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Re: Covering mirrors when not in use in outdoor scopes

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  • Mark Christensen
    Art, The old timers had the answer to this and you referred to it yourself: Put an access hole at the bottom above the mirror with a door on it so you can put
    Message 1 of 28 , Apr 1, 2011
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      Art,
       
      The old timers had the answer to this and you referred to it
      yourself: Put an access hole at the bottom above the mirror
      with a door on it so you can put a cover right on the mirror.
       
      They really had to worry about covers with their silver coatings.
       
      Muirden describes it (briefly) in the "Amateur Astronomers
      Handbook", as does Sidwick in his book of the same name.
      Both are 1950-60 vintage.
       
      To quote Muirden: "A circular disk of cardboard, covered with
      soft cloth and padded with cotton wool, is the best protection
      for the main mirror; this can be held down by the cap that fits
      over the cell. If the tube is of the solid variety, a small door
      somewhere near the bottom is requried for the insertion and
      removal of the cover."
       
      If it was me, I'd make the hatch so the long dimension of
      the hatch was along the axis of the tube and the other
      cut was only wide enough to allow your hand and the cap
      to get in. That would reduce the impact on the strength of the
      tube. Then you would insert the cap long-ways, rotate it 90
      degrees and place it on top of the mirror.
       
      I've never had to do this but if it was me that is what I would
      try.
       
      Good luck.
       
      Mark Christensen
       
    • trulyyours05
      Mark, what s wrong with caps at the bottom and top of the OTA and a film can in the focuser? Safer. It s not an hermetic seal, but neither is the kind of cover
      Message 2 of 28 , Apr 1, 2011
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        Mark, what's wrong with caps at the bottom and top of the OTA and a film can in the focuser? Safer. It's not an hermetic seal, but neither is the kind of cover you describe. You are probably more dexterous than I am. I can see myself inserting the cover like you say and then fumbling it. Whew.

        I do use a cover that lays over the mirror on my truss tube DOB, but I have a lot of room to hold it securely.

        Al

        --- In atm_free@yahoogroups.com, "Mark Christensen" <mjcw500@...> wrote:
        >
        > Art,
        >
        > The old timers had the answer to this and you referred to it
        > yourself: Put an access hole at the bottom above the mirror
        > with a door on it so you can put a cover right on the mirror.
        >
        > They really had to worry about covers with their silver coatings.
        >
        > Muirden describes it (briefly) in the "Amateur Astronomers
        > Handbook", as does Sidwick in his book of the same name.
        > Both are 1950-60 vintage.
        >
        > To quote Muirden: "A circular disk of cardboard, covered with
        > soft cloth and padded with cotton wool, is the best protection
        > for the main mirror; this can be held down by the cap that fits
        > over the cell. If the tube is of the solid variety, a small door
        > somewhere near the bottom is requried for the insertion and
        > removal of the cover."
        >
        > If it was me, I'd make the hatch so the long dimension of
        > the hatch was along the axis of the tube and the other
        > cut was only wide enough to allow your hand and the cap
        > to get in. That would reduce the impact on the strength of the
        > tube. Then you would insert the cap long-ways, rotate it 90
        > degrees and place it on top of the mirror.
        >
        > I've never had to do this but if it was me that is what I would
        > try.
        >
        > Good luck.
        >
        > Mark Christensen
        >
      • Mark Holm
        Something inflatable? -- Mark Holm holmmarkd@gmail.com markholm@verizon.net
        Message 3 of 28 , Apr 1, 2011
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          Something inflatable?


          --
          Mark Holm
          holmmarkd@...
          markholm@...
        • sparkysquirrell
          My 8 mirror is nested down in a 10 square box, complete with a fitted top, all made of 1/2 poplar. Not perfect, but practical! Alton
          Message 4 of 28 , Apr 1, 2011
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            My 8" mirror is nested down in a 10" square box, complete with a fitted top, all made of 1/2" poplar. Not perfect, but practical!

