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A Tale of Two Focusers

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#26 Redbetter

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Posted 07 December 2019 - 12:30 PM

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

No, he said the stock Orion focuser had 5-1/4" of travel, which is what I find confusing.  A draw tube long enough to provide that much travel would stick through an inch or so past/through the baffle when racked all the way in..   

 

The GSO's (two Lunt 2" dual speed that I have) have ~73mm of travel.  The Orion 1.25" is about 1" longer racked all the way in (less back focus), because of that threaded visual back piece on the draw tube.  This is in comparison to the 2" GSO without the 1.25" adapter inserted. 



#27 Shorty Barlow

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Posted 07 December 2019 - 01:35 PM

No, he said the stock Orion focuser had 5-1/4" of travel, which is what I find confusing.  A draw tube long enough to provide that much travel would stick through an inch or so past/through the baffle when racked all the way in..   

 

 

This, or something similar, is what I was told about the 2" GSO afermarket focuser. Which apparently cuts into the light cone in effect diminishing the size of the objective by a few millimetres. This is getting way too complicated lol. At the end of the day, the GSO's worked fine in my ST80's if you didn't rotate the focuser. With a 2" diagonal I don't recall needing an extension tube, but with a 1.25" diagonal I often had to use an extension tube.



#28 Redbetter

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Posted 07 December 2019 - 02:57 PM

This, or something similar, is what I was told about the 2" GSO afermarket focuser. Which apparently cuts into the light cone in effect diminishing the size of the objective by a few millimetres. This is getting way too complicated lol. At the end of the day, the GSO's worked fine in my ST80's if you didn't rotate the focuser. With a 2" diagonal I don't recall needing an extension tube, but with a 1.25" diagonal I often had to use an extension tube.

That bit about the 2" GSO focuser in the ST80 is almost certainly wrong for several reasons.  The most obvious is that a chief complaint about the ST80 is that the baffle itself restricts the fully illuminated field to either a few mm, or possibly even reduces the aperture in 1.25" with the stock focuser.  But if you move the baffle back to open things up the 1.25" draw tube is still narrower than the 2" drawtube.  So it becomes a matter of how far racked in the draw tube is to achieve focus.  And for 1.25" operation the draw tube is racked way out, so the front edge of the draw tube is less of an issue.    At f/5 in 2" mode the draw tube is limiting to the fully illuminated field even with the baffle moved all the way back, but that is for a much wider field.

 

However your focuser is not the same GSO focuser typically used in the 80 f/5's.  That 50mm drawtube range is the tip off. 



#29 Shorty Barlow

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Posted 07 December 2019 - 03:44 PM

That bit about the 2" GSO focuser in the ST80 is almost certainly wrong for several reasons.  The most obvious is that a chief complaint about the ST80 is that the baffle itself restricts the fully illuminated field to either a few mm, or possibly even reduces the aperture in 1.25" with the stock focuser.  But if you move the baffle back to open things up the 1.25" draw tube is still narrower than the 2" drawtube.  So it becomes a matter of how far racked in the draw tube is to achieve focus.  And for 1.25" operation the draw tube is racked way out, so the front edge of the draw tube is less of an issue.    At f/5 in 2" mode the draw tube is limiting to the fully illuminated field even with the baffle moved all the way back, but that is for a much wider field.

 

However your focuser is not the same GSO focuser typically used in the 80 f/5's.  That 50mm drawtube range is the tip off. 

I honestly don't know. The GSO focusers I used were the heavy duty ones I think. I have two ST80's, the first was a Sky-Watcher.

 

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I spent a lot of time trying to get a tripod/mount combination that worked with the ST80. The AZ3 had serious altitude drift. I eventually ended up with a Porta II/Hal-130.

 

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I also bought new eyepieces etc. The SW had a stuck dew shield and other problems. So it was a 'no brainer' to just replace the OTA. I got an Orion as I could buy it without a mount. 

 

gallery_249298_5348_81285.jpg

 

When I decided to upgrade the focuser I used the Orion first. I bought the heavier duty focuser. At the time it was the only type I could easily purchase. But it worked pretty well and I kept buying the same sort as I upgraded.


Edited by Shorty Barlow, 07 December 2019 - 03:53 PM.


#30 jcj380

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Posted 31 January 2020 - 09:33 AM

Do the Lunt Crayfords rotate?  I don't see anything like the silver ring on the GSOs or a setscrew in the Lunt pics.


