AE 12″ Newt/Cass telescope -Mirror separation

Forums Telescopes AE 12″ Newt/Cass telescope -Mirror separation

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    Eric Watkins

    A little while ago I purchased an AE 12″ F:5/20 Cassegrain telescope with an 3″ diameter secondary mirror which I plan to use for lunar and planetary imaging.

    The  owner sold it in the Newtonian mode and had forgotten the primary-secondary  optimum mirror separation for this particular telescope.
    I plan to renovate the OTA by using carbon fiber tubes to replace the original  6 aluminum tubes that form  the skeleton OTA. Also I will  add  a modern focuser.
    Does any member still have a similar telescope or can recall the mirror separations?

    I have contacted Martin Mobberley who once had a 14″  similar telescope. However, the separation came already set upon delivery and needed no additional  thought.
    As Martin suggested I could plate solve images to determine the plate scale making any necessary adjustments until I obtain the expected F:20 focal length.

    Hopefully, any owners past or present may already have the information to give me a head start.

    Best wishes,

    Eric Watkins


    with further assistance from Martin and ES Reid ( maker of mirrors for AE) together with using the Cassegrain equations and comparing to the existing Newtonian set up the problem has been resolved.  Answer being 45″  with a little tweaking when compared to images if necessary.

    Thanks if you took some time to give this your attention.



    Jeremy Shears

    Sounds a really interesting and worthwhile project, Eric. I hope you’ll document it and share how you get on with members.

    Good luck!


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