[ATM] CG Precision

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

I have started to try to design a two-configuration Petzval.  The
baseline is a low-cost design, where the smaller doublet is cemented:

    http://users.rcn.com/rflrs/Ptz05-02x.atm
    http://users.rcn.com/rflrs/Ptz05-02x.len
    http://users.rcn.com/rflrs/Ptz05-02x.txt
    http://users.rcn.com/rflrs/Ptz05-02x.zmx

Against that, I have tried to design a high-cost group that is used
as a replacement for the smaller doublet:

    http://users.rcn.com/rflrs/Ptz05-20x.atm
    http://users.rcn.com/rflrs/Ptz05-20x.len
    http://users.rcn.com/rflrs/Ptz05-20x.txt
    http://users.rcn.com/rflrs/Ptz05-20x.zmx

The point here is to make the second telescope apochromatic and at
least reasonably corrected.  (This particular one has a Visual
Strehl of 0.964.)

I have roughly eyeballed the positioning of the second design group
to have a common center of gravity with the first design group.
This is shown in the overlay picture:

    http://users.rcn.com/rflrs/Ptz05-20x.jpg

Do you think this is a critical operation, and, if it really needs to
be precise, does someone out there maybe have an Excel spreadsheet
or something that can help me calculate the actual CGs of the groups?

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