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Thread: Beginner's scopes with EQ mounts - but without tube rings

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    Default Beginner's scopes with EQ mounts - but without tube rings



    Some lower-end scopes on equatorial (EQ) mounts come with a dovetail bar bolted directly onto the OTA. When slewing the scope across the sky using an EQ, this will result in the focuser and finder in awkward viewing positions, making the scope difficult, if not impossible, to use. Tube rings are needed so that the scope can be rotated to a more comfortable viewing position, regardless of where the scope is pointed toward the sky. With a refractor, you can at least rotate the star diagonal to a more viewable position, although the finder will still be out of whack. For a Newtonian reflector however, without tube rings, no kind of focuser adjustment will be possible.

    So in the last couple of months, I worked on putting tube rings on my 3 Celestron scopes which came with a dovetail bolted directly on the OTA.

    1) Celestron Astromaster 90EQ - very surprising that this model didn't come with rings, as it is a more higher-end beginner's scope. So I bought a pair of Antares 3.9" tube rings, shimmed the interior with black felt until it fit snugly into the body of the OTA, carefully removed the orange dovetail bar from the OTA (it is bolted from the inside with nuts, so you want to remove the front or back end of the scope to remove the nuts from the interior of the OTA), then attached the rings to the orange dovetail bar and finally, attached the rings with dovetail to the scope. Or you could leave the orange bar on the scope and buy a larger dovetail and attach the rings to that instead - the scope with original dovetail will rotate freely around the larger bar with no impediment of movement.

    Here's the scope without tube rings:

    IMG_9288.JPG

    And after the tube rings were attached:

    IMG_0104.JPGIMG_0105.JPG

    2) Celestron Astromaster 76EQ - bought a pair of Agena 5.45" tube rings, shimmed the interior of the rings with felt until there was a snug fit with the OTA, carefully removed the orange dovetail from the OTA and made sure the nuts securing the bar from the inside were carefully removed from the front end without hitting the secondary mirror as I tilted the OTA diagonally. [Warning - The casing holding the rear mirror end of the OTA is secured by nuts inside the tube, so if you unscrew and remove the mirror end, it will be almost impossible to put the mirror end back onto the OTA as before - so don't unscrew and remove the mirror end of this scope!] Attached the shimmed rings to the orange dovetail and then the OTA into the rings.

    Before pic:

    76EQ 011.jpg

    After pic:

    IMG_0322.JPG

    Since there is a limit of 5 pictures per post, I'll have to put the before and after pics of my third Celestron scope I worked on in a separate post.
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    Default Re: Beginner's scopes with EQ mounts - but without tube rings

    3) Celestron NexStar 102GT - this 102mm refractor comes on a NexStar mount, so the dovetail bar is mounted on the side of the OTA. I would like to keep the dovetail on the OTA so it could still be used on a GOTO, but the scope is better suited on a sturdy EQ, given that the NexStar GOTO mount is seriously insubstantial for this scope. I picked up a pair of 116mm tube rings from the 2015 RTMC Astronomy Expo swap meet for $10, shimmed the inside with colored felt, attached the rings to an 8" black dovetail bar that I originally purchased for my Starblast 6 OTA (to be used on a proper mount, rather than the stock tabletop), and then attached the rings with long dovetail over the shorter attached bar so that the scope rotates freely inside the rings. Then I attached the scope and rings to a sturdy Celestron Omni CG-4 EQ mount.

    Before pic:

    AZ Star Party 054.jpg

    After pic:

    IMG_0415.JPGIMG_0413.JPG


    Let me know if questions, thanks!

    Terry
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    Default Re: Beginner's scopes with EQ mounts - but without tube rings

    Very nice. Yes I hate the fiixed dovetail. Like you said, its usually fine on the refractors and cassegrains but the newts can get real awkward real quick. I have a 130 SLT newt and quickly added tube rings instead of the fixed bar. Made for much easier balance and use.
    Brett

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    Default Re: Beginner's scopes with EQ mounts - but without tube rings

    Very nice well done job!
    Clear Skies, Marco
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    Default Re: Beginner's scopes with EQ mounts - but without tube rings

    Nice post Terry, Thanks for taking the time to post it.
    SXINIAS

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