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GSO Focuser Separation Anxiety

Discussion in 'Telescopes and Mounts' started by Mak the Night, Jan 15, 2022.

GSO Focuser Separation Anxiety

Started by Mak the Night on Jan 15, 2022 at 2:40 PM

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  1. Mak the Night

    Mak the Night Well-Known Member

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    [​IMG]

    I’ve been trying to retire my two ST80’s for several years now. I have better quality short tube refractors. The first to be modified with an aftermarket GSO focuser (as TS Optics) was the Orion ST80. This not only improved the focusing abilities it also enabled 2” accessories to be utilised. Moreover, the focuser could additionally be rotated although I didn’t normally use this option. Apparently Guan Sheng Optical are not particularly enthusiastic about the feature either:

    These focusers are rotatable, i.e., you can turn the entire focuser body/diagonal/eyepiece combination into a better observing position by loosening or tightening a large silver thumbscrew on the top of the focuser. However, please note that this is a relatively weak feature of this otherwise excellent product. We inspect every single focuser and tweak/lube it as much as we can, but the rotation is often not smooth over the entire 360-degrees and may bind in a few spots, requiring additional effort to rotate it. This is probably a minor annoyance since most people will not use this feature very often.

    Which doesn’t exactly inspire confidence. Admittedly I had some problems with the similar aftermarket GSO focuser on my ST102. This eventually led to its replacement with a different make of focuser. When the conditions are not optimal, and there is no Moon, the ST80 is good for occasional rich field observing sessions. It is robust, uncomplicated, and comparatively light to carry. To further simplify things I usually only take a couple of eyepieces out with it at most. The predominant eyepiece being a 30mm GSO SuperView. Which is agreeably lightweight in the diagonal and gives about five and a quarter arc minutes of true field.

    [​IMG]

    On the 8th of January I decided to take the Sky-Watcher ST80 out for a quick grab and go session. Due to a physical disability I often remain seated while orienting the OTA to view a specific target. There is usually no problem with my other scopes equipped with rotating focusers. As I was rotating the GSO focuser it stuck. When these focusers rotate a single thumbscrew loosens the entire focuser assembly. Allowing it to detach slightly from the flange plate which is secured into the OTA itself by three screws.

    [​IMG]

    As a consequence the more the single screw is loosened the focuser becomes slightly more detached from the plate. The OTA was pointed up at an altitude not far from the zenith. The focuser rotation was quite stubborn and I increasingly loosened the screw. So much so that to my astonishment the entire focuser, diagonal, reflex sight and 30mm SuperView came off in my hand!

    [​IMG]

    I wasn’t totally sure what had happened. I did have an idea that nothing had broken or sheared off though.

    [​IMG]

    I took the now bisected parts of the SW ST80 back to the house and replaced it with the Orion ST80. I set the Orion scope up the same way and attempted the same procedure as before. Sure enough the focuser separated from that too! Undeterred I took that inside as well and finished the session with my 72ED DS Pro.

    [​IMG]

    Later I got to analyse what went wrong. Well, apart from having a screw (too) loose, something that seems to happen to me a lot. The entire focuser is basically attached to the OTA base plate with one thumbscrew. When the OTA was more or less upright the slightly detached focuser can hang at a canted angle causing it to stick.

    [​IMG]

    Instead of rectifying this by pushing the focuser more square before attempting to rotate, I gradually loosened the thumbscrew. Luckily nothing dropped onto the ground or was damaged. I feel more confident now I understand the ins and outs of the focuser mechanism, so to speak.

    [​IMG]

    The ST80’s might not get retired quite yet after all.

    [​IMG]
     
  2. Mak the Night

    Mak the Night Well-Known Member

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    OK, it's come to my attention that there are 2mm grub screws specifically to hold the focuser into the flange plate.

    grub1.jpg

    I initially thought these were placeholder screws.

    grub2.jpg

    I've tightened them a bit and hopefully they won't bind too much.
     
  3. Orion25

    Orion25 Well-Known Member

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    I would have totally freaked out if my focuser came off in my hand! :eek::eek:
     
  4. Mak the Night

    Mak the Night Well-Known Member

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    The first time was freaky. The second time was just de rigueur lol. The moral of this tale is always check your grub screws.
     
    Orion25 likes this.

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