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    Re: Sextant Scope Parallelism (was Re : SNO-T Sextant)
    From: Ken Gebhart
    Date: 2004 Aug 15, 22:00 -0500

    on 8/13/04 9:43 AM, Robert Gainer at robert_gainer_2{at}HOTMAIL.COM wrote:
    > Frank,
    > I have thought about what you said and still don?t under stand it. So I set
    > up this morning and preformed this little test. Please explain to me where I
    > went wrong in my design for the test. First I want to describe the setup for
    > this experiment. I arranged this so that I could take the shot though the
    > open door of my office. The sextant used was my Cassens & Plath. I believe
    > this instrument to be accurate. I set a stand on a tool cart and locked the
    > sextant into it. Then I measured the angle between the top of the spire and
    > the edge of the roof on a building that is about 7,000 feet away. This
    > distance was measured from the town-zoning map. All the measurements were
    > done with my 4-power scope. With the sextant still locked in position I
    > released the scope and shimmed the bottom of the post with a 1/16? thick
    > spacer. This put a noticeable misalignment in the scope. I also did this a
    > second time with the spacer at the top of the post and saw no difference in
    > the measured angle either way. Next I put the sextant at a 45-degree angle
    > and set the index arm so that the roof was an unbroken line on the horizon
    > glass. I repeated the use of shims to misalign the scope both up and down
    > relative to the frame. I still see an unbroken line on the horizon glass.
    > Unfortunately its overcast and I can?t see any other target that is further
    > away. I am sure the effect of a misalignment increases as the angle does,
    > but I expected at least a small jog in the image.
    > All the best,
    > Robert Gainer
    Unless I missed a message, it looks to me like no one replied to your
    posting.  As I read it, it seems your shimming (bottom or top of post) only
    serves to tilt the scope upwards or downwards - not left or right so as to
    be unparallel to the frame, which is what this is all about.
    Ken Gebhart

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