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A Tale of Two Focusers

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#1 Shorty Barlow

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Posted 01 June 2019 - 11:55 AM

 
gallery_249298_10069_865627.png

 

In January 2018 I bought a Sky-Watcher ST102 StarTravel as an inexpensive rich field grab'n'go scope. Although I originally intended to use it on a Vixen Porta II/SXG tripod combination I discovered it would quite easily balance well on my Sky-Watcher AZ5. This made it even more of a grab'n'go scope for me. I never used it as stock and replaced its original focuser with a dual speed heavy duty TS Optics (GSO) rotating Crayford-rail focusing unit virtually the same as on my modified ST80's. This was fine and worked really well after I added twin finder shoes, a Baader adapter, and sorted out all of the back or in-focusing problems and suitable accessories etc.

 

gallery_249298_10069_78704.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 italics).

 

gallery_249298_10069_64371.jpg

 

Trouble is, apparently I'm not 'most people' and now find the feature indispensable. 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 believe that it is related to the way the actual mechanism works. The rotating bit (technical jargon lol) 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 should have read the small print more closely.

 

gallery_249298_10069_105624.jpg

 

Fortunately Sky-Watcher are now making their replacement focusers with finder shoe holes, which is a bit of a deal breaker for me. So I removed the TS Optics focuser and replaced it with the dual speed Sky-Watcher Crayford equivalent.

 

gallery_249298_10069_109020.jpg

 

There is a definite improvement in rotation. The 'rotating bit' doesn't sag when the rotational screw is loosened and the mechanism seems as smooth as the focuser on my Altair Starwave. There is only one screw to hold the diagonal however, unlike the pair of screws on the GSO focuser. The one screw seems capable enough in use though. The focal plane has now changed as the new focuser is physically longer (132mm + 80mm when draw tube fully extended). This has caused in-focusing problems with some eyepieces but in the main everything's fine. In fact I even thought that the focusing itself was smoother and more precise. And of course it was way cheaper than a MoonLite! lol


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#2 Redbetter

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Posted 01 June 2019 - 04:48 PM

A tale of three focusers perhaps?  It looks like 3 different ones to me:  Stock Synta base model (single speed?), then a TS badged GSO dual speed, then a Skywatcher Crayford replacement. 

 

About the lack of a 2nd screw for holding the diagonal:  I had the same issue with the 2" GSO dual speeds from Lunt.  It was an easy fix though since both are compression ring. 

  • I selected a point for a second screw, and rotated the ring's gap to that position.  (I chose straight up, 90 degrees from the other, this would lock things in both axes.)
  • I then drilled a hole through from the outside (using a bit for it from a metric tap and dye set.)
  • I tapped the hole for the same standard threads as used for the set screws. 
  • Finally, I rotated the gap away from the set screw holes, and inserted a set screw into the new hole.

The focusers now hold the diagonals firmly in both axes. 


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#3 Shorty Barlow

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Posted 02 June 2019 - 05:56 AM

A tale of three focusers perhaps?  It looks like 3 different ones to me:  Stock Synta base model (single speed?), then a TS badged GSO dual speed, then a Skywatcher Crayford replacement. 

 

About the lack of a 2nd screw for holding the diagonal:  I had the same issue with the 2" GSO dual speeds from Lunt.  It was an easy fix though since both are compression ring. 

  • I selected a point for a second screw, and rotated the ring's gap to that position.  (I chose straight up, 90 degrees from the other, this would lock things in both axes.)
  • I then drilled a hole through from the outside (using a bit for it from a metric tap and dye set.)
  • I tapped the hole for the same standard threads as used for the set screws. 
  • Finally, I rotated the gap away from the set screw holes, and inserted a set screw into the new hole.

The focusers now hold the diagonals firmly in both axes. 

Well, a tale of two rotating focusers. I couldn't fit it all in the title lol. I never really used the stock Synta focuser, it isn't that bad but, as you said, it's only single speed.

