was_ a mode other than recollimation. Peace, Rod Mollise Author of:_Choosing and Using a
            Message 5 of 24 , Apr 1, 2004
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              In a message dated 4/1/2004 7:47:36 AM Eastern Standard Time, jmmahony@... writes:

              > Rod,
              > Using Kendrick's laser as a "re-collimator" works,
              > approximately. Someone

              Hi John:

              Very interesting, thanks! I didn't realize there _was_ a mode other than "recollimation."


              Peace,
              Rod Mollise
              Author of:_Choosing and Using a Schmidt Cassegrain Telescope_
              <http://members.aol.com/RMOLLISE/index.html>
            • P T Chambers
              Hi Guys The problem I have with any laser collimator is that it ends up being another way to use a fake star at ground level. First, it will work to some
              Message 6 of 24 , Apr 1, 2004
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                Hi Guys
                The problem I have with any laser collimator is that it ends up being
                another way to use a fake star at ground level.

                First, it "will" work to some extent. John and I have had discussion
                about any method that collimates with the scope level and not at infinity.
                He pointed out correctly that when you do that (including with the laser),
                you are depending on several things in the scope not shifting or being
                manufactured correctly. Among them that the primary slider's axis is
                coincident with the mechanical/optical axis of the scope and that there is
                "no" mirror flop.

                ANY technique that collimates other than looking "up" at a star has these
                failings. A laser collimator at best, as John says, is a "recollimator"
                that is getting you back to a collimation that you had which was "good".
                There is error in the original collimation and that is compounded by the
                error of the recollimation. Not to mention that the primary is set with
                silicon rubber and can change over time.

                When I think of "critical collimation" to use for planetary or lunar
                observing, this will not satisfy the definition. An sct has a multiplying
                factor of the secondary that makes it much more sensitive to collimation
                than other stypes of scopes (maks, scts, - all the same).

                Even the position of most diagonals will change the collimation of an SCT.
                Since these things cannot be accounted for, the laser collimation has some
                inherent problems.

                I always recommend against them. Mostly because that the folks who want
                to use them are generally folks who want "easy" collimation and are a
                little intimidated by the "star" method.

                While I believe that the Kendrick is the best of the bunch,, the inherent
                problems, in my opinion, cannot be overcome.

                The distance to the target is another problem, I suspect that most folks
                use these at a few feet and that just exacerbates the issues.

                ---------
                Phil Chambers [ptchamb@...] (S.F. Bay Area - Calif. USA)

                On Thu, 1 Apr 2004 RMOLLISE@... wrote:

                > In a message dated 4/1/2004 7:47:36 AM Eastern Standard Time, jmmahony@... writes:
                >
                > > Rod,
                > > Using Kendrick's laser as a "re-collimator" works,
                > > approximately. Someone
                >
                > Hi John:
                >
                > Very interesting, thanks! I didn't realize there _was_ a mode other than "recollimation."
                >
                >
                > Peace,
                > Rod Mollise
                > Author of:_Choosing and Using a Schmidt Cassegrain Telescope_
                > <http://members.aol.com/RMOLLISE/index.html>
                >
                >
                >
                > Visit the sct-user home page at:
                >
                >
                >
                > http://members.aol.com/RMOLLISE/index4.html
                > Yahoo! Groups Links
                >
                >
                >
                >
                >
                >
              • Robert McCord
                Then repeat this process until the EP aim and laser spot are both centered. The obvious problem is that the laser light is going forward through the scope in
                Message 7 of 24 , Apr 1, 2004
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                  "Then repeat this process until the EP aim and laser spot are both
                  centered.

                  The obvious problem is that the laser light is going forward through the
                  scope in the same way as (when using the EP) the light from the center of
                  the target is going through the scope, in the "normal" direction. The
                  optical paths are identical, only reversed in direction. So the only way
                  the laser can miss the center of the target is if the scope aim has
                  changed,
                  or the laser is not centered the same as the EP."

                  John:

                  I certainly do not have the education you have but I do have a
                  question as I have been reading all these posts and am apparently
                  missing something and getting a bit confused.

                  You mention that the reason this system won't work is because the
                  light from the laser is taking the same identical path that light
                  coming in does, except of course it does so in reverse.
                  Now the area that confuses me is that since any correction done is
                  done by moving in normally very small increments the secondary, we are
                  altering the optical alignment of the scope by making these changes
                  and therefore changing the aim or light path/lasers path as well.