            Alton

            --- In atm_free@yahoogroups.com, "Mark Christensen" <mjcw500@...> wrote:
            >
            > Art,
            >
            > The old timers had the answer to this and you referred to it
            > yourself: Put an access hole at the bottom above the mirror
            > with a door on it so you can put a cover right on the mirror.
            >
            > They really had to worry about covers with their silver coatings.
            >
            > Muirden describes it (briefly) in the "Amateur Astronomers
            > Handbook", as does Sidwick in his book of the same name.
            > Both are 1950-60 vintage.
            >
            > To quote Muirden: "A circular disk of cardboard, covered with
            > soft cloth and padded with cotton wool, is the best protection
            > for the main mirror; this can be held down by the cap that fits
            > over the cell. If the tube is of the solid variety, a small door
            > somewhere near the bottom is requried for the insertion and
            > removal of the cover."
            >
            > If it was me, I'd make the hatch so the long dimension of
            > the hatch was along the axis of the tube and the other
            > cut was only wide enough to allow your hand and the cap
            > to get in. That would reduce the impact on the strength of the
            > tube. Then you would insert the cap long-ways, rotate it 90
            > degrees and place it on top of the mirror.
            >
            > I've never had to do this but if it was me that is what I would
            > try.
            >
            > Good luck.
            >
            > Mark Christensen
            >
          • Francis Smith
            I have been surprised by the amount of fine dust that seems to be sucked into an otherwise tight cabinet even inside the house. Do not know if it is a change
            Message 5 of 28 , Apr 1, 2011
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              I have been surprised by the amount of fine dust that seems to be sucked into an otherwise tight cabinet even inside the house.  Do not know if it is a change in air pressure that does it, or if the dust is indeed attracted by some force such as electrostatic.   Any way, after coming through a very small crack it settles inside.   I would assume the situation would be even worse outdoors.
               
              Therefore, I think it is vital to cover the mirror to stop falling dust even through the scope is well sealed.     Gene
               


               
              On Fri, Apr 1, 2011 at 3:50 PM, trulyyours05 <algermaine@...> wrote:
               

              Mark, what's wrong with caps at the bottom and top of the OTA and a film can in the focuser? Safer. It's not an hermetic seal, but neither is the kind of cover you describe. You are probably more dexterous than I am. I can see myself inserting the cover like you say and then fumbling it. Whew.

              I do use a cover that lays over the mirror on my truss tube DOB, but I have a lot of room to hold it securely.

              Al

              --- In atm_free@yahoogroups.com, "Mark Christensen" <mjcw500@...> wrote:
              >
              > Art,
              >
              > The old timers had the answer to this and you referred to it
              > yourself: Put an access hole at the bottom above the mirror
              > with a door on it so you can put a cover right on the mirror.
              >
              > They really had to worry about covers with their silver coatings.
              >
              > Muirden describes it (briefly) in the "Amateur Astronomers
              > Handbook", as does Sidwick in his book of the same name.
              > Both are 1950-60 vintage.
              >
              > To quote Muirden: "A circular disk of cardboard, covered with
              > soft cloth and padded with cotton wool, is the best protection
              > for the main mirror; this can be held down by the cap that fits
              > over the cell. If the tube is of the solid variety, a small door
              > somewhere near the bottom is requried for the insertion and
              > removal of the cover."
              >
              > If it was me, I'd make the hatch so the long dimension of
              > the hatch was along the axis of the tube and the other
              > cut was only wide enough to allow your hand and the cap
              > to get in. That would reduce the impact on the strength of the
              > tube. Then you would insert the cap long-ways, rotate it 90
              > degrees and place it on top of the mirror.
              >
              > I've never had to do this but if it was me that is what I would
              > try.
              >
              > Good luck.
              >
              > Mark Christensen
              >


            • Mel Bartels
              Speaking of dust, there s a trick that you can use to cause dust to leap off of your mirror. Can anyone guess? Mel Bartels
              Message 6 of 28 , Apr 1, 2011
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                Speaking of dust, there’s a trick that you can use to cause dust to leap off of your mirror. Can anyone guess?

                 

                Mel Bartels

                 

              • Richard F.L.R. Snashall
                ... Electric shock therapy?? ;-)
                Message 7 of 28 , Apr 1, 2011
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                  On 4/1/2011 8:28 PM, Mel Bartels wrote:
                  >
                  >
                  > Speaking of dust, there’s a trick that you can use to cause dust to
                  > leap off of your mirror. Can anyone guess?
                  >
                  >

                  Electric shock therapy?? ;-)
                • Jerry
                  Put a bigger mirror in front of it. From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of Mel Bartels Sent: Friday, April 01, 2011 9:28
                  Message 8 of 28 , Apr 1, 2011
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                    Put a bigger mirror in front of it.

