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Nightspore

Rotating Focuser Bad Vibes

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Nightspore

Around 18 months ago I bought a Sky-Watcher ST102 StarTravel as a rich field grab'n'go scope

 

11SwKqu.jpg

 

I never used it as stock and replaced its original focuser with a heave duty TS Optics (GSO) Crayford-rail like on my modified ST80's.

 

PV7NC40.jpg

6dLr6GT.jpg

 

This was fine and worked really well after I sorted out all of the back or in-focusing problems and suitable accessories etc. 

 

nkWylEI.jpg

 

However, this year I started experimenting with actually rotating the focuser. I'm physically disabled so this function can make life a lot easier. After a while I noticed that the focuser was often less smooth at certain times and sometimes distinctly rough to turn almost as if something internally was 'grinding' and causing friction. Even Guan Sheng Optical are surprisingly candid about the rotation capabilities of their focusers.

 

4. 360-degree Rotation
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. ~ Manufacturer's description (my bold and underlining).

 

Trouble is, apparently I'm not 'most people' and now find the feature indispensable. 

 

sOvgdOw.png

 

So I've ordered a Sky-Watcher (Synta?) equivalent. These now have holes for a finder shoe and were the type I originally wanted. If this fails I'm going to have to go Moonlite lol.

 

Has anyone else had a similar experience with the GSO focusers?

 

 

 

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Nightspore
1 hour ago, Ron Clarke said:

Sorry, fitted a Moonlite to my ED80 Pro!!

Yeah, definitely a contender. If the Synta one doesn't work out I can see me getting a Moonlite for the ST102.

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Nightspore

Yeah, definitely a contender. If the Synta one doesn't work out I can see me getting a Moonlite for the ST102. There could be something wrong with the GSO anyway. I noticed the uneven rotation early on, but the 'grinding' happens with the focuser knob itself and I can even feel it through the fine focus knob. It does seem related to the rotation angle but often it seems just as smooth as it always did. I think that it is related to the way the mechanism works. The rotating bit seems to sag somewhat when the rotation knob is loosened and I don't think it always connects back properly at certain angles when re-tightened. Possibly some form of deficient clutch plate. It's interesting that GSO are quite open about it being a weakness. I was told by someone that they'd switched a GSO to a Synta as it performed better, although they didn't elaborate on the reason.

 

I can understand putting a Moonlite on an ED80 but the ST102 doesn't have such a good quality doublet. It is very convenient as a scope however as it is the biggest refractor I can safely mount on the AZ5. 

 

So if the Synta turns out to be a turkey I don't mind splashing the cash for a Moonlite. 

Edited by Nightspore

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Nightspore

cTdnZdB.jpg

 

The Sky-Watcher focuser seems to work well so far.

 

Hp71ma0.jpg

 

It is much smoother to rotate and seems more like the one on my 102mm Starwave. Allen keys rather than three screws hold it in the optical tube.

 

RraLoHo.jpg

 

It is longer than the GSO so there have been in-focusing issues with three or four EP's, although this can be remedied by changing the diagonal.

 

qwOEYxs.jpg

 

There's only one screw holding the 2" diagonal, unlike two on the GSO, although it seems substantial. All I need now is a lack of clouds!

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Nightspore

iQ9x6nS.jpg

 

I managed to get out last night. At 23:00 it wasn't looking very good but I set up the ST102 anyway.

 

sXuBsWQ.jpg

 

Initially I only took out two eyepieces, a Baader Hyperion Zoom and a 36mm Baader Hyperion Aspheric.

 

Ulg9Bz0.jpg

 

I thought it would be an opportunity to test the new focuser in the field (or my lawn lol). It cleared after midnight and I got well over an hour before the clouds came back. Before I went back to get a 5x Barlow to look at Jupiter a bit I saw a lot of open clusters in the south east. Highlights were the Wild Duck and the Summer Beehive.

 

tWLKrTj.png

 

The icing on the cake was a low M31 though.

 

poqOg8s.png

 

The focuser is definitely an improvement on the GSO.

 

 

 

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philjay

Yep, thats a threaded hole, so you can either put another thumb screw in there or swap the existing one to it.

Rotating focusers. Most focusers use 3 screws 120 deg apart on the body, one being the lock screw the others grub screws, these locate in a vee groove in the ota fitting ring/adapter. Many cheaper focusers have steel screws and a bit of grease. Better ones have nylon or delrin grub screws which have better feel.

You can adjust the feel by tweaking these grub screws or even changing the grease. If the lock screw isnt nylon tipped, this can put dimples in the vee groove and make rotating feel rough, the moral of the story is dont overtighten the lock screws.

Edited by philjay

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Nightspore
8 minutes ago, philjay said:

Yep, thats a threaded hole, so you can either put another thumb screw in there or swap the existing one to it.

Rotating focusers. Most focusers use 3 screws 120 deg apart on the body, one being the lock screw the others grub screws, these locate in a vee groove in the ota fitting ring/adapter. Many cheaper focusers have steel screws and a bit of grease. Better ones have nylon or delrin grub screws which have better feel.

You can adjust the feel by tweaking these grub screws or even changing the grease. If the lock screw isnt nylon tipped, this can put dimples in the vee groove and make rotating feel rough, the moral of the story is dont overtighten the lock screws.

OK thanks philjay. I'm going to see if I can find a second thumb screw that will fit. I'd feel safer with two thumb screws and a heavy 2" prism diagonal and a large eyepiece.

Edited by Nightspore

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Nightspore

A second thumb screw is proving difficult to find.

 

4XLmIH3.jpg

 

I did swap it over to the left though. Which makes it much easier for me as I'm partially paralysed in the right arm and hand.

 

mXJOhfw.jpg

 

Sorted!

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Bino-viewer

Glad its all ok.

Looking back through this thread with the rotation problems,

i'm surprised with you using the alt-az AZ5 you actually NEED to rotate the focuser at all ?

 

I know this feature is useful if one was using an equatorial mount with the resulting eyepiece 

positions after slewing, or when say, framing an object with a DSLR if you were imaging, but with an alt-az

the eyepieces are always in the optimum position.

 

When i had my last refractor, that had a rotatable focuser, but i didn't really use it a lot, other than like i said,

if i had a camera on the back, with was a fairly rare event.

 

I also think that to make a GOOD rotatable focuser, theres probably more engineering required than you may think.

 

 

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Nightspore

Thanks, OVL originally sent me the wrong size screws. They were for the 1.25" adapter, one of them fixed my Luminos Barlow though. The original Luminos adapter screw was faulty. OVL then sent me the correct size but didn't charge me. So, all's well that ends well lol.

 

gxih7WZ.jpg

 

You're forgetting that the eyepiece position on a refractor changes height as the telescope altitude moves from the horizontal to the zenith. If I set the height of the tripod so I can be comfortably seated and observe at the zenith it would be impossible to sit and observe without either rotating the diagonal or the focuser.

 

cBbP8bE.jpg

 

I often stand to observe for a while, especially if I'm sweeping star fields, but long periods of observing necessitate being seated IMO.

 

4ieEPvG.jpg

 

A lot of this has to do with my disability. Standing and sitting are fairly easy for me to accomplish, but everything in-between is difficult or painful. 

 

nR7YldQ.jpg

 

Rotating heavy prism diagonals and eyepieces isn't that manageable when you have limited range and dexterity in one arm. I'd hate to drop anything expensive lol. I'm glad my 102mm Altair Starwave has a rotating focuser.

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