                  In his instructions he mentions to 1st focus the target in the center
                  of the eyepiece and ideally the lazer should be landing there
                  also(thus accurately collimated scope and sharp focus) but in a scope
                  needing collimation to some degree this laser beam would be off some
                  percentage as the secondary is minutely off the perfect optical path.
                  Not to such a degree as to miss landing on the target but enough to
                  cause precise focus to be off. My understanding is that in a perfect
                  alignment all components are in true alignment and thus everthing
                  lands in the same spot but with a minor miss alignment of the optics
                  it will appear to be in the center but all the optical paths are not
                  perfectly in alignment and thus will not converge at the same point
                  because of this small misalignment and thus they will miss convergence
                  by very timy amounts. Probably the very reason why we only have to
                  make such small adjustments in the alignment process as the mirror is
                  off only by minute amounts to begin with. The laser is just visually
                  pointing out the offset and giving us a target to use to measure and
                  refine the alignment.
                  I apologize if I am way off here. I am just pointing out my
                  understanding and certainly realize that most all of you have a far
                  better understanding and background in this than I do. So I am more
                  than anything just clearing my head and stating this here to get a
                  better understanding of where if I am confused it is.

                  Thanks
                  Bob



                  > _________________________________________________________________
                  > Find a broadband plan that fits. Great local deals on high-speed
                  Internet
                  > access.
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                • John Mahony
                  I used the article search on S&T s website to track down the article where I thought it said you were a photographer before starting your dew heater business.
                  Message 8 of 24 , Apr 1, 2004
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                    I used the article search on S&T's website to track down the article where I
                    thought it said you were a photographer before starting your dew heater
                    business. It turns out my memory was a bit fuzzy after 10 years. In a
                    review of your dew heater system in the May '94 issue, p.51 (specifically,
                    the sidebar by Roger Sinnott on p.53), it didn't say you were a
                    photographer, but "An artist...working with silk screens and sculpture".

                    As to how your method works, all I did was apply basic optics to the
                    instructions detailed on your website. Based on that, it seems quite clear
                    that it won't work. I've read the instructions and other info on your
                    website about the method several times, thinking that I must have missed
                    something, but I can't find anything that changes my impression.

                    If there is more to it, perhaps you should include it on your website, or
                    others are likely to get the same impression I have of it. I did find some
                    vague references to the mechanical axes not being the same as the optical
                    axes, which is certainly true, but that doesn't change my analysis. When
                    the scope is aimed at the target so that light from the center of the target
                    focuses at the center of the focal plane in front of the EP, then when you
                    put a light source there, it would follow the same path back, regardless of
                    mechanical inaccuracies, because those same inaccuracies affected the
                    incoming light from the target in the same way.

                    -John


                    >From: "Jim Kendrick" <jimbo_kendrick@...>
                    >Reply-To: sct-user@yahoogroups.com
                    >To: sct-user@yahoogroups.com
                    >Subject: [sct-user] Re: Kendrick SCT Laser Collimator Questions
                    >Date: Thu, 01 Apr 2004 12:09:41 -0000
                    >
                    > >I don't have anything against Kendrick personally, I just think he
                    >doesn't
                    > > understand his laser collimator. If you look at the product index page
                    >on
                    > > his website
                    > > <http://www.kendrick-ai.com/astro/products.html>, he has products from
                    >many
                    > > manufacturers, but the first section, for his own products, does not
                    >contain
                    > > a single item with a single lens or mirror in it. I suspect someone
                    >else
                    > > developed this product, and sold the idea to Kendrick.
                    > > -John
                    >
                    >Sir,
                    >
                    >I have read several of your postings now and none of them, when it comes to
                    >how my product works or who I am, have any basis of fact and are nothng
                    >more than your assumptions about me and the product.
                    >
                    >No-one sold this idea to me. I developed and designed it. I stand behind
                    >it.
                    >
                    >End of story.
                    >
                    >Jim
                    >
                    >
                    >
                    >Jim
                    >
                    >
                    >
                    >Visit the sct-user home page at:
                    >
                    >
                    >
                    >http://members.aol.com/RMOLLISE/index4.html
                    >Yahoo! Groups Links
                    >
                    >
                    >
                    >
                    >

                    _________________________________________________________________
                    Get tax tips, tools and access to IRS forms � all in one place at MSN Money!
                    http://moneycentral.msn.com/tax/home.asp
                  • geoff beneze
                    ... Evidently, then, you ve not ACTUALLY used the product? -- Geoff Beneze Tempe, AZ BEAST Enterprises target stands - http://www.beast-enterprises.com NRA
                    Message 9 of 24 , Apr 1, 2004
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                      >As to how your method works, all I did was apply basic optics to the
                      >instructions detailed on your website. Based on that, it seems quite clear
                      >that it won't work. I've read the instructions and other info on your
                      >website about the method several times, thinking that I must have missed
                      >something, but I can't find anything that changes my impression.

