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Re: [atm_free] Re: Help with a Large Aperture Planetary Scope

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  • jacques savard
    do you have images or diagram or picture of Pfund like hte ADA-compliant McDonald Observatory I try to find any nothing google as his limit jack 47 N 71 W
    Message 1 of 11 , Aug 1, 2008
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      do you have images or diagram or picture of Pfund

      like hte ADA-compliant McDonald Observatory

      I try to find any

      nothing

      google as his limit

      jack 47'N 71'W


      > Just my 20 millidollar's worth of opinion:
      > First, where did the f/9 come from? I made a 16" f/6 that performs
      > wonderfully on planets and the moon as well as DSO's, and it's only 8
      > feet long. I finished the mirror at about 1/18 wave RMS and it gives
      > essentially perfect imagery limited only by turbulence. As much as I
      > like long Newts, a 16" f/9 is pushing nearly all limits of practicality.
      >
      > If you had a 22" flat with a 3.5" hole at the center you could do a
      > Pfund scope - look up my writeup on the Pfund on Wikipedia. You could
      > even go to f/10 or higher, as the primary remains stationary. That
      > would give you a fixed primary mirror and viewing position, with only
      > the flat turning to steer different parts of the sky into view. The
      > ADA-compliant McDonald Observatory Wheelchair Access Telescope is a
      > two-mirror Pfund, and will use twin 18" f/8 primaries, one for north
      > viewing and one for south viewing, with a central 24" perforated feed
      > flat at the center. But unless you can make or buy your 22" steering
      > flat, the Pfund probably isn't for you.
      >
      > An open truss tube is essential. A closed tube will give you poor to
      > horrible seeing most of the time, especially with that thick a mirror
      > blank. You might consider a thinner blank, on the order of 2", to
      > reduce its thermal mass, cooldown time and boundary layer pooling.
      >
      > OK - I'm up to 21 millidollars so I'll quit. Anyone else?
      > Mike
      >
      > --- In atm_free@yahoogroups.com, "Peter" <peter@...> wrote:
      > >
      > > Hi,
      > >
      > > A good friend wants to build a 16" f/9 scope which will be intended for
      > > outstanding planetary observing. We're struggling with the
      > mechanical design
      > > of such a large scope and I wanted to pull for ideas from the ATM
      > members on
      > > this list to help us create an excellent mechanical concept. The main
      > > concern is how to maintain collimation while providing excellent
      > dampening
      > > ability to maximize image quality.
      > >
      > > The Objectives of the project are:
      > >
      > > 1) Superb planetary image quality which includes a 3" thick Pyrex
      > mirror -
      > > 50lbs
      > >
      > > 2) Solid image stability and dampening of the image at high power
      > >
      > > 3) Maintain collimation throughout the Alt movement range
      > >
      > > 4) Minimized heat currents
      > >
      > > 5) Portability in a van
      > >
      > > Some of the ideas we tossed around include:
      > >
      > > - the use of a large Aluminum tube
      > > - Surrier truss tube Newtonian such as Bob Royce's
      > > http://www.rfroyce.com/newtonian8f8_add.htm but mounted on an Alt/Az
      > mount
      > >
      > >
      > > I'd like to get some ideas how best to approach this?
      > >
      > >
      > > Thanks,
      > >
      > >
      > > Peter
      > >
      >
      >
      >
      > ------------------------------------
      >
      > Yahoo! Groups Links
      >
      >
      >
    • afja_lm139
      Try this, scroll down to my 16 . http://www.dustymars.net/IsoObservatory.htm ... for ... mechanical design ... members on ... main ... dampening ... Pyrex
      Message 2 of 11 , Aug 1, 2008
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        Try this, scroll down to my 16".
        http://www.dustymars.net/IsoObservatory.htm


        --- In atm_free@yahoogroups.com, "Peter" <peter@...> wrote:
        >
        > Hi,
        >
        > A good friend wants to build a 16" f/9 scope which will be intended
        for
        > outstanding planetary observing. We're struggling with the
        mechanical design
        > of such a large scope and I wanted to pull for ideas from the ATM
        members on
        > this list to help us create an excellent mechanical concept. The
        main
        > concern is how to maintain collimation while providing excellent
        dampening
        > ability to maximize image quality.
        >
        > The Objectives of the project are:
        >
        > 1) Superb planetary image quality which includes a 3" thick
        Pyrex mirror -
        > 50lbs
        >
        > 2) Solid image stability and dampening of the image at high power
        >
        > 3) Maintain collimation throughout the Alt movement range
        >
        > 4) Minimized heat currents
        >
        > 5) Portability in a van
        >
        > Some of the ideas we tossed around include:
        >
        > - the use of a large Aluminum tube
        > - Surrier truss tube Newtonian such as Bob Royce's
        > http://www.rfroyce.com/newtonian8f8_add.htm but mounted on an
        Alt/Az mount
        >
        >
        > I'd like to get some ideas how best to approach this?
        >
        >
        > Thanks,
        >
        >
        > Peter
        >
      • Gerald Boutin
        Lots of pictures here. http://idisk.mac.com/rwren/Public/wmwat2/index.htm -- Gerald Boutin
        Message 3 of 11 , Aug 1, 2008
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          Lots of pictures here.

