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RE: [atm_free] Q's RE: 8" f/5 (WAS Under the radar? "Party crasher"?)

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  • Jerry
    Dave. I would suggest that you not pass up the thrill of looking at the sky with a mirror made by your own hand. Rather than asking someone else to parabolize
    Message 1 of 26 , Sep 1, 2007
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                  Dave

       

                  I would suggest that you not pass up the thrill of looking at the sky with a mirror made by your own hand. Rather than asking someone else to parabolize your mirror, go ahead and use it as is. It will probably work better than you think. I think your son will like it better if you made it yourself.

       

                  When you have the time you can parabolize it yourself. You will have a better idea just how much difference parabolization makes in performance. If you are so unhappy with the performance and can’t find the time to parabolize, then you find someone else to do it. After you have used it I don’t think you will want someone else working on it.

       

                 

                  Show us your  scope design. 

       

                  Jerry   

       

       

       

      -----Original Message---trimmed a little
      From:
      Dave  
       

      As I mentioned, I have an 8" f/5 mirror I have
      which is polished to a sphere, but is in need of parabolizing. I want to
      get the mirror finished, and build a scope for my little boy (either for
      his b-day or Christmas).

       I thought that perhaps among the
      members of a list such as this, there might be someone for whom this
      would be a 'cinch', and might be willing to finish the mirror for me,
      for a modest fee (and shipping on my "dime"). I do want to get into
      mirror making later, but right now, I want to get this scope built for
      my little boy, and at this point in time, my "time budget" just can't
      allow me to do this myself.

      Also, if anyone's interested, I have drawn up some plans for making this
      telescope, if you'd like to take a look and give me an honest critique.
      I looked at the group's file section, and I see there are photos in the
      File section, and vice versa. My drawings are simple .BMPs (done with
      MS Paint .... oooooo wow) which I would convert to JPG. ***(For any
      who might be wondering, I do have access to Adobe Illustrator, but I'm
      just getting into it, and the learning curve is a little bit steep . . .
      I'm not used to vector graphics, etc.).

       

    • Dave
      Jerry, Thanks much for your input, I appreciate it. In theory, I feel as you do, and I would like nothing better than to go down to the workshop for however
      Message 2 of 26 , Sep 1, 2007
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        Jerry,

        Thanks much for your input, I appreciate it.  In theory, I feel as you do, and I would like nothing better than to go down to the workshop for however many evenings and polish the mirror to a sphere.  But what is the learning curve for working on mirrors?  Get it?  "Curve" ?  < ducking tomatoes, eggs, etc.>    Unfortunately, as I said, time is at a premium -- an *extreme* premium -- for me . . . it has been so for awhile, and will be for some time yet.

        As for your remark  "
        Rather than asking someone else to parabolize your mirror, go ahead and use it as is. It will probably work better than you think."   . . .  I know you can get by with a sphere at around f/10, but do you really feel that way, for an f/5 mirror?

        I'll get to posting some of my scope plans tomorrow (or Monday) -- I have system (PC) problems this evening, and have to address them before I can convert my *huge* BMP graphics to JPG . . .

        Thanks again,
          Dave


        Jerry wrote:

                     Dave

                     I would suggest that you not pass up the thrill of looking at the sky with a mirror made by your own hand. Rather than asking someone else to parabolize your mirror, go ahead and use it as is. It will probably work better than you think. I think your son will like it better if you made it yourself.

                     When you have the time you can parabolize it yourself. You will have a better idea just how much difference parabolization makes in performance. If you are so unhappy with the performance and can’t find the time to parabolize, then you find someone else to do it. After you have used it I don’t think you will want someone else working on it.

                   Show us your scope design. 

                     Jerry   

         

         

         

        -----Original Message---trimmed a little
        From:
        Dave  
         

        As I mentioned, I have an 8" f/5 mirror I have
        which is polished to a sphere, but is in need of parabolizing. I want to
        get the mirror finished, and build a scope for my little boy (either for
        his b-day or Christmas).

         I thought that perhaps among the
        members of a list such as this, there might be someone for whom this
        would be a 'cinch', and might be willing to finish the mirror for me,
        for a modest fee (and shipping on my "dime"). I do want to get into
        mirror making later, but right now, I want to get this scope built for
        my little boy, and at this point in time, my "time budget" just can't
        allow me to do this myself.