                      Evidently, then, you've not ACTUALLY used the product?
                      --
                      Geoff Beneze
                      Tempe, AZ

                      BEAST Enterprises
                      target stands - http://www.beast-enterprises.com

                      NRA life Member - IDPA A00981
                      ----------------------------------------
                      Every normal man must be tempted at times to spit on his hands,
                      hoist the black flag, and begin slitting throats.
                      -- H. L. Mencken
                      ----------------------------------------
                      It's not what we don't know that hurts, it's what we know that ain't so.
                      --Will Rogers
                    • Don D'Egidio
                      John, I think you are correct, if the scope is perfectly collimated. Robert, I think, has given a good explanation as to why the laser will work, if the scope
                      Message 10 of 24 , Apr 1, 2004
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                        John,

                        I think you are correct, if the scope is perfectly collimated. Robert, I think, has given a good explanation as to why the laser will work, if the scope needs to be collimated.

                        In a miscollimated scope, using a star, we center the star in the eyepiece, using whatever is necessary to guarantee the star is in the center, then defocus to see if the central obstruction is centered. If the dark spot is not centered, then the optical axis is through the center of the dark spot, wherever that happens to be located.

                        Now for the Kendrick method lets substitute the paper target for the star. We accurately center the paper target in the eyepiece. If the scope is perfectly collimated then the laser will trace the light path back to the targets center. If it is not collimated, the laser will follow the light path to where the dark spot would be if using a star at night. At that point you would repeat the Kendrick method, as many times as needed, to bring the scope into collimation.

                        I do agree with you that there are variables that can affect the collimation using the laser, such as play in the eyepiece adapter, play with the laser itself. I personally find it just as easy using a star at night.

                        Don

                        ----- Original Message -----
                        From: "John Mahony" <jmmahony@...>
                        To: <sct-user@yahoogroups.com>
                        Sent: Thursday, April 01, 2004 12:34
                        Subject: RE: [sct-user] Re: Kendrick SCT Laser Collimator Questions


                        > I used the article search on S&T's website to track down the article where I
                        > thought it said you were a photographer before starting your dew heater
                        > business. It turns out my memory was a bit fuzzy after 10 years. In a
                        > review of your dew heater system in the May '94 issue, p.51 (specifically,
                        > the sidebar by Roger Sinnott on p.53), it didn't say you were a
                        > photographer, but "An artist...working with silk screens and sculpture".
                        >
                        > As to how your method works, all I did was apply basic optics to the
                        > instructions detailed on your website. Based on that, it seems quite clear
                        > that it won't work. I've read the instructions and other info on your
                        > website about the method several times, thinking that I must have missed
                        > something, but I can't find anything that changes my impression.
                        >
                        > If there is more to it, perhaps you should include it on your website, or
                        > others are likely to get the same impression I have of it. I did find some
                        > vague references to the mechanical axes not being the same as the optical
                        > axes, which is certainly true, but that doesn't change my analysis. When
                        > the scope is aimed at the target so that light from the center of the target
                        > focuses at the center of the focal plane in front of the EP, then when you
                        > put a light source there, it would follow the same path back, regardless of
                        > mechanical inaccuracies, because those same inaccuracies affected the
                        > incoming light from the target in the same way.
                        >
                        > -John
                      • John Mahony
                        Robert and Don, I mentioned I had seen one method for using a laser to collimate an SCT that would work, and what you re talking about is headed in that
                        Message 11 of 24 , Apr 2, 2004
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                          Robert and Don,

                          I mentioned I had seen one method for using a laser to collimate an SCT that
                          would work, and what you're talking about is headed in that direction. You
                          aim the scope at a paper target about 100 feet away, and put a bright
                          artifical star at the center of the scope's focal plane, ie, at the front of
                          where an EP would normally be. That a normal star collimation pattern gets
                          projected on the paper. The only problem is the scale of the pattern. The
                          diffraction rings at 100 feet would be less than .01" apart. To see them at
                          that distance, you'd need another scope (of, not coincidentally, the exact
                          same aperture) to resolve them, unless you want to walk back and forth
                          between the scope and target after every adjustment.