 

gallery_249298_10069_103629.jpg

 

The GSO was significantly shorter and I often needed an extension tube to achieve focus. I finally thought I'd sussed it all out when I discovered my 2" APM Amici diagonal was a perfect match and every eyepiece I own focused with it.

 

gallery_249298_10069_525804.jpg

 

I like your DIY approach to adding a second thumb screw. I may have spoken too soon about a lack of a second thumb screw on the Sky-Watcher. On closer inspection I noticed there was a screw with a slotted head which appears to be a place holder for a second gnarled thumb screw. It's also in exactly the same position (looks like about 120°) as the second screw on the original stock focuser. Unfortunately I have no thumb screws that fit it at the moment. 


Edited by Shorty Barlow, 02 June 2019 - 06:00 AM.


#4 Shorty Barlow

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Posted 04 June 2019 - 05:09 AM

I've been making enquiries about obtaining a second screw from a Sky-Watcher importer into my country. 

 

 

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The thumb screw and placeholder grub screw are interchangeable. 



#5 LDW47  Happy Birthday!

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Posted 05 June 2019 - 08:47 AM

So did you take out the set screw in the other hole and try the screw that you do have to see if it is the same threads / diameter ? I am sure that a good hardware store could accommodate you or get you the size and buy after market on line ! Maybe you have and I missed it ?



#6 Shorty Barlow

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Posted 06 June 2019 - 04:21 AM

So did you take out the set screw in the other hole and try the screw that you do have to see if it is the same threads / diameter ? I am sure that a good hardware store could accommodate you or get you the size and buy after market on line ! Maybe you have and I missed it ?

Yes, see above picture. As far as I can tell the market for gnarled thumb screws isn't large. A bloke from OVL (importer and retailer) said he'd contact Synta for me about obtaining a second thumb screw. 


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#7 LDW47  Happy Birthday!

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Posted 06 June 2019 - 04:08 PM

Yes, see above picture. As far as I can tell the market for gnarled thumb screws isn't large. A bloke from OVL (importer and retailer) said he'd contact Synta for me about obtaining a second thumb screw. 

I don’t know if Bob’s Knobs is still around in the US but it seems he may have had some !



#8 LDW47  Happy Birthday!

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Posted 06 June 2019 - 06:12 PM

Yes, see above picture. As far as I can tell the market for gnarled thumb screws isn't large. A bloke from OVL (importer and retailer) said he'd contact Synta for me about obtaining a second thumb screw. 

Also Agena Astro in the US has a big selection of thumb screws, all you need is the thread size and maybe the diameter ! Google them on line !



#9 Shorty Barlow

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Posted 06 June 2019 - 10:26 PM

Importing stuff from the US isn't always that easy. OVL have ordered some for me.


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#10 Simon B

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Posted 07 June 2019 - 01:29 AM

Nice, I love rotating focusers I use the feature all the time : )  perhaps I'm lucky - the rotating feature on my GSO crayford has never been a source of any problems, with either sag or focus movement

 

 

Regarding the 'grinding' in the focuser knob of the GSO crayford - I had the same issue with mine. After following these instructions, the focuser became silky smooth again *(step 7 in particular!)

 

https://agenaastro.c...rd-focuser.html


Edited by Simon B, 07 June 2019 - 01:30 AM.

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#11 Shorty Barlow

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Posted 07 June 2019 - 08:02 AM

Nice, I love rotating focusers I use the feature all the time : )  perhaps I'm lucky - the rotating feature on my GSO crayford has never been a source of any problems, with either sag or focus movement

 

 

Regarding the 'grinding' in the focuser knob of the GSO crayford - I had the same issue with mine. After following these instructions, the focuser became silky smooth again *(step 7 in particular!)

 

https://agenaastro.c...rd-focuser.html

Thanks, that's interesting. I never had any trouble with the GSO focusers on my ST80's, although I rarely rotated the focuser. I've noticed that they all drop or sag when untightened though.

 

gallery_249298_10284_110502.jpg

 

Orion ST80 with TS Optics/GSO focuser with rotation tightened.