        Also, if anyone's interested, I have drawn up some plans for making this
        telescope, if you'd like to take a look and give me an honest critique.
        I looked at the group's file section, and I see there are photos in the
        File section, and vice versa. My drawings are simple .BMPs (done with
        MS Paint .... oooooo wow) which I would convert to JPG. ***(For any
        who might be wondering, I do have access to Adobe Illustrator, but I'm
        just getting into it, and the learning curve is a little bit steep . . .
        I'm not used to vector graphics, etc.).

         



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      • Jerry
        Dave. I m not even saying to put a sphere on it. I m saying use it as is what ever shape it is. Don t even test it to see what shape it is. See if you can tell
        Message 3 of 26 , Sep 1, 2007
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          Dave

           

                      I’m not even saying to put a sphere on it. I’m saying use it as is what ever shape it is. Don’t even test it to see what shape it is. See if you can tell what the shape is by looking through the scope. There is no risk involved.

                      You can put the uncoated mirror as it is in the telescope and look at the Moon and Jupiter and Saturn and see if you like the view. They are bright enough that you can see them well enough to judge the resolution and whether you would be happy with that until you had time to figure it, or you can have someone else figure it..      

                      Once the mirror is polished it is useable. So use it.

                      It’s worth looking into.

           

                      Jerry

           

           

          -----Original Message-----
          From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of Dave
          Sent:
          Saturday, September 01, 2007 10:17 PM
          To: atm_free@yahoogroups.com
          Subject: [atm_free] Re: Q's RE: 8" f/5

           

          Jerry,

          Thanks much for your input, I appreciate it.  In theory, I feel as you do, and I would like nothing better than to go down to the workshop for however many evenings and polish the mirror to a sphere.  But what is the learning curve for working on mirrors?  Get it?  "Curve" ?  < ducking tomatoes, eggs, etc.>    Unfortunately, as I said, time is at a premium -- an *extreme* premium -- for me . . . it has been so for awhile, and will be for some time yet.

          As for your remark  "Rather than asking someone else to parabolize your mirror, go ahead and use it as is. It will probably work better than you think."   . . .  I know you can get by with a sphere at around f/10, but do you really feel that way, for an f/5 mirror?

          I'll get to posting some of my scope plans tomorrow (or Monday) -- I have system (PC) problems this evening, and have to address them before I can convert my *huge* BMP graphics to JPG . . .

          Thanks again,
            Dave


          Jerry wrote:

                       Dave…

                       I would suggest that you not pass up the thrill of looking at the sky with a mirror made by your own hand. Rather than asking someone else to parabolize your mirror, go ahead and use it as is. It will probably work better than you think. I think your son will like it better if you made it yourself.

                       When you have the time you can parabolize it yourself. You will have a better idea just how much difference parabolization makes in performance. If you are so unhappy with the performance and can’t find the time to parabolize, then you find someone else to do it. After you have used it I don’t think you will want someone else working on it.

                     Show us your scope design. 

                       Jerry   

           

           

           

          -----Original Message---trimmed a little
          From: Dave  
           

          As I mentioned, I have an 8" f/5 mirror I have
          which is polished to a sphere, but is in need of parabolizing. I want to
          get the mirror finished, and build a scope for my little boy (either for
          his b-day or Christmas).

           I thought that perhaps among the
          members of a list such as this, there might be someone for whom this
          would be a 'cinch', and might be willing to finish the mirror for me,
          for a modest fee (and shipping on my "dime"). I do want to get into
          mirror making later, but right now, I want to get this scope built for
          my little boy, and at this point in time, my "time budget" just can't
          allow me to do this myself.

          Also, if anyone's interested, I have drawn up some plans for making this
          telescope, if you'd like to take a look and give me an honest critique.
          I looked at the group's file section, and I see there are photos in the
          File section, and vice versa. My drawings are simple .BMPs (done with
          MS Paint .... oooooo wow) which I would convert to JPG. ***(For any
          who might be wondering, I do have access to Adobe Illustrator, but I'm
          just getting into it, and the learning curve is a little bit steep . . .
          I'm not used to vector graphics, etc.).