                          You can make an artificial star from a laser- just put a convex lens in
                          front of it, and it causes the rays in the normally "collimated" (parallel
                          rays) laser beam to converge to a point. Beyond that, the rays diverge out
                          from that point, so it's a point source. Since a real laser has some
                          scattered rays, a pinhole aperture is usually put around the focal point,
                          but yu can try this easily at home: aim the scope at a wall or piece of
                          paper far enough to focus with an EP. The EP will act as the converging
                          lens for the laser. Since the rays converge to a point, the direction is
                          not critical, so you can just use an ordinary laser pointer, and aim it into
                          the EP. You should get a diffraction pattern on the target.

                          Kendrick's laser doesn't use a converging lens. He says that the collimated
                          beam bounces off the secondary and returns to the laser (which you can use
                          for "re-collimating" without a paper target, after the initial collimation).
                          According to the instructions, only the scattered rays are used for the
                          initial collimation (some scatter at large enough angles that they hit the
                          primary after bouncing off the secondary, so they go out the front to focus
                          on the target). You don't get a collimated laser beam when you use a lens,
                          so evidently there's no lens.

                          The instructions say that the rays that hit the target can be fosused to a
                          ball of light about 10mm across, from which it is easily determined that
                          they come from an area about 1 mm across at the laser. That would be
                          basically like trying to collimate on a planet more than twice as big as
                          Jupiter. Kendrick's instructions say to focus to get the smallest ball of
                          light. When you look at a small planet at focus in a mis-collimated scope,
                          you'll get a faint ghost image blurred slightly to one side, but most of the
                          light is at the planet. With a planet twice the size of Jupiter, the scale
                          of the blurring is tiny by comparison. And Kendrick's instructions make no
                          reference to an effect like this. He deals only with the whole ball of
                          light.

                          -John


                          >From: "Don D'Egidio" <djd521@...>
                          >Reply-To: sct-user@yahoogroups.com
                          >To: <sct-user@...>
                          >Subject: Re: [sct-user] Re: Kendrick SCT Laser Collimator Questions
                          >Date: Thu, 1 Apr 2004 15:18:32 -0500
                          >
                          >John,
                          >
                          >I think you are correct, if the scope is perfectly collimated. Robert, I
                          >think, has given a good explanation as to why the laser will work, if the
                          >scope needs to be collimated.
                          >
                          >In a miscollimated scope, using a star, we center the star in the eyepiece,
                          >using whatever is necessary to guarantee the star is in the center, then
                          >defocus to see if the central obstruction is centered. If the dark spot is
                          >not centered, then the optical axis is through the center of the dark spot,
                          >wherever that happens to be located.
                          >
                          >Now for the Kendrick method lets substitute the paper target for the star.
                          >We accurately center the paper target in the eyepiece. If the scope is
                          >perfectly collimated then the laser will trace the light path back to the
                          >targets center. If it is not collimated, the laser will follow the light
                          >path to where the dark spot would be if using a star at night. At that
                          >point you would repeat the Kendrick method, as many times as needed, to
                          >bring the scope into collimation.
                          >
                          >I do agree with you that there are variables that can affect the
                          >collimation using the laser, such as play in the eyepiece adapter, play
                          >with the laser itself. I personally find it just as easy using a star at
                          >night.
                          >
                          >Don
                          >
                          >----- Original Message -----
                          >From: "John Mahony" <jmmahony@...>
                          >To: <sct-user@yahoogroups.com>
                          >Sent: Thursday, April 01, 2004 12:34
                          >Subject: RE: [sct-user] Re: Kendrick SCT Laser Collimator Questions
                          >
                          >
                          > > I used the article search on S&T's website to track down the article
                          >where I
                          > > thought it said you were a photographer before starting your dew heater
                          > > business. It turns out my memory was a bit fuzzy after 10 years. In a
                          > > review of your dew heater system in the May '94 issue, p.51
                          >(specifically,
                          > > the sidebar by Roger Sinnott on p.53), it didn't say you were a
                          > > photographer, but "An artist...working with silk screens and sculpture".
                          > >
                          > > As to how your method works, all I did was apply basic optics to the
                          > > instructions detailed on your website. Based on that, it seems quite
                          >clear
                          > > that it won't work. I've read the instructions and other info on your
                          > > website about the method several times, thinking that I must have missed
                          > > something, but I can't find anything that changes my impression.
                          > >
                          > > If there is more to it, perhaps you should include it on your website,
                          >or
                          > > others are likely to get the same impression I have of it. I did find
                          >some
                          > > vague references to the mechanical axes not being the same as the
                          >optical
                          > > axes, which is certainly true, but that doesn't change my analysis.
                          >When
                          > > the scope is aimed at the target so that light from the center of the
                          >target
                          > > focuses at the center of the focal plane in front of the EP, then when
                          >you
                          > > put a light source there, it would follow the same path back, regardless
                          >of
                          > > mechanical inaccuracies, because those same inaccuracies affected the
                          > > incoming light from the target in the same way.
                          > >
                          > > -John
                          >
                          >
                          >
                          >Visit the sct-user home page at:
                          >
                          >
                          >
                          >http://members.aol.com/RMOLLISE/index4.html
                          >Yahoo! Groups Links
                          >
                          >
                          >
                          >
                          >