Edited by jcj380, 31 January 2020 - 09:34 AM.


#31 ares53405

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Posted 31 January 2020 - 07:06 PM

Yes, the Lunt focusers rotate but they do not come with a rotation thumb screw...just a set screw.  You can remove it and replace it with a thumb screw.  The only GSO focuser that comes with a silver rotation collar is the larger one with the 112.5mm adapter.  The smaller ones are black.  The tube travel on the standard GSO focuser is 79mm (3.11").  The tube travel on the Linear Bearing Focuser is 50.8mm (2").  Hope this info helps.

 

Mark


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#32 Shorty Barlow

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Posted 06 February 2020 - 04:09 AM

I don't think the Lunt focusers were designed to be rotated as you observe, although they can be rotated. Plus they only have one set screw for the visual back as far as I know.



#33 Redbetter

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Posted 10 February 2020 - 09:40 PM

I don't think the Lunt focusers were designed to be rotated as you observe, although they can be rotated. 

They are the same as the GSO's in that regard.  They can be rotated during observation, but you will have to provide your own set screw to lock and unlock the rotation.  From what I can tell it is the same focuser from the same manufacturer with very minor differences.

 

I was just rotating mine in an LT80 to view Mercury on GEM mount.



#34 Shorty Barlow

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Posted 10 February 2020 - 10:04 PM

They are the same as the GSO's in that regard.  They can be rotated during observation, but you will have to provide your own set screw to lock and unlock the rotation.  From what I can tell it is the same focuser from the same manufacturer with very minor differences.

 

I was just rotating mine in an LT80 to view Mercury on GEM mount.

The GSO's were designed to be rotated while observing as far as I can tell, they're just rubbish at it. The Lunt has a lot of dissimilarities with the GSO, and although ostensibly it is very similar, there's no evidence they both originate from the same manufacturer. In fact, I'd doubt it.



#35 Redbetter

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Posted 11 February 2020 - 12:05 AM

The GSO's were designed to be rotated while observing as far as I can tell, they're just rubbish at it. The Lunt has a lot of dissimilarities with the GSO, and although ostensibly it is very similar, there's no evidence they both originate from the same manufacturer. In fact, I'd doubt it.

You have misidentified it. Have you looked at actual branded GSO's or the Lunts that have been discussed?  They are identical except for the printing, lack of screw inserted for rotation (4th hole is there in the correct position) and the lack of a second set screw/hole for the compression ring.  The Lunt 2" (link) has a 3" long draw tube, same dimensions as the GSO 2"  listed on Agena's site.   Same rotation grub screws, same extra spot for the rotation set screw (but without the screw), same finder mount locations.  Same knobs/same screw pattern on the bottom.

 

The one that seemed doubtful to me as a GSO is your TS with its short draw tube.  It looks like something between the Kunming(?) focuser on my 110ED and a GSO.   It doesn't look like the branded GSO on our Z10 Dob or the two Lunt/GSO's (that look very much like the Z10's focuser except for the longer draw tube and refractor vs. Dob flange piece.)  In fact looking at the TS's I also notice they have a separate rail added that is not on the GSO or GSO/Lunt's.  And the base plate of the focuser assembly looks much different. 

 

But that rail explains why you are confused about this and why I began to wonder if the TS was a GSO.  Doing some searching that short TS is the short "GSO 2" Linear Bearing Crayford Focuser for Refractors" on Agena's site (which runs $100 more than the Lunt GSO.)  The 110ED's focuser with that sort of rail has had some issues, particularly with uneven grip/backlash/rollback on the rail, but I presume it was a problem with the execution because I read of some others with the same problem.  

 

EDIT for broken link.


Edited by Redbetter, 11 February 2020 - 03:57 PM.

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#36 Shorty Barlow

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Posted 11 February 2020 - 05:02 AM

You have misidentified it. Have you looked at actual branded GSO's or the Lunts that have been discussed?  They are identical except for the printing, lack of screw inserted for rotation (4th hole is there in the correct position) and the lack of a second set screw/hole for the compression ring.  The Lunt 2" (link) has a 3" long draw tube, same dimensions as the GSO 2"  listed on Agena's site.   Same rotation grub screws, same extra spot for the rotation set screw (but without the screw), same finder mount locations.  Same knobs/same screw pattern on the bottom.