           



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          This message was checked by NOD32 antivirus system.
          http://www.eset. com

           

        • Dale Eason
          The main reason I post photos to the files section is that on most Yahoo groups only the owner of the picture can see a photo in the photo section in full
          Message 4 of 26 , Sep 1, 2007
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            The main reason I post photos to the files section is that on most
            Yahoo groups only the owner of the picture can see a photo in the
            photo section in full resolution. All the rest of use see a small
            image that is usually too small. At least that is they way it use to
            work.

            One reason many here would be reluctant to figure the mirror is that
            many ATM's me included have a hard time keeping the focal lenght
            within a few inch tolerance. That would be needed if you already
            have the scope built. What most do is make the mirror and then fit
            the scope to what ever focal length the mirror came out to.

            Jerry is correct that you will probably be very happy with the mirror
            as is if you have never looked through an 8 inch scope before.
            Mirrors do not have to be very good to give pleasing views of the
            Moon and Saturn.

            Two weeks ago I looked through a 12.5 inch mirror that had a strehl
            of .3 were .87 is considered diffraction limited. We were at a dark
            site and the Veil Nebula was very pretty and easily seen in that
            mirror. I had measured that mirror so I asked to measure it again.
            It was still a strehl of .3. The owner said it does a bad job on
            Mars and I can understand why.



            Dale Eason
          • brock.family
            ... From: Dale Eason To: Sent: Sunday, September 02, 2007 5:59 PM Subject: [atm_free] Re: Q s RE: 8 f/5 ... Hi
            Message 5 of 26 , Sep 2, 2007
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              ----- Original Message -----
              From: "Dale Eason" <atmpob@...>
              To: <atm_free@yahoogroups.com>
              Sent: Sunday, September 02, 2007 5:59 PM
              Subject: [atm_free] Re: Q's RE: 8" f/5


              > One reason many here would be reluctant to figure the mirror is that
              > many ATM's me included have a hard time keeping the focal lenght
              > within a few inch tolerance. That would be needed if you already
              > have the scope built. What most do is make the mirror and then fit
              > the scope to what ever focal length the mirror came out to.

              Hi Dale.
              Dave has said his mirror is polished to a sphere.
              Are you saying the focal length is likely to change a few
              inches in figuring??? Surely not.


              > Jerry is correct that you will probably be very happy with the mirror
              > as is if you have never looked through an 8 inch scope before.
              > Mirrors do not have to be very good to give pleasing views of the
              > Moon and Saturn.

              8" f/5 sphere = approx. 1.5 wave p.v., trans error 22.3, strehl 0.114
              assuming a smooth surface.
              Hmmm! I think they have to be a little better than that, no?
              I would be happy to figure it but as I live down here in New Zealand
              there must be someone a little closer interested?

              Dave Brock
            • Jerry
              I would figure the mirror for Dave if he used it first. I don t want to cheat him out of viewing the sky with a mirror made by his hand. That would also cover
              Message 6 of 26 , Sep 2, 2007
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                            I would figure the mirror for Dave if he used it first. I don’t want to cheat him out of viewing the sky with a mirror made by his hand. That would also cover the focal length issue. Parabolizing probably wouldn’t change it a 1/10” unless it needed a lot of rework. That would be the change in radius from a sphere to a parabola if all the correction were deepening the center. The change in focal length would be half that or 1/20”. The change from the RMS best fit might even be less than that.  If he made his scope for the mirror as it is now, it would be ok after figuring.

                 

                            I still recommend that he get in touch with Guy Brandenburg with the National Capital Astronomers. Dave is fairly close to where Guy is.  Guy teaches a mirror making class, and even if Dave did not want to do the work, Guy might find someone that would like to figure a mirror without the work of grinding and polishing. I think they have aluminizing capability also.

                 

                            I don’t doubt it would work better with a good figure on it. I have tested a couple of mirrors that the owners thought had to be good. Foucault testing them I had to choke back the laughter. It would be hard to make mirrors that bad by accident. Very bad can work better than you might think.