          http://idisk.mac.com/rwren/Public/wmwat2/index.htm

          --
          Gerald Boutin



          --- In atm_free@yahoogroups.com, jacques savard <jacquessavard@...>
          wrote:
          >
          >
          > do you have images or diagram or picture of Pfund
          > like hte ADA-compliant McDonald Observatory
          >
          > I try to find any nothing
          >
          > google as his limit
          >
          > jack 47'N 71'W
          >
          >
        • jacques savard
          I do not know exactly waht is a ( DK Cass ) probaly a kind of casgrain but and off axis could be also good choise at F=20 jack 47 n 71 W ... to ... smaller
          Message 4 of 11 , Aug 1, 2008
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            I do not know exactly waht is a ( DK Cass ) probaly a kind of casgrain
            but and off axis could be also good choise at F=20

            jack 47'n 71'W



            > I guess I'd back up and ask: why Newtonian? A DK Cass of around say F/20
            to
            > 24 would be fairly easy to construct optically and would make a much
            smaller
            > package. You get to throw away the barlow too!
            >
            > Tony
            > BigEye Optics
            >
            > ----- Original Message -----
            > From: "Peter" <peter@...>
            > To: <atm_free@yahoogroups.com>
            > Sent: Thursday, July 31, 2008 7:11 PM
            > Subject: [atm_free] Help with a Large Aperture Planetary Scope
            >
            >
            > > Hi,
            > >
            > > A good friend wants to build a 16" f/9 scope which will be intended for
            > > outstanding planetary observing. We're struggling with the mechanical
            > > design
            > > of such a large scope and I wanted to pull for ideas from the ATM
            members
            > > on
            > > this list to help us create an excellent mechanical concept. The main
            > > concern is how to maintain collimation while providing excellent
            dampening
            > > ability to maximize image quality.
            > >
            > > The Objectives of the project are:
            > >
            > > 1) Superb planetary image quality which includes a 3" thick Pyrex
            mirror -
            > > 50lbs
            > >
            > > 2) Solid image stability and dampening of the image at high power
            > >
            > > 3) Maintain collimation throughout the Alt movement range
            > >
            > > 4) Minimized heat currents
            > >
            > > 5) Portability in a van
            > >
            > > Some of the ideas we tossed around include:
            > >
            > > - the use of a large Aluminum tube
            > > - Surrier truss tube Newtonian such as Bob Royce's
            > > http://www.rfroyce.com/newtonian8f8_add.htm but mounted on an Alt/Az
            mount
            > >
            > >
            > > I'd like to get some ideas how best to approach this?
            > >
            > >
            > > Thanks,
            > >
            > >
            > > Peter
            > >
            > >
            > > ------------------------------------
            > >
            > > Yahoo! Groups Links
            > >
            > >
            > >
            > >
            > > No virus found in this incoming message.
            > > Checked by AVG - http://www.avg.com
            > > Version: 8.0.138 / Virus Database: 270.5.10/1585 - Release Date:
            8/1/2008
            > > 6:39 AM
            > >
            > >
            > >
            >
            >
            > ------------------------------------
            >
            > Yahoo! Groups Links
            >
            >
            >
          • Tony Gondola
            I guess I d back up and ask: why Newtonian? A DK Cass of around say F/20 to 24 would be fairly easy to construct optically and would make a much smaller
            Message 5 of 11 , Aug 1, 2008
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              I guess I'd back up and ask: why Newtonian? A DK Cass of around say F/20 to
              24 would be fairly easy to construct optically and would make a much smaller
              package. You get to throw away the barlow too!