 

The one that seemed doubtful to me as a GSO is your TS with its short draw tube.  It looks like something between the Kunming(?) focuser on my 110ED and a GSO.   It doesn't look like the branded GSO on our Z10 Dob or the two Lunt/GSO's (that look very much like the Z10's focuser except for the longer draw tube and refractor vs. Dob flange piece.)  In fact looking at the TS's I also notice they have a separate rail added that is not on the GSO or GSO/Lunt's.  And the base plate of the focuser assembly looks much different. 

 

But that rail explains why you are confused about this and why I began to wonder if the TS was a GSO.  Doing some searching that short TS is the short "GSO 2" Linear Bearing Crayford Focuser for Refractors" on Agena's site (which runs $100 more than the Lunt GSO.)  The 110ED's focuser with that sort of rail has had some issues, particularly with uneven grip/backlash/rollback on the rail, but I presume it was a problem with the execution because I read of some others with the same problem.  

I haven't misidentified anything. They look very similar but there are differences. TS sell different aftermarket refractor focuser types, all three of mine are GSO as I was told this by someone at TS Optics when I enquired. Mine are just the heavier duty variant. 

 

Edited as requested.


Edited by Shorty Barlow, 11 February 2020 - 08:34 AM.


#37 beanerds

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Posted 11 February 2020 - 06:47 AM

Yes, the Lunt focusers rotate but they do not come with a rotation thumb screw...just a set screw.  You can remove it and replace it with a thumb screw.  The only GSO focuser that comes with a silver rotation collar is the larger one with the 112.5mm adapter.  The smaller ones are black.  The tube travel on the standard GSO focuser is 79mm (3.11").  The tube travel on the Linear Bearing Focuser is 50.8mm (2").  Hope this info helps.

 

Mark

The Linear bearing focuser also has only 2 inches ( 50.8 mm ) of travel but its plenty for my ED100 with careful measuring for the alloy adapter I machined up  / I had mine apart for this .

 

The ' Linear bearing ' they are talking about is 4 small bearings that run along the length of the track on the underside giving great side to side stability ,  these still have the 4 ' Crayford ' bearings in the body like all Crayfords have  for focus .

 

It's a nice focuser with 360* rotation as well .  Just remove the lock knob cut a small piese of teflon about 3mm deep and 4mm ish in diameter and drop in down the hole , refit the knob , tighten a little , give the focuser a few rotations , tighten until happy and BINGO ! perfect 360* smooth rotation .

 

Beanerds.

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Edited by beanerds, 11 February 2020 - 07:02 AM.


#38 Jon Isaacs

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Posted 11 February 2020 - 07:24 AM

For what it's worth:

 

The Lunt Crayford Red is referring to is identical to the standard GSO Crayford. I know these Focusers intimately, i have three of them, I've had others. Some have 2 set screws, some have 1.

 

Short Barlows Focusers are not the standard GSO Crayford, he identified them as a linear bearing GSO Crayford and the focuser locking screw on top identifies them as such. I've had one of these. I'm not fond of them, the pinion block assembly is plastic. The other issue is the linear bearing is not sealed. In the dusty environments I observe in, that's a problem because linear bearings are sensitive to dust and grime. 

 

As far as caffeine goes, I avoid the stuff like the plague. 

 

Jon


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#39 Redbetter

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Posted 11 February 2020 - 03:49 PM

I haven't misidentified anything. They look very similar but there are differences. TS sell different aftermarket refractor focuser types, all three of mine are GSO as I was told this by someone at TS Optics when I enquired. Mine are just the heavier duty variant. 

 

Edited as requested.

 

You are definitely mistaken about the Lunt/GSO, which you have zero experience with.  



#40 Shorty Barlow

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Posted 07 April 2020 - 07:22 AM

A tale of three focusers or "MoonLite Becomes Her".

 

med_gallery_249298_10069_31923.jpg


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#41 m9x18

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Posted 07 April 2020 - 09:12 AM

A tale of three focusers or "MoonLite Becomes Her".

 

med_gallery_249298_10069_31923.jpg

Wow! Beautiful and practical all at the same time. That green MoonLite really goes with that scope!


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#42 Shorty Barlow

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Posted 07 April 2020 - 09:36 AM

Wow! Beautiful and practical all at the same time. That green MoonLite really goes with that scope!

Thanks. Admittedly I nearly went for the blue, but green does kind of blend well lol. It is beautifully made, rotates virtually perfectly and seems incredibly smooth and precise. Even better, my 14mm Morpheus reaches focus now with the APM diagonal!