 

gallery_249298_10284_75610.jpg

 

Now with rotation screw untightened. It seems to be a feature of the design to me. 



#12 Shorty Barlow

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Posted 18 July 2019 - 06:36 AM

Finally, after a slight mix-up in screw sizes, success!

 

gallery_249298_10069_35908.jpg


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#13 SloMoe

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Posted 28 November 2019 - 07:13 PM

The rotation set up on mine is three socket head set screws and a position lock thumb screw.

You'll see them in line with the thumb lock screw around the focuser body.

 

The three set screws are  angle tipped, come to a point, and ride in a "V" groove, the thumb screw is also "V".

the tips are full metal, no plastic so when you rotate the focus housing those set screws are the "bearing", the groove and the set screws tip aren't a perfect match so the edge or tip will drag a bit.

 

I filed the edges of the three set screws so that the contact surface was smooth not the machined sharp edge of the end of the set screws threads and the start of the tip.

 

To round them I first tried to do it using a drill, I cut my Allen wrench off so it was just a straight shank, then set the socket end of the screw on it, started the drill and rested my fish hook file on the edge of the set screw,,,,,,, never found that set screw so I just filled them by hand and made the missing third one from another set screw. 

 

There is a plastic washer between the rotation section and the OTA tube end of the unit, I think,,,,,,

maybe it was on my Zenithstar, did the same thing to it and on that one I didn't have to make a third set screw,,,,,

 

I guess if you wanted to smooth up the rotation of the housing you could add a dab of grease to the grove, remove the thumb  screw completely and back the set screws nearly all the way out, now separate the housing from the OTA adapter ring. 



#14 Schurke

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Posted 29 November 2019 - 09:47 AM

Orion ST80 with TS Optics/GSO focuser


I can't seem to find the right TS focuser for my skywatcher ST80. Can someone link it for me?

#15 SloMoe

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Posted 29 November 2019 - 11:09 AM

Importing stuff from the US isn't always that easy. OVL have ordered some for me.

To get a collection of thumb screws I've replaced many unused thumb screws on my scopes with socket head set screws, 

Like in 1.25" to 2" adapters that just stay on the eyepiece, the tension adjustment thumb screws on the draw tubes, most of the time once those are set I never fiddle with them, even then if I do need a slight adjustment to the tension an Allen wrench tweek, 

 

And with some of the six point finder ring mounts, I'll either find an "O" ring for the front ring or socket head set screws to replace the three in the front ring, 

 

To me a bunch of unused thumb screws on a scope makes it appear to be sort of Frankenstein'ish, and it's just a few less things to get hung up or snag sleeves in the dark, ya know?

 

In the pic you can see where I used socket head set screws to replaced unused thumb screws, on the adapter just under the illuminator for my redicel eyepiece I use in my Dob, on the upper finder, that's a 45° finder I found in the classifieds for terrestrial viewing, the front ring you'll see the missing six point thumb screws, on the GSO I only use 1.25" diagonals so the 1.25" adapter has a set screw, plus the ring that holds the 2" extension tube has one and on the bottom of the focuser I replaced the draw tube tension thumb screw,  on the Orion 70mm Multi-use finder I also used set screws for the front ring

 

If I'm lucky I find the set screws in black, but some I had to use stainless set screws for the size, length, and thread pitch.

 

Just an idea of how to make your own collection of thumb screws,,,,, left overs,,, speaking of left overs bet you're eating turkey for the next few days,!cool.gif

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Edited by SloMoe, 29 November 2019 - 11:10 AM.

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#16 SloMoe

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Posted 29 November 2019 - 11:17 AM

Yeah, the 45's a cobble project, the shoe cam from Scopestuff and I drilled the bracket that came with the finder to secure it to, I wanted a low profile height for it, you can see one of the screws through what used to be a hole for a fastener that squeezed a clamp to a different style shoe.