                     

                    From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of Mel Bartels
                    Sent: Friday, April 01, 2011 9:28 PM
                    To: atm_free@yahoogroups.com
                    Subject: [atm_free] dust free optics

                     




                    Speaking of dust, there’s a trick that you can use to cause dust to leap off of your mirror. Can anyone guess?

                     

                    Mel Bartels

                     




                  • trulyyours05
                    IMHO, that should work very well. Not only is the bigger mirror in the way, but if dust likes mirrors as much as it seems to, it must like bigger mirrors more,
                    Message 9 of 28 , Apr 1, 2011
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                      IMHO, that should work very well. Not only is the bigger mirror in the way, but if dust likes mirrors as much as it seems to, it must like bigger mirrors more, accounting for the leaping off the smaller mirror.

                      Al

                      --- In atm_free@yahoogroups.com, "Jerry" <wa4guu@...> wrote:
                      >
                      > Put a bigger mirror in front of it.
                      >
                      >
                      >
                      > From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf
                      > Of Mel Bartels
                      > Sent: Friday, April 01, 2011 9:28 PM
                      > To: atm_free@yahoogroups.com
                      > Subject: [atm_free] dust free optics
                      >
                      >
                      >
                      >
                      >
                      >
                      >
                      >
                      > Speaking of dust, there's a trick that you can use to cause dust to leap off
                      > of your mirror. Can anyone guess?
                      >
                      >
                      >
                      > Mel Bartels
                      >
                    • trulyyours05
                      What magnitude of negative charge is best for repelling dust Mel? And, I remember glass holding a charge very efficiently, being a very good insulator, so it
                      Message 10 of 28 , Apr 1, 2011
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                        What magnitude of negative charge is best for repelling dust Mel? And, I remember glass holding a charge very efficiently, being a very good insulator, so it can't be a very big charge or the mirror would become dangerous.

                        Al

                        --- In atm_free@yahoogroups.com, "Mel Bartels" <mbartels@...> wrote:
                        >
                        > Speaking of dust, there's a trick that you can use to cause dust to leap off
                        > of your mirror. Can anyone guess?
                        >
                        >
                        >
                        > Mel Bartels
                        >
                      • art.bianconi
                        Mel asked Can anyone guess? You Betcha. Sequester my three cats at one end of the narrow carpeted hallway. Place the mirror half way down the hallway and
                        Message 11 of 28 , Apr 1, 2011
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                          Mel asked "Can anyone guess?"

                          You Betcha.

                          Sequester my three cats at one end of the narrow carpeted hallway.

                          Place the mirror half way down the hallway and narrow it further with obstacles that force the cats to parade right past in close proximity to the mirror.

                          Then stand at the other and make noises with the can opener.

                          Spotless mirror in seconds!

                          This trick might also work in large OTA's if you can lure a squirrel inside before getting the cats!

                          I'm only kidding. . . . . .

                          I'd never do that to a squirrel!

                          Art

                           

                           

                           

                           


                          --- In atm_free@yahoogroups.com, "Mel Bartels" <mbartels@...> wrote:
                          >
                          > Speaking of dust, there's a trick that you can use to cause dust to leap off
                          > of your mirror. Can anyone guess?
                          >
                          >
                          >
                          > Mel Bartels
                          >

                        • art.bianconi
                          Mark wrote: The old timers had the answer to this and you referred to it yourself Hi Mark. Initionally I did not like the idea of cutting a hole in the side
                          Message 12 of 28 , Apr 1, 2011
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                            Mark wrote: "The old timers had the answer to this and you referred to it yourself"

                            Hi Mark.

                            Initionally I did not like the idea of cutting a hole in the side of the CAVE tube. I didn't like the structural effect on matted glass building material that was archaic from the very onset and better sueted to Chris Craft Cabin Cruisers and 1950's era Corvettes, than telescopes. Have you ever lifted one of these? It's a World War One trench morter or a municipal sewer pipe! Take your pick! That these tubes went out of existence decades before the onset of woven materials and advanced composites tells us something.

