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Goto Optical 3" Single (Mono) Axis 76mm 1200mm fl. Redux

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#1 Stew44

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Posted 10 January 2021 - 09:55 PM

In early 2019 I acquired what I thought was an orphaned (no mount) Goto 3" telescope in its case with accys.  I discussed its condition and my impressions here:

 

https://www.cloudyni...is#entry9615568

 

It turns out that I now believe it came over from Japan that way as certain features that are necessary for the mount to function are missing from this OTA.  

 

I have only seen one other of these telescopes on CN (owned by strdst for the last twelve years) with mount.  The only other I've seen has been in pictures from the Japanese Telescope Museum.  I believe the mount in particular is rarer than the similar mount accompanying the 60mm Eros telescopes from the same period (roughly 1951-1954).  And a lighter weight yet mount was offered with a Comet OTA as the Castor.  All three of these dual pendulum counterweight mounts (Castor, Eros and this 3" Single Axis), matched with properly scaled OTAs, according to information on Galakuma's site, were designed by Goto-san's protégé Mr. Shusuke Kojima. 

 

I encouraged strdst to post on this mount because it was built at a time where materials in Japan and machining capability were scarce.  That post is here:

 

https://www.cloudyni...is#entry9376701

 

I really didn't expect to ever find a mount for my OTA, but recently strdst quite generously offered me the opportunity to acquire the mount.  It arrived a couple days ago and I finally got things cobbled together.  This is the scope set up for for southern hemisphere to zenith.

 

P1010355.JPG

 

P1010356.JPG

 

As we will see this is fully functional as a single axis mount.  But as strdst noted, operating the mount is not intuitive.  It took a little time to sort out the differences between it and the similar Eros mounts I have.  Here it is setup for polar alignment using the OTA.

 

P1010357.JPG


Edited by Stew44, 11 January 2021 - 09:12 PM.

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#2 Stew44

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Posted 10 January 2021 - 09:59 PM

Here is a closeup of the mount configuration:

 

P1010359.JPG

 

Here to the west

 

P1010361.JPG

 

And here to the east

 

P1010362.JPG

 

It takes a bit to reconfigure from northern to southern hemisphere, and especially the pendulum weights need to be carefully kept out of the way during movement.

 

More to come as there are some wonderful features incorporated into this mount that are easily seen in follow-on Goto Optical products, and many Astro Optics and its derivative products as well.


Edited by Stew44, 10 January 2021 - 10:07 PM.

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#3 Bomber Bob

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Posted 10 January 2021 - 10:06 PM

Cool concept!  The only similar mount I've seen in R/L:  About 30 years ago, the BX (Base Exchange) started selling Galileo brand scopes, and at least one -- an 80mm Newt, IIRC -- used a pair of pendulum weights.

 

(When I first joined the USAF, the BX sold some top-tier Japanese scopes -- Nikon, Pentax -- but by the 1990s, ROC-made brands like the Galileo replaced them.)


Edited by Bomber Bob, 10 January 2021 - 10:14 PM.

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#4 PawPaw

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Posted 11 January 2021 - 09:58 AM

Stew I know how difficult it can be to make complete an orphaned OTA or mount and keep it original.  Absolutely  a fascinating design.

 

 

Can you explain the process of changing it from an equatorial mount to an Alt-azimuth?

 

Don


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#5 Stew44

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Posted 11 January 2021 - 10:19 AM

That's really pretty straight forward.  Just adjust the RA axis to vertical as in this picture and Dec mechanism to level the OTA.  The biggest challenge is figuring out which levered nut to loosen to adjust which part of the assembly.  Haven't figured out if I can separate the RA drive gear from the Dec mechanism to better position the cable extension (the school mounts allow this as BB has pointed out in previous posts).  But there are no setting circles so more convenience than need.

 

SA3 Alt Az.jpg


Edited by Stew44, 11 January 2021 - 10:59 AM.

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#6 Defenderslideguitar

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Posted 11 January 2021 - 10:38 AM

Sweet.  We just love it when a rarer  classic comes together. Cool design for sure



#7 Stew44

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Posted 11 January 2021 - 02:05 PM

The Single Axis 3" was apparently marketed through 1959.  Maybe they simply had mount inventory and because it wasn't a school telescope it didn't need to fit that formula for acceptance.  For whatever the reason it was updated after that time to 80mm f/15 and the mount(s) developed for the 4" were transitioned to the 3".  Here is my Mod 203 from early 60's.  Goto liked the leg set and called this the Field Tripod.  Compare with the lower picture.

 

Goto Mod 203.jpg

 

SA3.JPG

 

 

Attached Thumbnails

  • SA3a.JPG

Edited by Stew44, 11 January 2021 - 05:58 PM.

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#8 RichA

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Posted 11 January 2021 - 03:03 PM

That's really pretty straight forward.  Just adjust the RA axis to vertical as in this picture and Dec mechanism to level the OTA.  The biggest challenge is figuring out which levered nut to loosen to adjust which part of the assembly.  Haven't figured out if I can separate the RA drive gear from the Dec mechanism to better position the cable extension (the school mounts allow this as BB has pointed out in previous posts).  But there are no setting circles so more convenience than need.

 

attachicon.gifSA3 Alt Az.jpg

What a unique counter-weight system.



#9 clamchip

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Posted 11 January 2021 - 03:52 PM

Edmund Scientific was selling Goto in the early days.

This Eros? mono axis Edmund ad is from late 1952:

Robert

 

post-50896-0-81582000-1514253734_thumb.jpg


Edited by clamchip, 11 January 2021 - 03:53 PM.

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#10 dave brock

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Posted 11 January 2021 - 05:34 PM

Why is it referred to as a single axis mount?

#11 Stew44

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Posted 11 January 2021 - 05:51 PM

Why is it referred to as a single axis mount?

Typical mount today and on the 60's 3" above has two axes - RA and Dec.  So twice machining required for mount.  This one only has an RA axis.  Dec is a limited screw tilt mechanism riding on  the CW axis.  Has limited range of movement.



#12 dave brock

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Posted 11 January 2021 - 06:15 PM

So being pedantic (which I'm often accused of) it has two axes but limited slow motion in dec?

#13 Kasmos

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Posted 11 January 2021 - 08:18 PM

Stew, Your win but I can't understand why Keith would separate his OTA from the mount. I'm I missing something?



#14 Stew44

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Posted 11 January 2021 - 09:03 PM

So being pedantic (which I'm often accused of) it has two axes but limited slow motion in dec?

Yes in a nut shell.  The pivot pin and tilting mechanism doesn't require all the machining effort full Dec axis assembly would require.  I guess Goto didn't feel the pivot pin was a true Dec axis in the same vane as the Dec axis assembly in a typical dual axis GEM.



#15 strdst

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Posted 11 January 2021 - 09:49 PM

Stew, Your win but I can't understand why Keith would separate his OTA from the mount. I'm I missing something?

The devil made me do it.

 

Seriously, (and serious doesn't come easy for me), to provide (sell) an unobtainable item to complete a telescope in Stew's, (a true Goto scholar) collection feels terrific! My win as well! One complete telescope and one incomplete telescope becomes one incomplete telescope and one complete telescope...zero sum gain?


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#16 Dave Trott

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Posted 11 January 2021 - 11:02 PM

What a wonderful scope and fascinating mount! Congratulations, Stew!

 

- Dave




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