Re: Meridian Flip - Flop & Flexure compensation factor

Roland Christen

Remember that 1 degree of orthogonal error in the scope produces two degrees of error on the sky. Example: if the mount is pointing dead straight up and the scope is pointing 1 degree to the east due to mechanical orthogonal error, when the mount flips sides, it will point dead straight up, but now the scope will point 1 degree due west. Total pointing error is 2 degrees (twice the scope mechanical offset).

-----Original Message-----
From: Richard Moore
To: ap-gto Sent: Thu, Sep 5, 2013 1:47 am
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor

Hi Joe,

If you decide to use a shim to solve your non-orthogonality, here is the
trigonometric formula for the thickness of the shim:

(thickness of the shim)  equals  (distance between fore and aft connection to
the male D plate)  times
   ( cosine( arc seconds that the target moves after the meridian flip ))

The scientific calculator on my computer required me to convert the arc seconds
to arc degrees by dividing by 3600.

I then went to the hardware store with my micrometer and measured their brass
sheet stock until I found the right combination.

Sketch the geometry of the scope and camera on both sides of the meridian to
find whether to shim fore or aft, (or just trial and error),

Good Luck


----- Original Message -----
From: Joseph Zeglinski
To: ap-gto@...
Sent: 9/4/2013 18:03:29
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor

Thanks for the confirmation, Rolando.

    Spent all last night using Pempro-2 to adjust the alignment, but as it
turned out -  much to my regret - there wasn’t much to tweak to what I had done
initially with my original manual drift alignment. The alignment seemed to be
pretty decent already. Sky testing clouded out tonight, to see if it made any
difference, or if the target comes closer to FOV on both sides of the pier.

    As for shimming, I am a little dubious about trying to slip a thin piece of
copper under that hefty 75 lb scope. Not much room under the D-plate, or even
knowing which end – fore or aft. Are there procedures to determine which way the
OTA is tilted in its saddle, and roughly how thick a shim might be needed, and
where to place the brass shim? Sure would be a neat feature to add to Pempro, or
any other alignment software

    The software modeling approach might be the easiest.


From: chris1011@...
Sent: Wednesday, September 04, 2013 3:36 PM
To: ap-gto@...
Subject: Re: [ap-gto] Meridian Flip - Flop & Flexure compensation factor

What you have is classic non-orthogonality. The scope optics point slightly
different direction from the scope mechanical axis. Although it always looks
like a mount problem, it is really simply an inherent offset in the scope
itself. You can try shimming the mounting plate, or you can use one of the
software programs to compensate for this offset.


[Non-text portions of this message have been removed]


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