                            Yet as I read your last post it becqme apparent that there is value to be had beyond merely ease of covering the mirror from the elements.

                            For one thing, it makes the mirror dramatically easier to clean, a nightmare with the other 12.5" F-8 mirror and its 8 foot tube (another %^$#! CAVE!).

                            It also allows more rapid thermal recovery during sudden temp changes. It also allows for large volumes of forced air should it become necessary to evaporate condensation.

                            I know how to strengthen the opening with layups and add a circumferential bulkhead inside should it prove necessary. Neither is a big deal. In fact, If I cut the opening carefully with a thin slitting blade, I might even be able to attach the same closely fitted cut out as a door with a piano hinge.

                            While pondering this, I realized that the antique scope (1918?) I am restoring (with the infamous gold coating) also has an access cover, above the mirror! It slides forward about 12 inches to permit installation of the primary cell and mirror that are inserted through the opening, not from the back as we normally do. I believe there are pictures in our PHOTOS section.

                            Thanks Mark and all who offered assistence. We have a plan!

                            Stay tuned!

                            Art


                            --- In atm_free@yahoogroups.com, "Mark Christensen" <mjcw500@...> wrote:
                            >
                            > Art,
                            >
                            > The old timers had the answer to this and you referred to it
                            > yourself: Put an access hole at the bottom above the mirror
                            > with a door on it so you can put a cover right on the mirror.
                            >
                            > They really had to worry about covers with their silver coatings.
                            >
                            > Muirden describes it (briefly) in the "Amateur Astronomers
                            > Handbook", as does Sidwick in his book of the same name.
                            > Both are 1950-60 vintage.
                            >
                            > To quote Muirden: "A circular disk of cardboard, covered with
                            > soft cloth and padded with cotton wool, is the best protection
                            > for the main mirror; this can be held down by the cap that fits
                            > over the cell. If the tube is of the solid variety, a small door
                            > somewhere near the bottom is requried for the insertion and
                            > removal of the cover."
                            >
                            > If it was me, I'd make the hatch so the long dimension of
                            > the hatch was along the axis of the tube and the other
                            > cut was only wide enough to allow your hand and the cap
                            > to get in. That would reduce the impact on the strength of the
                            > tube. Then you would insert the cap long-ways, rotate it 90
                            > degrees and place it on top of the mirror.
                            >
                            > I've never had to do this but if it was me that is what I would
                            > try.
                            >
                            > Good luck.
                            >
                            > Mark Christensen
                            >

                          • art.bianconi
                            Gene wrote: I have been surprised by the amount of fine dust that seems to be sucked into an otherwise tight cabinet even inside the house. I have an
                            Message 13 of 28 , Apr 2, 2011
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                              Gene wrote: " I have been surprised by the amount of fine dust that seems to be sucked into an otherwise tight cabinet even inside the house."

                              I have an inexpensive and easy fix that is guaranteed to work. I wish I could take credit for it. . . . I can't. It was given to me by the owner of a Piper Cherokee 180, a 4 seater airplane that Piper Aircraft Corp made popular in the 60's

                              There is only one entry door on that fuselage. The cabin is low in height and even those  who stoop over had a tough time gaining entry and exiting the plane. What Piper did was to cut the door opening up and into the curved roof. They then fitted the aircraft with a clam shell shaped door that matched the opening. That worked.

                              However, the factory never could get the curved door to seal properly. The resulting wind noise added to the noise of the engine and prop,  making conversation all but impossible. So everyone got to wear noise attenuating headsets, a common problem with small A/C.

                              I knew the owner of one of these machines stored at Blairstown Airport. When he saw me land one day he beckoned me over and said "Art, get a look at this!"

                              He'd taken half inch surgical tubing and tacked it around the door edge with silicone where the gasket had been.  A plastic vacuum "T" fitting from an Auto-Parts store joined the ends of the loop and the open end of the "T" was attached to a short length of the same surgical tubing that went into the cabin and was attached to a pressure bulb. The same kind you see used on old fashioned blood pressure testers.