 

All of my finders have Vixen/Synta shoes, and they're reversed so the foot of the finder slides in from the front rather than the back, that way if I fail to get the thumb screw tight and swing the scope skywards the finder won't drop back out.  waytogo.gif



#17 SloMoe

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Posted 29 November 2019 - 11:20 AM

Here's a link to a focuser selection, make sure you accurately measure your OTA  inside diameter 

 

https://agenaastro.c...ccessories.html



#18 SloMoe

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Posted 29 November 2019 - 11:48 AM

And here's the first project that started the thumb screw collection and still remains the only SAE thread thumb screw I own,

 

It's a Hotec Cross hair 1.25" laser, I had to true up the laser even in the Parallizer to remain in collimation for a constant registration every time no matter how it's set in, and using three different 2" lasers to compare against it's collimation

Farpoint, Astrosyatems and later Howie's own.

 

Not only did I use shims in the adapter I found the alignment screws Hotec had hidden on their laser.

 

And yes, there's a socket headed set screw in there, nobody can fiddle with it,   cool.gif

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Edited by SloMoe, 29 November 2019 - 12:50 PM.


#19 Shorty Barlow

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Posted 02 December 2019 - 08:48 PM

I can't seem to find the right TS focuser for my skywatcher ST80. Can someone link it for me?

TS Optics 2" Monorail Focuser for Refractor telescopes

 

https://www.teleskop...6mm-flange.html

 

This is the model on my ST80's.

 

med_gallery_249298_10284_22312.jpg



#20 SteveG

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Posted 03 December 2019 - 12:05 AM

TS Optics 2" Monorail Focuser for Refractor telescopes

 

https://www.teleskop...6mm-flange.html

 

This is the model on my ST80's.

 

med_gallery_249298_10284_22312.jpg

 

The spec's state 50 mm of focuser travel (2"). Is that enough? My Orion stock focuser has 5-1/4" of travel. I could probably live with less, but not 2" of travel.



#21 Shorty Barlow

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Posted 03 December 2019 - 07:30 AM

The spec's state 50 mm of focuser travel (2"). Is that enough? My Orion stock focuser has 5-1/4" of travel. I could probably live with less, but not 2" of travel.

It is 50mm.

 

med_gallery_249298_10284_179566.jpg

 

My guess would be that it's impractical to make it longer for some reason. Perhaps because of the rotating mechanism. There are theories that the 2" focusers cut into the light cone effectively reducing the aperture to 72mm. Interestingly I replaced my ST80's with a 72mm Evostar. 

 

med_gallery_249298_10284_88809.jpg

 

The 50mm travel explains this phalanx of extension tubes I used with the modified ST80's. Although I don't recall any in-focus problems.

 

med_gallery_249298_10284_182834.jpg

 

It's the same travel on the larger focuser intended for 4"/10 cm OTA's. Bear in mind the 2" focuser was also intended for a 2" diagonal, which can increase the overall length. I only used the extension tubes when using a 1.25 diagonal IIRC.



#22 Schurke

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Posted 03 December 2019 - 09:46 AM

TS Optics 2" Monorail Focuser for Refractor telescopes

https://www.teleskop...6mm-flange.html


Thank you.

#23 Shorty Barlow

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Posted 03 December 2019 - 10:56 AM

Thank you.

You're welcome.



#24 Redbetter

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Posted 07 December 2019 - 05:25 AM

The spec's state 50 mm of focuser travel (2"). Is that enough? My Orion stock focuser has 5-1/4" of travel. I could probably live with less, but not 2" of travel.

Typo?  My ST80's focuser (and the Meade AS 80 f/5) have ~61mm of travel...roughly 2 3/8" or a little more.  Are you talking about a different focuser than the stock one?



#25 Shorty Barlow

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Posted 07 December 2019 - 07:20 AM

Typo?  My ST80's focuser (and the Meade AS 80 f/5) have ~61mm of travel...roughly 2 3/8" or a little more.  Are you talking about a different focuser than the stock one?

I think Steve was referring to the aftermarket GSO focuser, which has 50mm of travel. 




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