              Tony
              BigEye Optics

              ----- Original Message -----
              From: "Peter" <peter@...>
              To: <atm_free@yahoogroups.com>
              Sent: Thursday, July 31, 2008 7:11 PM
              Subject: [atm_free] Help with a Large Aperture Planetary Scope


              > Hi,
              >
              > A good friend wants to build a 16" f/9 scope which will be intended for
              > outstanding planetary observing. We're struggling with the mechanical
              > design
              > of such a large scope and I wanted to pull for ideas from the ATM members
              > on
              > this list to help us create an excellent mechanical concept. The main
              > concern is how to maintain collimation while providing excellent dampening
              > ability to maximize image quality.
              >
              > The Objectives of the project are:
              >
              > 1) Superb planetary image quality which includes a 3" thick Pyrex mirror -
              > 50lbs
              >
              > 2) Solid image stability and dampening of the image at high power
              >
              > 3) Maintain collimation throughout the Alt movement range
              >
              > 4) Minimized heat currents
              >
              > 5) Portability in a van
              >
              > Some of the ideas we tossed around include:
              >
              > - the use of a large Aluminum tube
              > - Surrier truss tube Newtonian such as Bob Royce's
              > http://www.rfroyce.com/newtonian8f8_add.htm but mounted on an Alt/Az mount
              >
              >
              > I'd like to get some ideas how best to approach this?
              >
              >
              > Thanks,
              >
              >
              > Peter
              >
              >
              > ------------------------------------
              >
              > Yahoo! Groups Links
              >
              >
              >
              >
              > No virus found in this incoming message.
              > Checked by AVG - http://www.avg.com
              > Version: 8.0.138 / Virus Database: 270.5.10/1585 - Release Date: 8/1/2008
              > 6:39 AM
              >
              >
              >
            • Tony Gondola
              ....I d also add why F/9? You re still going to need a barlow to get to the right amount of over-sampling and you don t need the large coma free field. If you
              Message 6 of 11 , Aug 1, 2008
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                ....I'd also add why F/9? You're still going to need a barlow to get to the
                right amount of over-sampling and you don't need the large coma free field.
                If you don't want to go the compound route then I'd suggest going with a
                much shorter Newtonian. Something around F4.5 would work just fine. The
                highest resolution amateur images of the moon that I know of are taken by
                Wes Higgins using a very fast Newtonians. I suspect that in this size range
                going long will only detract from the cost and performance of the system

                Tony
                BigEye Optics

                ----- Original Message -----
                From: "Tony Gondola" <acgna@...>
                To: <atm_free@yahoogroups.com>
                Sent: Friday, August 01, 2008 1:24 PM
                Subject: Re: [atm_free] Help with a Large Aperture Planetary Scope


                >I guess I'd back up and ask: why Newtonian? A DK Cass of around say F/20 to
                > 24 would be fairly easy to construct optically and would make a much
                > smaller
                > package. You get to throw away the barlow too!
                >
                > Tony
                > BigEye Optics
                >
                > ----- Original Message -----
                > From: "Peter" <peter@...>
                > To: <atm_free@yahoogroups.com>
                > Sent: Thursday, July 31, 2008 7:11 PM
                > Subject: [atm_free] Help with a Large Aperture Planetary Scope
                >
                >
                >> Hi,
                >>
                >> A good friend wants to build a 16" f/9 scope which will be intended for
                >> outstanding planetary observing. We're struggling with the mechanical
                >> design
                >> of such a large scope and I wanted to pull for ideas from the ATM members
                >> on
                >> this list to help us create an excellent mechanical concept. The main
                >> concern is how to maintain collimation while providing excellent
                >> dampening
                >> ability to maximize image quality.
                >>
                >> The Objectives of the project are:
                >>
                >> 1) Superb planetary image quality which includes a 3" thick Pyrex
                >> mirror -
                >> 50lbs
                >>
                >> 2) Solid image stability and dampening of the image at high power
                >>
                >> 3) Maintain collimation throughout the Alt movement range
                >>
                >> 4) Minimized heat currents
                >>
                >> 5) Portability in a van
                >>
                >> Some of the ideas we tossed around include:
                >>
                >> - the use of a large Aluminum tube
                >> - Surrier truss tube Newtonian such as Bob Royce's
                >> http://www.rfroyce.com/newtonian8f8_add.htm but mounted on an Alt/Az
                >> mount
                >>
                >>
                >> I'd like to get some ideas how best to approach this?
                >>
                >>
                >> Thanks,
                >>
                >>
                >> Peter
                >>
                >>
                >> ------------------------------------
                >>
                >> Yahoo! Groups Links
                >>
                >>
                >>
                >>
                >> No virus found in this incoming message.
                >> Checked by AVG - http://www.avg.com
                >> Version: 8.0.138 / Virus Database: 270.5.10/1585 - Release Date: 8/1/2008
                >> 6:39 AM
                >>
                >>
                >>
                >
                >
                > ------------------------------------
                >
                > Yahoo! Groups Links
                >
                >
                >
                >
                > No virus found in this incoming message.
                > Checked by AVG - http://www.avg.com
                > Version: 8.0.138 / Virus Database: 270.5.10/1585 - Release Date: 8/1/2008
                > 6:39 AM
                >
                >
                >
              • Mike Lockwood
                Peter, My personal experience has taught me that the ability of the mirror to cool is one of the most important variables. No matter how much you try to
                Message 7 of 11 , Aug 6, 2008
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                  Peter,

