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

Re: [atm_free] Re: Astigmatism Images

Expand Messages
  • Tony Gondola
    Good luck John, it s all worth it in the end........... Tony ... From: John Abrahamian To: Sent: Monday, December
    Message 1 of 13 , Jan 1, 2008
    • 0 Attachment
      Good luck John, it's all worth it in the end...........

      Tony

      ----- Original Message -----
      From: "John Abrahamian" <imas1@...>
      To: <atm_free@yahoogroups.com>
      Sent: Monday, December 31, 2007 1:35 PM
      Subject: [atm_free] Re: Astigmatism Images


      > --- In atm_free@yahoogroups.com, "Tony Gondola" <acgna@...> wrote:
      >>
      >> Thanks John,
      >>
      >> I see evidence of astig in many of the new images, both from the
      > shape of
      >> the lines and from the orientation shifts. I really think that has
      > to be
      >> worked out, you've got a nasty rolled edge to repair anyway. I'll
      > bet that
      >> the diffraction ring under knife edge when nulled for the outer zone
      > is very
      >> unbalanced indicating a turned edge.
      >>
      >> Assuming the astig. isn't from strain in the glass then it has to be
      > coming
      >> from support or technique. A mirror this big and thin is going to be
      >> extremely sensitive to both. I would double check everything from the
      >> flatness of the back of the mirror to the platter and back again. If
      > all
      >> that looks fine then you'll just need to put in more time and polish
      > the
      >> defects out, being religious about frequently changing the relative
      >> orientation of all the elements. I've seen much worse then this so
      > the game
      >> is by no means lost. How much polishing time do you have in total so
      > far?
      >>
      >> Tony
      >
      >
      > I have 12-13 hours of polishing time total on the glass but wasted a
      > few hours playing around with the stig problem. The back what not flat
      > initially and I worked the back with grit and the back of a flat tool.
      > The blank is 1/16" thicker at one edge than at the other edge (180
      > degrees from it).
      >
      > I peeled up the carpet and laid a straight edge across the rubber pad
      > and do not see any light under its edge. I would've thought the 1/4"
      > foam pad and a layer of thin carpet adequate enough but perhaps I'll
      > change this too just to be sure.
      >
      > Thanks Tony, John A
      >
      >
      >
      >
      > 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
      >
    • Tony Gondola
      This is not generally done in a production environment. The distortion that s caused by a well design mirror test stand is known and an experienced optician
      Message 2 of 13 , Jan 1, 2008
      • 0 Attachment
        This is not generally done in a production environment. The distortion
        that's caused by a well design mirror test stand is known and an experienced
        optician will "test through it". Stand distortion doesn't really effect your
        ability to detect astigmatism if you test along several diameters. Astig
        rotates with the mirror while stand distortion remains fixed.

        Tony
        BigEye Optics
        http://www.digital-flight.com/thebigeye/optics.htm

        ----- Original Message -----
        From: "John Abrahamian" <imas1@...>
        To: <atm_free@yahoogroups.com>
        Sent: Monday, December 31, 2007 7:15 PM
        Subject: [atm_free] Re: Astigmatism Images


        > --- In atm_free@yahoogroups.com, "Jim Carlisle" <jim@...> wrote:
        >>
        >> If the mirror is sensitive to its environment, then you whould test it
        >> on the primary mount that it will finally be in, and in vertical and
        >> horizontal positions.
        >>
        >> Jim
        >
        >
        > Hi Jim-
        > I think you're correct. Ideally a mirror cell would be an advantage
        > yet I know professional mirror opticians use slings and stands. If I
        > make the test stand with the sling I'll have part of the cell at
        > least. I'm not sure 2" for a 25" is really thin. I think my stroke
        > technique with my machine is at fault or the table is at fault. My
        > last projects were 12.5" and 18" and I did not experience astigmatism
        > problems. But the machine was able to run full sized tools for these
        > mirrors with little trouble. The glass was Pyrex of known pedigree
        > also. My subd tool is 21.5" and is a bit tough to run smoothly on my
        > setup.
        >
        > I did replace the turntable with one that has 2 layers of wood and is
        > sealed around its edges(formica covered round tabletops) for this
        > project so that is another variable. I've not worked with BVC layered
        > glass before but as I mentioned the back was not flat before when I
        > received it. I've worked it down to what I thought would be
        > acceptable(laid straight edge on it checking for space between). I'm
        > just not sure if this work should be polishing or fine grinding now.
        > Thanks,John
        >
        >
        >
        >
        > 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.