                 

                            I actually left Mars out of the target list for Dave on purpose. Except at opposition Mars can be a less than thrilling view in any telescope. If there is a dust storm it is even worse. Sometimes Mars can make anyone think their scope is broke.

                 

                Jerry

                 

                -----Original Message-----
                From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of brock.family
                Sent: Sunday, September 02, 2007 7:27 AM
                To: atm_free@yahoogroups.com
                Subject: Re: [atm_free] Re: Q's RE: 8" f/5

                 


                ----- Original Message -----
                From: "Dale Eason" <atmpob@yahoo. com>
                To: <atm_free@yahoogroup s.com>
                Sent: Sunday, September 02, 2007 5:59 PM
                Subject: [atm_free] Re: Q's RE: 8" f/5

                > One reason many here would be reluctant to figure the mirror is that
                > many ATM's me included have a hard time keeping the focal lenght
                > within a few inch tolerance. That would be needed if you already
                > have the scope built. What most do is make the mirror and then fit
                > the scope to what ever focal length the mirror came out to.

                Hi Dale.
                Dave has said his mirror is polished to a sphere.
                Are you saying the focal length is likely to change a few
                inches in figuring??? Surely not.

                > Jerry is correct that you will probably be very happy with the mirror
                > as is if you have never looked through an 8 inch scope before.
                > Mirrors do not have to be very good to give pleasing views of the
                > Moon and Saturn.

                8" f/5 sphere = approx. 1.5 wave p.v., trans error 22.3, strehl 0.114
                assuming a smooth surface.
                Hmmm! I think they have to be a little better than that, no?
                I would be happy to figure it but as I live down here in New Zealand
                there must be someone a little closer interested?

                Dave Brock

              • Richard F.L.R. Snashall
                ... Actually, an 8 f/5 paraboloid has a radius of curvature at the edge of about 80.3 ; one might think, then, that figuring would at least change it that
                Message 7 of 26 , Sep 2, 2007
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                  Jerry wrote:
                  >
                  > I would figure the mirror for Dave if he used it first. I don’t want
                  > to cheat him out of viewing the sky with a mirror made by his hand.
                  > That would also cover the focal length issue. Parabolizing probably
                  > wouldn’t change it a 1/10” unless it needed a lot of rework. That
                  > would be the change in radius from a sphere to a parabola if all the
                  > correction were deepening the center. The change in focal length would
                  > be half that or 1/20”. The change from the RMS best fit might even be
                  > less than that. If he made his scope for the mirror as it is now, it
                  > would be ok after figuring.
                  >
                  Actually, an 8" f/5 paraboloid has a radius of curvature at the
                  edge of about 80.3"; one might think, then, that figuring would
                  at least change it that much wouldn't it?
                • Jerry
                  hm^2/2R For an 8 hm^2 = 4^2 = 16 2R for the f:5 = 160 16/160 = .1 and fl change is half of that = .05 I think... I trust your math more than mine... Where
                  Message 8 of 26 , Sep 2, 2007
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                    hm^2/2R
                    For an 8" hm^2 = 4^2 = 16
                    2R for the f:5 = 160
                    16/160 = .1
                    and fl change is half of that = .05"

                    I think... I trust your math more than mine... Where did I go wrong?

                    Jerry

                    -----Original Message-----
                    From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf
                    Of Richard F.L.R. Snashall
                    Sent: Sunday, September 02, 2007 10:17 AM
                    To: atm_free@yahoogroups.com
                    Subject: Re: [atm_free] Re: Q's RE: 8" f/5

                    Jerry wrote:
                    >
                    > I would figure the mirror for Dave if he used it first. I don't want
                    > to cheat him out of viewing the sky with a mirror made by his hand.
                    > That would also cover the focal length issue. Parabolizing probably
                    > wouldn't change it a 1/10" unless it needed a lot of rework. That
                    > would be the change in radius from a sphere to a parabola if all the
                    > correction were deepening the center. The change in focal length would
                    > be half that or 1/20". The change from the RMS best fit might even be
                    > less than that. If he made his scope for the mirror as it is now, it
                    > would be ok after figuring.
                    >
                    Actually, an 8" f/5 paraboloid has a radius of curvature at the
                    edge of about 80.3"; one might think, then, that figuring would
                    at least change it that much wouldn't it?