 

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#43 Shorty Barlow

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Posted 07 April 2020 - 10:25 AM

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It's been a bit of a journey.

 

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#44 m9x18

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Posted 07 April 2020 - 10:45 AM

Yep. My vote is for the MoonLite.


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#45 Shorty Barlow

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Posted 07 April 2020 - 10:51 AM

Yep. My vote is for the MoonLite.

Definitely.


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#46 Shorty Barlow

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Posted 08 April 2020 - 07:16 AM

med_gallery_249298_10069_142421.jpg

 

Dorsal view (above) 

 

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The view underneath showing the shaft lock system knob next to the focuser control and the lifting capacity adjustment knob in the centre of the housing.


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#47 m9x18

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Posted 08 April 2020 - 01:36 PM

Sweet!


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#48 Shorty Barlow

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Posted 09 April 2020 - 10:03 AM

I got first light with the new focuser. I was set-up by 20:00 BST and the plan was to catch a setting Venus and as it got darker to try some rich field before the Moon was too high. I estimated that if I was lucky I may have until 21:30 until the Moon was a problem. As it was warm, sunny, and there had been a pristine and cloudless sky all day, I reckoned I was in with a chance. Of course, at 20:30 cloudy sky porridge filled the entire firmament effectively ending the session.

 

med_gallery_249298_10069_106346.jpg

 

The first thing I’d noticed about the MoonLite was its weight compared to the Sky-Watcher (Long Perng) focuser unit. The SW with a Baader 1.25” adapter is 565g. The MoonLite with its stock adapter is 890g. Some 325g difference. I’d been using the SW focuser for nearly eleven months and had got used to the OTA being lighter than when it had the TS Optics (GSO) unit fitted. The TS Optics/GSO focuser with its original 1.25” adapter is 860g compared to the MoonLite at 890g. I don’t need the Baader (or MoonLite) adapter normally so by losing the adapter the MoonLite is ‘only’ 225g heavier than the SW focuser and roughly compares with the overall weight of the GSO.

 

med_gallery_249298_10069_151241.jpg

 

My ST102 is fundamentally a rich field scope and it is the biggest refractor I can easily transport and set-up on the SW AZ5 mount/tripod. As a consequence I rarely use magnifications above around 60x and I’m usually observing between 18.5x and 42x. I only take two eyepieces out with it (27mm Panoptic, BHZ). I also take out a Celestron Luminos 2.5x Barlow in the grab and go bag for occasional higher magnifications. In use the Barlow usually has a Baader Fringe Killer/Neodymium stack threaded into it.

 

med_gallery_249298_10069_193566.jpg

 

When I initially set up the MoonLite I noticed that the focusing controls and the rotation were very smooth. An odd thing was that I noticed that the left-hand finder shoe screw would push the reflex sight foot slightly forward as it rotated and tightened. To keep the finder as accurate as possible I usually push the foot into the shoe while feeling for the edge of the shoe with my finger. When it is flush with the edge I know it is in the right place. This is a particularly useful operation when setting up in the dark. It does this every time I place the reflex sight into the shoe though so once the finder has been aligned it doesn’t matter as it always slides back to the same place.

As I was observing Venus at between around 100x to 156x the extra weight of the MoonLite was quite noticeable. The vibration return at these magnifications was slower than with the lighter SW unit. I discovered that the smoothness and precision of the focusing controls offset this slightly though. Another interesting factor was the MoonLite’s shaft lock system situated directly under the left-hand focusing knob. This locks with absolutely no image shift that I could detect.

 

med_gallery_249298_10069_132373.jpg

 

Just before the sky porridge came I had a look at Sirius, Procyon and Cappella at 18.5x with the Panoptic. It was still technically twilight but these particular stars are very bright. Any vibration was not an issue at this magnification. The only drawback appears to be getting used to the extra weight again. All in all I’m very impressed with the MoonLite and it is a joy to use. It oozes quality and is beautiful to look at. I’ll have to eventually stop taking jpegs of it lol.


Edited by Shorty Barlow, 09 April 2020 - 10:19 AM.

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#49 Jond105

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Posted 09 April 2020 - 10:23 AM

I miss my moonlite focusers. They really are such a great focuser. Nice set up Shorty


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#50 Shorty Barlow

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Posted 09 April 2020 - 10:28 AM

I miss my moonlite focusers. They really are such a great focuser. Nice set up Shorty

Thanks. I decided that as the ST102 gets out so much it should have a really good focuser lol.


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