                  My personal experience has taught me that the ability of the mirror to
                  cool is one of the most important variables. No matter how much you
                  try to remove the boundary layer, it always has some effect, and the
                  best observing is always with NO fans blowing, in my experience.

                  For optimum performance, a 3" thick mirror is just too much glass, and
                  it will have a tough time cooling off on most nights. I'd recommend
                  1.4"-1.5" thick - that thickness tracks thermal changes much more
                  closely, and it is simple to build a cell for.

                  Also, I'd recommend F/5 to F/6 for the focal ratio. The instrument
                  will be much easier to deal with due to shorter tube length, and it
                  will shake less and be easier to deal with when the wind blows.

                  Robert Houdart has a 16" F/5 mirror that I made recently. It is 1.4"
                  thick, and he is having a great time using it for planetary observing.
                  Some of his comments about the mirror and its thermal characteristics
                  can be found in the third section of this page:
                  http://www.loptics.com/comments.html

                  Mike Lockwood

                  --- In atm_free@yahoogroups.com, "Peter" <peter@...> wrote:
                  > A good friend wants to build a 16" f/9 scope which will be intended
                  > for outstanding planetary observing. We're struggling with the
                  > mechanical design of such a large scope and I wanted to pull for
                  > ideas from the ATM members on this list to help us create an
                  > excellent mechanical concept. The main concern is how to maintain
                  > collimation while providing excellent dampening ability to maximize
                  > image quality.
                  >
                  > The Objectives of the project are:
                  > 1) Superb planetary image quality which includes a 3" thick Pyrex
                  > mirror - 50lbs
                  > 2) Solid image stability and dampening of the image at high power
                  > 3) Maintain collimation throughout the Alt movement range
                  > 4) Minimized heat currents
                  > 5) Portability in a van
                  > Some of the ideas we tossed around include:
                • Ed Jones
                  Peter, At F/9 one thing you could do to improve the image contrast is to make it unobstructed. You could turn it into a CHief as I did a 12.5 inch. Check out
                  Message 8 of 11 , Aug 10, 2008
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                    Peter,

                    At F/9 one thing you could do to improve the image contrast is to
                    make it unobstructed. You could turn it into a CHief as I did a 12.5
                    inch. Check out the Yahoo group "spiderless". It will be shorter than
                    a Newt, better baffled, and unobstructed. Might be what you're
                    looking for.

                    Ed Jones
                  • Gary Fuchs
                    Hello, At Stellafane ( 08) we had a chance to spend some time with Ed and his 12 CHief. Mostly on Jupiter, and even though it was low and conditions weren t
                    Message 9 of 11 , Aug 12, 2008
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                      Hello,

                      At Stellafane ('08) we had a chance to spend some time with Ed and his
                      12" CHief. Mostly on Jupiter, and even though it was low and conditions
                      weren't perfect that night - clouds moving in and out - it was still
                      the best I've seen. The first time I'd seen the moons as clearly
                      defined disks. Considerably better than our club's 26". And had a look
                      at a cluster and M31. Very nice, but Jupiter was the standout.

                      Besides that the scope is really short for a 12" f7 and even at zenith
                      would only need a small step up for ideal height folks - 5' 7" and
                      under. (That's on Ed's low tracking platform) Also didn't look too
                      complicated to build and I think could be made with various materials
                      and construction. Easy to disassemble for transport in a small car too.

                      The platform tracked nicely.

                      Gary Fuchs



                      --- In atm_free@yahoogroups.com, "Ed Jones" <solarview@...> wrote:
                      >
                      > Peter,
                      >
                      > At F/9 one thing you could do to improve the image contrast is to
                      > make it unobstructed. You could turn it into a CHief as I did a 12.5
                      > inch. Check out the Yahoo group "spiderless". It will be shorter than
                      > a Newt, better baffled, and unobstructed. Might be what you're
                      > looking for.
                      >
                      > Ed Jones
                      >
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