                              Piper wanted almost $200 for a new door gasket! This rig had set him back less than $12

                              "Come on, I'll give you a demonstration!"

                              Next thing I know we are at 3500 feet and he's rammed the throttle to full power. The wind noise was horrific. The engine noise painful and we had no headsets!  "WE DON"T NEED HEAD SETS" he shouts and shows me the pressure bulb. "CLOSE THE THUMB VALVE AND SQUEEZE THE BULB A FEW TIMES"

                              I did as instructed and within seconds the din was reduced to conversational levels in normal voices.  In fact it was much quieter than with the standard seal!  He later told me he'd used a DB meter to measure the sound levels with and without the inflated gasket and got a  40 DB reduction. THAT IS A LOT ENERGY by any standard!

                              Since then I have used that same trick on a number of aircraft that had water leaks when flying in the rain and solved leak problems that was threatening expensive radios.

                              The trick is to use latex rubber surgical tubing of appropriate diameter and to place it so that the acidic oils in your hands don't touch it.Latex is a natural rubber and in time the contact with your hands will make it brittle.

                              I cut a 1/4" diameter slot around the longerons on my two seater tandem A/C  and glued the tubing in the slot. For a piece of cabinet furniture that isn't  likely to travel at 175 knots, or for a travel case of EP's, that probably isn't needed. If you are flying commercial however and you have the EP case pressurized, don't be too surprised to hear a small pop and "hhhhhhhhhhhhhhisssssssssssssssssssss" from the overhead when the plane gets to altitude. Been there done that! Sure surprised the flight attendent! Me too!

                              By the Way, the  EP case is water tight too and floats!

                              Gene,  In the case of your cabinet at home, you'll find everything dust free. And, if for some reason, the Mrs doesn't like the looks, you can build a few old fashioned sling shots with the tubing!

                              Art

                               

                               

                               

                               

                               

                            • art.bianconi
                              Al, Here s a link that will show you how to build a Van De Graaff generator. I suspect that Guy Brandenburg can
                              Message 14 of 28 , Apr 2, 2011
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                                Al,

                                Here's a link that will show you how to build a Van De Graaff generator. I suspect that Guy Brandenburg can show you how to make one just as nice for the price of a candy bar! Science teachers love that sort of challange.

                                 http://www.eskimo.com/~billb/emotor/vdg.html

                                Mr Wizard would have loved us!  

                                Art

                                 


                                --- In atm_free@yahoogroups.com, "trulyyours05" <algermaine@...> wrote:
                                >
                                > What magnitude of negative charge is best for repelling dust Mel? And, I remember glass holding a charge very efficiently, being a very good insulator, so it can't be a very big charge or the mirror would become dangerous.
                                >
                                > Al
                                >
                                > --- In atm_free@yahoogroups.com, "Mel Bartels" mbartels@ wrote:
                                > >
                                > > Speaking of dust, there's a trick that you can use to cause dust to leap off
                                > > of your mirror. Can anyone guess?
                                > >
                                > >
                                > >
                                > > Mel Bartels
                                > >
                                >

                              • Mark Christensen
                                Al, RE: Caps and an old film can to seal the OTA. That is exactly what I do. As I said in my response to Art, I ve never felt the need to make a separate cap
                                Message 15 of 28 , Apr 2, 2011
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                                  Al,
                                   
                                  RE: Caps and an old film can to seal the OTA.
                                   
                                  That is exactly what I do. As I said in my response to Art,
                                  I've never felt the need to make a separate cap for the
                                  mirror inside the tube. But more than once I have had to
                                  clean spider poop off the mirror also, not often, but at
                                  least twice that I can recall. Ideally the OTA should be
                                  stored horizontally to keep condensation off the mirror
                                  and I don't do that either due to space constraints. So if
                                  a  spider gets in while observing it's there when I store the
                                  scope.
                                   
                                  So if Art's situation is really bad with bugs I could see
                                  why he might need to make a separate cover for the mirror.
                                   
                                  Everybody's situation is a bit different. At least I don't
                                  have to worry about Black Widows getting into my stuff
                                  here in Illinois. I had enough of that with gear stored
                                  north of Mojave, CA for three years. Nice dark skies
                                  but I had to be careful when un-stowing the equipment
                                  during a monthly business trip after storing it in a friends
                                  garage there. The little beasts got into everything.
                                   