                    Yahoo! Groups Links
                  • Richard F.L.R. Snashall
                    ... The curvature at the zone, y, for a conic is: c / sqrt^3( 1 + (1-q)*(c*y)^2 ) (My guess is that you are not using this monstrosity.) For a paraboloid, q=0:
                    Message 9 of 26 , Sep 2, 2007
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                      Jerry wrote:
                      > hm^2/2R
                      > For an 8" hm^2 = 4^2 = 16
                      > 2R for the f:5 = 160
                      > 16/160 = .1
                      > and fl change is half of that = .05"
                      >
                      > I think... I trust your math more than mine... Where did I go wrong?
                      >
                      > Jerry
                      >
                      The curvature at the zone, y, for a conic is:

                      c / sqrt^3( 1 + (1-q)*(c*y)^2 )

                      (My guess is that you are not using this monstrosity.)

                      For a paraboloid, q=0:

                      c / sqrt^3( 1 + (c*y)^2 )

                      The RoC of the zone is its inverse. I have heard that
                      "figuring" is digging out the center to change the RoC there.
                      I ignored the fact that I'm looking at it backwards -- that a
                      sphere of radius 80.3", dug out in the center, will make a
                      paraboloid with central RoC of 80".
                    • Jerry
                      I m not using that monstrosity. I was doing it in my head the easy way. What I was doing was getting the knife movement which is change in ROC of a zone (in
                      Message 10 of 26 , Sep 2, 2007
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                        I’m not using that monstrosity.  I was doing it in my head the easy way.

                         

                        What I was doing was getting the knife movement which is change in ROC of a zone (in this case the edge) relative to the ROC of the center. Since the mirror is not spherical the actual radius of the edge is not the radius of the center + the knife movement.  But the focus is still half the radius of the center.  

                         

                        Jerry

                         

                        -----Original Message-----
                        From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of Richard F.L.R. Snashall
                        Sent: Sunday, September 02, 2007 10:52 AM
                        To: atm_free@yahoogroups.com
                        Subject: Re: [atm_free] Re: Q's RE: 8" f/5

                         

                        Jerry wrote:

                        > hm^2/2R
                        > For an 8" hm^2 = 4^2 = 16
                        > 2R for the f:5 = 160
                        > 16/160 = .1
                        > and fl change is half of that = .05"
                        >
                        > I think... I trust your math more than mine... Where did I go wrong?
                        >
                        > Jerry
                        >
                        The curvature at the zone, y, for a conic is:

                        c / sqrt^3( 1 + (1-q)*(c*y)^ 2 )

                        (My guess is that you are not using this monstrosity. )

                        For a paraboloid, q=0:

                        c / sqrt^3( 1 + (c*y)^2 )

                        The RoC of the zone is its inverse. I have heard that
                        "figuring" is digging out the center to change the RoC there.
                        I ignored the fact that I'm looking at it backwards -- that a
                        sphere of radius 80.3", dug out in the center, will make a
                        paraboloid with central RoC of 80".

                      • Dave
                        Hi guys, Looks like I need to clarify a couple things or three . . . I m sorry if I didn t state things more clearly in the beginning. 1.) I have done no work
                        Message 11 of 26 , Sep 2, 2007
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                          Hi guys,

                          Looks like I need to clarify a couple things or three . . . I'm sorry if I didn't state things more clearly in the beginning.

                          1.)  I have done no work on the 8" f/5 mirror in question -- zip, zero, zilch, nada.  I bought it as-is (figured to a sphere) at an astronomy association's auction for $15.  Therefore, it has no 'sentimental' value to me, as it would if I had ground it.

                          2.)  Someone said something to the effect of  ". . . if you have never looked through an 8" scope before. . ."   Actually, I have.  I've viewed through a multitude of  8" Newtonians, and a few (ugh) SCTs (no offense meant).

                          3.)  Following up on item #2 -- I owned and used a 10" f/5.6 for many years, after which I gave it to my older son.  I have owned a 10" f/4.5 for about 11 years . . . the optics are fairly good but not great, and when I put together a "quick-and-dirty" Dob mounting, I got in a hurry (haste makes waste) and the placement of the front and back edges of the side boards got a bit "trapezoidal" such that the centers of the side bearings don't line up . . . movement in altitude is a bit interesting to say the least.

