Loading ...
Sorry, an error occurred while loading the content.
 

Re: Grit Size Units

Expand Messages
  • Ed Jones
    All the flexed mirrors I ve looked through and admittedly not very many have had problems with astigmatism. It seems to me that it s simply trouble that you
    Message 1 of 21 , Nov 1, 2007
      All the flexed mirrors I've looked through and admittedly not very many
      have had problems with astigmatism. It seems to me that it's simply
      trouble that you don't need especially if it's a first mirror.

      Ed

      --- In atm_free@yahoogroups.com, "Richard F.L.R. Snashall" <rflrs@...>
      wrote:
      >
      > Ed Jones wrote:
      > > Don't waste your time with flexing if you want a serious telescope.
      > Not sure I know exactly what your definition of "serious" is, then...
      >
    • Richard F.L.R. Snashall
      ... That conveys much more information than the first note. Thanks.
      Message 2 of 21 , Nov 1, 2007
        Ed Jones wrote:
        > All the flexed mirrors I've looked through and admittedly not very many
        > have had problems with astigmatism. It seems to me that it's simply
        > trouble that you don't need especially if it's a first mirror.
        That conveys much more information than the first note. Thanks.
      • jacques savard
        the minimum I could said is that is a good bad side of flex analyssing very good but now like I make on any new ideal analyse the good side put on 2 colons
        Message 3 of 21 , Nov 1, 2007
        • Mitchell
          ... questions. ... than a hard ... Calculations show they can be as good as
          Message 4 of 21 , Nov 4, 2007
            --- In atm_free@yahoogroups.com, "Jerry" <wa4guu@...> wrote:
            >
            > Mitch.
            >
            >
            >
            > I am in total agreement with you, except for a few unanswered
            questions.
            > Serious questions.
            >
            >
            >
            > How do you know any have been figured as good, let alone better
            than a "hard
            > parabola"? How much better?

            Calculations show they can be as good as < 1/125 wave P-V according
            to various people I've talked to. I've only looked through one scope
            with such a mirror and the views were good. I dont know if the
            theoretical claims can be backed up equally by foucault.
            >
            > Has anyone done an FEA to determine what the theoretical nature of
            a flexed
            > sphere is? Does it really flex into a parabola or maybe some other
            curve?
            >
            > Or has someone done an interferometer measurement of flexed mirrors
            to
            > determine that in practice.
            >
            > Would the flexed mirror have a floatation edge support or a ring of
            some
            > material that would be the equivaltant of placing your hard mirror
            on a ring
            > support? If you wouldn't accept that type of support for a hard
            mirror, why
            > is it ok for a flex mirror?
            >
            > How is the flexing force alignment with the optical axis maintained
            > perfectly at various telescope altitude pointings? Wouldn't the
            weight of
            > the flex piston alone flex astigmatism into the mirror in any but
            the
            > vertical orientation?

            If it is a ring, I would imagine the pressure is evenly distributed,
            but not sure. There was a Sky & Telescope article a few years back
            aobut flexing a cheap 4 & 1/4" mirror and gettign excellent results.
            >
            > Have you made a perfect sphere? How much easier is that than
            figuring a hard
            > parabola? If the nature of a flexed sphere is some curve other than
            a
            > parabola, and there are residual errors in the sphere, how do they
            add to
            > make what kind of curve?

            Touche'


            >
            > Do you really want to have a knob to twist all night long?
            >
            > Back and forth from the focuser to the mirror. Back and forth, back
            and
            > forth. Back and forth.
            >
            > That's it. No. Back and forth, back and forth.. Well that'll do for
            now. The
            > seeing must be bad. One more twist. Looks like clouds moving in.
            I'm going
            > to pack up.

            Exactly Why I'll stick to figuring the parabola with a good old pitch
            lap (for now anyway!)

            >
            > Jerry
            >
            Mitchell
          • Tony Gondola
            I agree with that. Flexing a sphere into a parabola is a nice trick but I don t think it s a practical replacment for a well figured parabolic surface. Once
            Message 5 of 21 , Nov 4, 2007
              I agree with that. Flexing a sphere into a parabola is a nice trick but I
              don't think it's a practical replacment for a well figured parabolic
              surface. Once you get a mirror to the point of a good smooth sphere with a
              nice edge you're close to having a finished mirror. You may as well just
              figure the thing and have done with it at that point.

              Tony
              TheBigEye
              http://www.digital-flight.com/thebigeye/thebigeye.htm


              ----- Original Message -----
              From: "Mitchell" <funnybone101@...>
              To: <atm_free@yahoogroups.com>
              Sent: Sunday, November 04, 2007 1:55 PM
              Subject: [atm_free] Re: Grit Size Units


              > --- In atm_free@yahoogroups.com, "Jerry" <wa4guu@...> wrote:
              >>
              >> Mitch.
              >>
              >>
              >>
              >> I am in total agreement with you, except for a few unanswered
              > questions.
              >> Serious questions.
              >>
              >>
              >>
              >> How do you know any have been figured as good, let alone better
              > than a "hard
              >> parabola"? How much better?
              >
              > Calculations show they can be as good as < 1/125 wave P-V according
              > to various people I've talked to. I've only looked through one scope
              > with such a mirror and the views were good. I dont know if the
              > theoretical claims can be backed up equally by foucault.
              >>
              >> Has anyone done an FEA to determine what the theoretical nature of
              > a flexed
              >> sphere is? Does it really flex into a parabola or maybe some other
              > curve?
              >>
              >> Or has someone done an interferometer measurement of flexed mirrors
              > to
              >> determine that in practice.
              >>
              >> Would the flexed mirror have a floatation edge support or a ring of
              > some
              >> material that would be the equivaltant of placing your hard mirror
              > on a ring
              >> support? If you wouldn't accept that type of support for a hard
              > mirror, why
              >> is it ok for a flex mirror?
              >>
              >> How is the flexing force alignment with the optical axis maintained
              >> perfectly at various telescope altitude pointings? Wouldn't the
              > weight of
              >> the flex piston alone flex astigmatism into the mirror in any but
              > the
              >> vertical orientation?
              >
              > If it is a ring, I would imagine the pressure is evenly distributed,
              > but not sure. There was a Sky & Telescope article a few years back
              > aobut flexing a cheap 4 & 1/4" mirror and gettign excellent results.
              >>
              >> Have you made a perfect sphere? How much easier is that than
              > figuring a hard
              >> parabola? If the nature of a flexed sphere is some curve other than
              > a
              >> parabola, and there are residual errors in the sphere, how do they
              > add to
              >> make what kind of curve?
              >
              > Touche'
              >
              >
              >>
              >> Do you really want to have a knob to twist all night long?
              >>
              >> Back and forth from the focuser to the mirror. Back and forth, back
              > and
              >> forth. Back and forth.
              >>
              >> That's it. No. Back and forth, back and forth.. Well that'll do for
              > now. The
              >> seeing must be bad. One more twist. Looks like clouds moving in.
              > I'm going
              >> to pack up.
              >
              > Exactly Why I'll stick to figuring the parabola with a good old pitch
              > lap (for now anyway!)
              >
              >>
              >> Jerry
              >>
              > Mitchell
              >
              >
              >
              >
              >
              > Yahoo! Groups Links
              >
              >
              >
              >
              >
              > --
              > Internal Virus Database is out-of-date.
              > Checked by AVG Free Edition.
              > Version: 7.5.488 / Virus Database: 269.15.5/1085 - Release Date:
              > 10/22/2007 10:35 AM
              >
            Your message has been successfully submitted and would be delivered to recipients shortly.