                                  Mark C.
                                • trulyyours05
                                  LOL, that s what came to mind and that s not what will work!!! But, you can have a lot of fun with it. Fact is, the earth picks up a slight negative charge
                                  Message 16 of 28 , Apr 2, 2011
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                                    LOL, that's what came to mind and that's not what will work!!! But, you can have a lot of fun with it.

                                    Fact is, the earth picks up a slight negative charge from the solar wind (AFAIK, due to different efficiencies in capturing electrons and protons), so things on earth tend to have a negative charge. But, charge is relative in that something that has more negative charge can attract things that have less negative charge so that TV screens attract dust. But, TV screens can have a very large negative charge. I was wondering if putting a very small excess negative charge on a mirror might cause it to repel dust? Mel knows.


                                    Al

                                    --- In atm_free@yahoogroups.com, "art.bianconi" <artbianconi@...> wrote:
                                    >
                                    >
                                    > Al,
                                    >
                                    > <http://www.eskimo.com/~billb/emotor/vdg.html> Here's a link that will
                                    > show you how to build a Van De Graaff generator. I suspect that Guy
                                    > Brandenburg can show you how to make one just as nice for the price of a
                                    > candy bar! Science teachers love that sort of challange.
                                    >
                                    > <http://www.eskimo.com/~billb/emotor/vdg.html>
                                    > http://www.eskimo.com/~billb/emotor/vdg.html
                                    > <http://www.eskimo.com/~billb/emotor/vdg.html>
                                    >
                                    >
                                    > <http://www.eskimo.com/~billb/emotor/vdg.html>
                                    >
                                    >
                                    > <http://www.eskimo.com/~billb/emotor/vdg.html> Mr Wizard would have
                                    > loved us!
                                    >
                                    >
                                    >
                                    > <http://www.eskimo.com/~billb/emotor/vdg.html> Art
                                    >
                                    >
                                    >
                                    >
                                    > --- In atm_free@yahoogroups.com, "trulyyours05" <algermaine@> wrote:
                                    > >
                                    > > What magnitude of negative charge is best for repelling dust Mel? And,
                                    > I remember glass holding a charge very efficiently, being a very good
                                    > insulator, so it can't be a very big charge or the mirror would become
                                    > dangerous.
                                    > >
                                    > > Al
                                    > >
                                    > > --- In atm_free@yahoogroups.com, "Mel Bartels" mbartels@ wrote:
                                    > > >
                                    > > > Speaking of dust, there's a trick that you can use to cause dust to
                                    > leap off
                                    > > > of your mirror. Can anyone guess?
                                    > > >
                                    > > >
                                    > > >
                                    > > > Mel Bartels
                                    > > >
                                    > >
                                    >
                                  • Mel Bartels
                                    Indeed, that is the answer: touch a wire grounded to a car sized battery or similar to the aluminum coating. The dust will fly off (any dust that stuck to the
                                    Message 17 of 28 , Apr 2, 2011
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                                      Indeed, that is the answer: touch a wire grounded to a car sized battery or similar to the aluminum coating. The dust will fly off (any dust that stuck to the surface with moisture or oils won’t come off – that’ll have to be washed off). Mel Bartels

                                       

                                       

                                       

                                      From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of trulyyours05
                                      Sent: Saturday, April 02, 2011 10:17 PM
                                      To: atm_free@yahoogroups.com
                                      Subject: [atm_free] Re: dust free optics

                                       

                                       

                                      LOL, that's what came to mind and that's not what will work!!! But, you can have a lot of fun with it.

                                      Fact is, the earth picks up a slight negative charge from the solar wind (AFAIK, due to different efficiencies in capturing electrons and protons), so things on earth tend to have a negative charge. But, charge is relative in that something that has more negative charge can attract things that have less negative charge so that TV screens attract dust. But, TV screens can have a very large negative charge. I was wondering if putting a very small excess negative charge on a mirror might cause it to repel dust? Mel knows.