                          4.)  I appreciate the comment(s) insisting I should try parabolizing the mirror.  Indeed, I look forward into "getting my feet wet" with mirror making/finishing . . . but I cannot stress enough how tight my time budget is.  I wanted to get it finished and coated to build the scope for my little boy for Christmas, but if I do the parabolizing myself, I'll have to wait until next summer.

                          5.)  I also wasn't clear about the scope itself.  I do have basic plans made (I'll post them soon for your critique) . . . but I have not constructed it yet.  I will indeed be getting the mirror done before constructing the scope.  The fact I've been working on the plans is of little consequence . . . I can change dimensions on the graphic plans pretty easily.  One of the most important considerations I have is squeezing out the largest possible image of 100% illumination I can, without using a too-large diagonal (I think I might be able to get by with a 1.83").

                          Thanks again for all of your comments and input, I do appreciate it.

                          Sincerely,
                           Dave G.


                        • Jerry
                          Well sorry about that Dave. I guess I was the one who turned having an 8 f:5 spherical mirrror into your having made it. Heee heee, it s my fault Jerry
                          Message 12 of 26 , Sep 2, 2007
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                            Well sorry about that Dave.

                            I guess I was the one who turned having an 8" f:5 spherical mirrror
                            into your having made it.

                            Heee heee, it's my fault

                            Jerry
                          • tomofreno2000
                            Hi Dave, You can download an Excel spreadsheet here that you can use to easily explore what size diagonal mirror and focuser you need to get a fully
                            Message 13 of 26 , Sep 3, 2007
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                              Hi Dave,

                              You can download an Excel spreadsheet here that you can use to easily
                              explore what size diagonal mirror and focuser you need to get a fully
                              illuminated field of a given size for a given entrance angle of the scope:

                              http://www.oldham-optical.co.uk/

                              Just click on "Design" in the list to the left on the above home page.

                              Tom
                            • Dave
                              Hi Tom! Thanks for the info. That s a pretty nice Excel app. I do wish it were in inches, and even moreso, it would be great if I could plug in fixed (i.e.
                              Message 14 of 26 , Sep 3, 2007
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                                Hi Tom!

                                Thanks for the info.  That's a pretty nice Excel app.  I do wish it were in inches, and even moreso, it would be great if I could plug in "fixed" (i.e. unchangeable/existing)  mirror sizes. It would be much easier to use common, known mirror sizes and then lay out the rest of it, than to wonder what to do with "odd" mirror sizes.  This is especially true (to my thinking) with the folded Newt optics, since as things stand, neither the flat mirror or diagonal mirror sizes can be chosen -- they are only available as calculated results.

                                The changes I'm wishing for would be easy if I knew how to "hack" the existing spreadsheet (for which you sent a link), but I don't know how.  I work with Excel at both home and work, but I would probably spend a month or two trying to whip up my own spreadsheet app, which might or might not have the desired results.

                                Cheers,
                                 Dave G.
                                 

                                tomofreno2000 wrote:

                                Hi Dave,

                                You can download an Excel spreadsheet here that you can use to easily
                                explore what size diagonal mirror and focuser you need to get a fully
                                illuminated field of a given size for a given entrance angle of the scope:

                                http://www.oldham- optical.co. uk/

                                Just click on "Design" in the list to the left on the above home page.


                              • Jerry
                                Just ignore the mm on the spreadsheet and put all inputs in inches and output will be inches. ... From: atm_free@yahoogroups.com
                                Message 15 of 26 , Sep 3, 2007
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                                  Just ignore the “mm” on the spreadsheet and put all inputs in inches and output will be inches.

                                   

                                   

                                  -----Original Message-----
                                  From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of Dave
                                  Sent: Monday, September 03, 2007 7:36 PM
                                  To: atm_free@yahoogroups.com
                                  Subject: [atm_free] Excel app for optical calcs (WAS - Re: Q's RE: 8" f/5 - Clarifications)

                                   

                                  Hi Tom!

