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    mattodell's Avatar
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    Default etx-125 alignment

    Hello all,

    Many thanks for your welcome messages on the introductions page.

    I've been practicing getting the ETX-125pe set up indoors (due to cloudy conditions) so im not stumbling around out in the dark.

    would somebody be able to explain polar alignment to me and whether its worth setting the scope up this way? ive read a few articles on it now but im still confused!

    brighter skies out there today, so fingers crossed i may get out tonight! i'll keep you posted if i do.

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    blackchihuahua's Avatar
    blackchihuahua is offline White Dwarf
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    The ETX125 mount is a basic fork mount. If you just set it flat on a table or mount it flat on a tripod, it functions as an alt-az mount.

    Tilting the scope, such that the center of the azimuth axis points toward Polaris (N Hemisphere) polar aligns the scope. The alt axis (rotating the forks) then tracks in Right Ascension and the mount becomes the functional equivalent of a German Equatorial Mount (GEM).

    The easiest way to do this is to rotate the OTA such that it points straight up
    (90 degrees on the setting circle if the circle is correct). Then tilt the scope until Polaris is centered in the field of view. The amount of tilt will depend on your latitude. Be sure that the control panel on the scope base is facing West (again for Northern Hemisphere).

    As an aside, a GEM is basically an alt-az mount with the ability to easily tilt the Az axis. It looks complex and intimidating but is quite simple when analyzed.

    Polar alignment (IMHO) of an ETX works best if you're not using Goto, that is as a manual scope. Once you find the target, the motors take over and track the object which makes for much easier viewing. Don't forget to set the scope to polar mode or remove the appropriate screw from the hand controller to allow it to default to polar mode.

    My ETX90 is mounted on a tripod with an equatorial wedge which tilts it to 40 degrees (for my latitude). All I have to do to set it up for manual viewing with tracking is carry it outside and orient it such that the axis of the OTA points roughly toward Polaris and I'm all set. Takes a couple of minutes.
    The more precisely you level the scope and the more accurately you point it toward Polaris, the more accurate your tracking will be. High precision is not necessary for most manual viewing, however.

    Good Luck




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