                                      Al

                                      --- In atm_free@yahoogroups.com, "art.bianconi" <artbianconi@...> wrote:
                                      >
                                      >
                                      > Al,
                                      >
                                      > <http://www.eskimo.com/~billb/emotor/vdg.html> Here's a link that will
                                      > show you how to build a Van De Graaff generator. I suspect that Guy
                                      > Brandenburg can show you how to make one just as nice for the price of a
                                      > candy bar! Science teachers love that sort of challange.
                                      >
                                      > <http://www.eskimo.com/~billb/emotor/vdg.html>
                                      > http://www.eskimo.com/~billb/emotor/vdg.html
                                      > <http://www.eskimo.com/~billb/emotor/vdg.html>
                                      >
                                      >
                                      > <http://www.eskimo.com/~billb/emotor/vdg.html>
                                      >
                                      >
                                      > <http://www.eskimo.com/~billb/emotor/vdg.html> Mr Wizard would have
                                      > loved us!
                                      >
                                      >
                                      >
                                      > <http://www.eskimo.com/~billb/emotor/vdg.html> Art
                                      >
                                      >
                                      >
                                      >
                                      > --- In atm_free@yahoogroups.com, "trulyyours05" <algermaine@> wrote:
                                      > >
                                      > > What magnitude of negative charge is best for repelling dust Mel? And,
                                      > I remember glass holding a charge very efficiently, being a very good
                                      > insulator, so it can't be a very big charge or the mirror would become
                                      > dangerous.
                                      > >
                                      > > Al
                                      > >
                                      > > --- In atm_free@yahoogroups.com, "Mel Bartels" mbartels@ wrote:
                                      > > >
                                      > > > Speaking of dust, there's a trick that you can use to cause dust to
                                      > leap off
                                      > > > of your mirror. Can anyone guess?
                                      > > >
                                      > > >
                                      > > >
                                      > > > Mel Bartels
                                      > > >
                                      > >
                                      >

                                    • atmpob
                                      Mel, I m confused by the directions. By grounded do you mean connected? To me grounded means a wire attached to ground. Does the battery have to be
                                      Message 18 of 28 , Apr 3, 2011
                                      • 0 Attachment
                                        Mel,

                                        I'm confused by the directions.

                                        By "grounded" do you mean connected? To me "grounded" means a wire attached to ground. Does the battery have to be attached to ground and then the ungrounded electrode connected to the coating? Which post of the battery is grounded?

                                        Will a 7.5 amp Hr sealed Lead Acid battery work? Guess I will have to try it to see. But what attributes of the car sized battery is important other than chared up? Is it the current potential that is important that makes a large battery necessary?

                                        Dale Eason

                                        --- In atm_free@yahoogroups.com, "Mel Bartels" <mbartels@...> wrote:
                                        >
                                        > Indeed, that is the answer: touch a wire grounded to a car sized battery or
                                        > similar to the aluminum coating. The dust will fly off (any dust that stuck
                                        > to the surface with moisture or oils won't come off - that'll have to be
                                        > washed off). Mel Bartels
                                      • Tim Ulmer
                                        So, if you keep a permanent negative charge on the mirror coating while observing, will that be even more effective in keeping the pesky dust from ever landing
                                        Message 19 of 28 , Apr 3, 2011
                                        • 0 Attachment
                                          So, if you keep a permanent negative charge on the mirror coating while observing, will that be even more effective in keeping the pesky dust from ever landing on your mirror in the first placer?  Maybe a 9 V on the secondary, too?
                                           
                                          Tim

                                          From: atm_free@yahoogroups.com [atm_free@yahoogroups.com] On Behalf Of Mel Bartels [mbartels@...]
                                          Sent: Saturday, April 02, 2011 11:23 PM
                                          To: atm_free@yahoogroups.com
                                          Subject: RE: [atm_free] Re: dust free optics

                                           

                                          Indeed, that is the answer: touch a wire grounded to a car sized battery or similar to the aluminum coating. The dust will fly off (any dust that stuck to the surface with moisture or oils won’t come off – that’ll have to be washed off). Mel Bartels

                                           

                                           

                                           

                                          From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of trulyyours05
                                          Sent: Saturday, April 02, 2011 10:17 PM
                                          To: atm_free@yahoogroups.com
                                          Subject: [atm_free] Re: dust free optics

                                           

                                          LOL, that's what came to mind and that's not what will work!!! But, you can have a lot of fun with it.