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                        • John Mahony
                          No, I haven t, and here s why: putting a laser into the system makes it sound jazzy, and I m not an expert on lasers. But the test also relies on sighting a
                          Message 12 of 24 , Apr 2, 2004
                          • 0 Attachment
                            No, I haven't, and here's why: putting a laser into the system makes it
                            sound jazzy, and I'm not an expert on lasers. But the test also relies on
                            sighting a target through an EP in a 2"/1.25" adapter. Kendrick goes to
                            great lengths to make sure that the scope aim doesn't change when you switch
                            form laser to EP. His product includes a piece of wire to attach the EP in
                            the adapter to the laser, so that when you use one or the other, the other
                            is also hanging from the end of the scope, to keep the weight even, so the
                            scope's aim doesn't change. He claims that you should be able to adjust
                            things to get the laser light spot and the scope's aim to within about 1/4"
                            on the target.

                            But in all this, you use your own reticle EP in your own 2"/1.25" adapter
                            (Kendrick's holder for the laser and EP is 2"). EP barrels and adapters are
                            typically made with one or two hundredths of an inch clearance, so when you
                            put the EP in the adapter and tighten the setscrew, it gets pushed a few
                            hundredths of an inch off-center. Putting the adapter in Kendrick's holder
                            and tightening its setscrew gives moves the adapter a few hundredths of an
                            inch off-center. By rotating the adapter in the holder, you get a few
                            hundredths of an inch variation in EP position. Then there's the reticle
                            itself, which will have similar tolerances for centering within the EP. Add
                            it all up, and you can easily get over a millimeter of variation in the
                            position of the reticle, depending on how you happen to put things together.
                            Kendrick's instructions talk about adjusting things to get the laser spot
                            and EP view within a small fraction of an inch of each other, but a 1
                            millimeter variation in the position of the reticle will cause variations of
                            that size or larger, depending on the distance to the target.

                            After all the effort he goes through to keep the scope tube aimed at the
                            same place, there is no mention of this problem. I'm not an expert on
                            lasers, but this details of this problem are covered in chapter one of any
                            optics textbook, or you can just test it at home. Put a reticle EP in a 2"
                            adapter and aim it at a terrestrial target, then check how the aim varies as
                            you rotate the EP or adapter.

                            -John


                            >From: geoff beneze <geoffb@...>
                            >Reply-To: sct-user@yahoogroups.com
                            >To: sct-user@yahoogroups.com
                            >Subject: RE: [sct-user] Re: Kendrick SCT Laser Collimator Questions
                            >Date: Thu, 1 Apr 2004 11:04:47 -0700
                            >
                            > >As to how your method works, all I did was apply basic optics to the
                            > >instructions detailed on your website. Based on that, it seems quite
                            >clear
                            > >that it won't work. I've read the instructions and other info on your
                            > >website about the method several times, thinking that I must have missed
                            > >something, but I can't find anything that changes my impression.
                            >
                            >Evidently, then, you've not ACTUALLY used the product?
                            >--
                            >Geoff Beneze
                            >Tempe, AZ
                            >
                            >BEAST Enterprises
                            >target stands - http://www.beast-enterprises.com
                            >
                            >NRA life Member - IDPA A00981
                            >----------------------------------------
                            >Every normal man must be tempted at times to spit on his hands,
                            >hoist the black flag, and begin slitting throats.
                            >-- H. L. Mencken
                            >----------------------------------------
                            >It's not what we don't know that hurts, it's what we know that ain't so.
                            >--Will Rogers
                            >
                            >
                            >
                            >
                            >Visit the sct-user home page at:
                            >
                            >
                            >
                            >http://members.aol.com/RMOLLISE/index4.html
                            >Yahoo! Groups Links
                            >
                            >
                            >
                            >
                            >

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