                                  Thanks for the info.  That's a pretty nice Excel app.  I do wish it were in inches, and even moreso, it would be great if I could plug in "fixed" (i.e. unchangeable/existing)  mirror sizes. It would be much easier to use common, known mirror sizes and then lay out the rest of it, than to wonder what to do with "odd" mirror sizes.  This is especially true (to my thinking) with the folded Newt optics, since as things stand, neither the flat mirror or diagonal mirror sizes can be chosen -- they are only available as calculated results.

                                  The changes I'm wishing for would be easy if I knew how to "hack" the existing spreadsheet (for which you sent a link), but I don't know how.  I work with Excel at both home and work, but I would probably spend a month or two trying to whip up my own spreadsheet app, which might or might not have the desired results.

                                  Cheers,
                                   Dave G.
                                   

                                  tomofreno2000 wrote:

                                  Hi Dave,

                                  You can download an Excel spreadsheet here that you can use to easily
                                  explore what size diagonal mirror and focuser you need to get a fully
                                  illuminated field of a given size for a given entrance angle of the scope:

                                  http://www.oldham- optical.co. uk/

                                  Just click on "Design" in the list to the left on the above home page.


                                   

                                • bill
                                  While we re on the subject, I have a web page on my web site (www.bill-lee.biz) that will calculate the magnitude dropoff from a sub-sized diagonal (i.e. the
                                  Message 16 of 26 , Sep 3, 2007
                                  • 0 Attachment
                                    While we're on the subject, I have a web page on my web site
                                    (www.bill-lee.biz) that will calculate the magnitude dropoff from a
                                    sub-sized diagonal (i.e. the diagonal is smaller than what is required
                                    for full illumination of the field).

                                    I also have it as a spreadsheet, but can't get to it at the moment
                                    because I have it on a external Mac hard drive, and my Mac is in the
                                    shop for repair.

                                    Bill

                                    --- In atm_free@yahoogroups.com, "tomofreno2000" <tomofreno2000@...>
                                    wrote:
                                    >
                                    > Hi Dave,
                                    >
                                    > You can download an Excel spreadsheet here that you can use to easily
                                    > explore what size diagonal mirror and focuser you need to get a fully
                                    > illuminated field of a given size for a given entrance angle of the
                                    scope:
                                    >
                                    > http://www.oldham-optical.co.uk/
                                    >
                                    > Just click on "Design" in the list to the left on the above home page.
                                    >
                                    > Tom
                                    >
                                  • Cary Chleborad
                                    Here is another diagonal calculator. http://www.wodenoptics.com/files/DiagonalCalculator.exe -C _____ From: atm_free@yahoogroups.com
                                    Message 17 of 26 , Sep 3, 2007
                                    • 0 Attachment

                                      Here is another diagonal calculator…

                                       

                                       

                                      http://www.wodenoptics.com/files/DiagonalCalculator.exe

                                       

                                       

                                      -C

                                       


                                      From: atm_free@yahoogroups.com [mailto:atm_free@yahoogroups.com] On Behalf Of bill
                                      Sent: Monday, September 03, 2007 5:27 PM
                                      To: atm_free@yahoogroups.com
                                      Subject: [atm_free] Re: Q's RE: 8" f/5 - Clarifications

                                       

                                      While we're on the subject, I have a web page on my web site
                                      (www.bill-lee. biz) that will calculate the magnitude dropoff from a
                                      sub-sized diagonal (i.e. the diagonal is smaller than what is required
                                      for full illumination of the field).

                                      I also have it as a spreadsheet, but can't get to it at the moment
                                      because I have it on a external Mac hard drive, and my Mac is in the
                                      shop for repair.

                                      Bill

                                      --- In atm_free@yahoogroup s.com, "tomofreno2000" <tomofreno2000@ ...>
                                      wrote:

                                      >
                                      > Hi Dave,
                                      >
                                      > You can download an Excel spreadsheet here that you can use to easily
                                      > explore what size diagonal mirror and focuser you need to get a fully
                                      > illuminated field of a given size for a given entrance angle of the
                                      scope:
                                      >
                                      > http://www.oldham- optical.co. uk/
                                      >
                                      > Just click on "Design" in the list to the left on the above home
                                      page.
                                      >
                                      > Tom
                                      >

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