                                          Fact is, the earth picks up a slight negative charge from the solar wind (AFAIK, due to different efficiencies in capturing electrons and protons), so things on earth tend to have a negative charge. But, charge is relative in that something that has more negative charge can attract things that have less negative charge so that TV screens attract dust. But, TV screens can have a very large negative charge. I was wondering if putting a very small excess negative charge on a mirror might cause it to repel dust? Mel knows.

                                          Al

                                          --- In atm_free@yahoogroups.com, "art.bianconi" <artbianconi@...> wrote:
                                          >
                                          >
                                          > Al,
                                          >
                                          > <http://www.eskimo.com/~billb/emotor/vdg.html> Here's a link that will
                                          > show you how to build a Van De Graaff generator. I suspect that Guy
                                          > Brandenburg can show you how to make one just as nice for the price of a
                                          > candy bar! Science teachers love that sort of challange.
                                          >
                                          > <http://www.eskimo.com/~billb/emotor/vdg.html>
                                          > http://www.eskimo.com/~billb/emotor/vdg.html
                                          > <http://www.eskimo.com/~billb/emotor/vdg.html>
                                          >
                                          >
                                          > <http://www.eskimo.com/~billb/emotor/vdg.html>
                                          >
                                          >
                                          > <http://www.eskimo.com/~billb/emotor/vdg.html> Mr Wizard would have
                                          > loved us!
                                          >
                                          >
                                          >
                                          > <http://www.eskimo.com/~billb/emotor/vdg.html> Art
                                          >
                                          >
                                          >
                                          >
                                          > --- In atm_free@yahoogroups.com, "trulyyours05" <algermaine@> wrote:
                                          > >
                                          > > What magnitude of negative charge is best for repelling dust Mel? And,
                                          > I remember glass holding a charge very efficiently, being a very good
                                          > insulator, so it can't be a very big charge or the mirror would become
                                          > dangerous.
                                          > >
                                          > > Al
                                          > >
                                          > > --- In atm_free@yahoogroups.com, "Mel Bartels" mbartels@ wrote:
                                          > > >
                                          > > > Speaking of dust, there's a trick that you can use to cause dust to
                                          > leap off
                                          > > > of your mirror. Can anyone guess?
                                          > > >
                                          > > >
                                          > > >
                                          > > > Mel Bartels
                                          > > >
                                          > >
                                          >

                                        • Mel Bartels
                                          I ve had good luck getting clean free light dust (even sawdust) to fly off the mirror face by touching a wire with bared copper at the end to the coating at
                                          Message 20 of 28 , Apr 3, 2011
                                          • 0 Attachment

                                            I’ve had good luck getting clean free light dust (even sawdust) to fly off the mirror face by touching a wire with bared copper at the end to the coating at the mirror edge. The wire is attached to the ground terminal of my power supply for the computerized control system. Almost always it’s a deep cycle marine battery on the other side. The battery has no further ground. I’ll experiment with smaller batteries when my mirror gets dusty <smile>. Mel Bartels.

                                             

                                             

                                             

                                             

                                            From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of atmpob
                                            Sent: Sunday, April 03, 2011 9:14 AM
                                            To: atm_free@yahoogroups.com
                                            Subject: [atm_free] Re: dust free optics

                                             

                                             

                                            Mel,

                                            I'm confused by the directions.

                                            By "grounded" do you mean connected? To me "grounded" means a wire attached to ground. Does the battery have to be attached to ground and then the ungrounded electrode connected to the coating? Which post of the battery is grounded?

                                            Will a 7.5 amp Hr sealed Lead Acid battery work? Guess I will have to try it to see. But what attributes of the car sized battery is important other than chared up? Is it the current potential that is important that makes a large battery necessary?

                                            Dale Eason

                                            --- In atm_free@yahoogroups.com, "Mel Bartels" <mbartels@...> wrote:
                                            >
                                            > Indeed, that is the answer: touch a wire grounded to a car sized battery or
                                            > similar to the aluminum coating. The dust will fly off (any dust that stuck
                                            > to the surface with moisture or oils won't come off - that'll have to be
                                            > washed off). Mel Bartels

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