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''Goto'' Comet No3 f15/f20 60mm.

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#1 fsphotography

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Posted 14 August 2017 - 08:40 AM

Hi, i'm hoping someone on here can shed a bit of light on this rather odd ''GOTO'' scope that's fallen into my hands.

Promised Stew 44 some pic's some time ago and now finally got round to it. The file sizes were too big so could only fit three pic's, i will try to post the rest if there is any interest in this thread.

As describe in the title its a''Goto'' Comet No3  f15/f20 60mm. It came with the case, star diagonal, herschel wedge, sun and moon filters, finder scope(missing cross hairs) and several e.p.'s, including a rather strange erecting e.p.about 14 '' long. And a wooden oak tripod with a simple alt az swivel mount. The export standard label in the case in the case say's SEP 18 1954. There is also another label that states the model of the scope and contents of the case as provided.

Now for the odd bit. The scope is of an f15 tube and non-collimateble lens configuration, air spaced doublet. Unusually however it comes with with a interchangeable tube extension and f20 collimatable lens. Simply unscrew the f15 cell and screw on in it's place the f 20 tube exertion and cell.

How easy is that? And it actually works. Star tests superbly with either lens and the quality of the view is awesome. I prefer the f15 view, probably because its brighter. But both lenses are critically sharp with no c.a. whatsoever. As I've already said,'Awesome.

Thanks for reading,i hope some one out there knows more about this odd combination than i do.

Frank.

 

Attached Thumbnails

  • GOTO 4_edited-1.jpg
  • GOTO 7_edited-1.jpg
  • GOTO 3_edited-1.jpg

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#2 Stew44

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Posted 14 August 2017 - 08:57 AM

Thank you for posting.  Steve M. M. had the only 103 that I've found on CN so hopefully he can chime in.  This is truly unique and wonderful.  You get the benefit of the Kou 'school' Cooke doublet in the f/20 planetary killer lens, and the Best Optic Fraunhaufer in the f/15.  Part of me still thinks this is a salesman kind of package where they could show both lens types in a single portable package.  If that's the case then the lenses are probably a cut above so that the very best of each example is put out there for show.  Please add more pictures, especially of the lens rings and lens for each, and the documentation that accompanied the scope, and of course the mount, and well, also the accessories.  grin.gif

 

Certainly we can talk about components and what they do, but I've seen no reference to this kind of package.

 

I am well beyond envious, and think you are very fortunate indeed that this has fallen into your hands!

 

Cheers


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#3 Stew44

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Posted 14 August 2017 - 09:50 AM

One question - The Comet is a 40mm scope.  Are both of these lenses 40mm?  Interesting thing there is that there isn't a 40mm Fraunhaufer IIRC, until this one.



#4 Chuck Hards

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Posted 14 August 2017 - 09:55 AM

Judging from the finder size, those must be 60mm objectives, or the cells are massively over-sized.


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#5 Stew44

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Posted 14 August 2017 - 12:15 PM

I think given the change in tube diameter that the basic scope likely is 40mm, unless the baffling in the Comet tube and tube length would work with the focal length requirement of the 60mm f/15 lens.  The dew shields look the same size, so maybe a step up ring from the Comet tube to the 60mm f/15 cell, and then the f/20 60mm tube and cell with better baffling for the longer length.  The 40mm at 800mm is f/20 so it would only take a modest extension of the draw tube to adapt to the 900mm focal length.


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#6 Stew44

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Posted 15 August 2017 - 05:34 AM

The Comet was actually only 750mm focal length giving f/18.75.  That would add another 2" to an extended draw tube, so really do wonder if perhaps this is simply a Uranus/Eros OTA with non-collimatible cell on the Fraunhaufer doublet, with an extension to add the f/20 Cooke doublet.  He did describe this as a 60mm.

 

If true, then not really a Comet at all, but likely a nice collection of the then offered 60mm lens products in a case and perhaps labeled Comet for import purposes.

 

Mount is not shown and you can't determine if it is a sliding rod type of mount or two studs into an alt-az plate, or maybe just a clean tube (which wouldn't lend itself to demonstration of the optics).  Really would be nice to see more pictures please.

 

This is an actual Comet OTA owned by a CN'r with the studs on the bottom of OTA for alt-az plate mounting.

 

Comet 103 OTA.jpg



#7 fsphotography

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Posted 15 August 2017 - 09:06 AM

Hi guys,sorry for taking so long to reply, i'm on holidays at the moment traveling with my wife and our fifth wheeler.

I'll try and address some of the questions you have raised and add some-more information.

Stew,both lenses are 60mm not 40mm.  You say the ''comet'' was a 40mm scope, yet this 60mm scope fits perfectly into a case with a label that clearly says '' Comet NO 3''. Perhaps  the 40mm comet was a N01 or N02.? You tell me.

Chuck is correct in his observation and reasoning as to to the cell size and the tube size.

The discrepancy in the cell sizes is that the f15 is made of thin steel and non collimateble and the f20 cell is made of a brownish Bakelite and collimateble . The f20 cell is much larger and material thicker due to the fragility of the material its made of and the mechanics of the collimation feature. Hence the need for a larger tube for the extention.

I'm not at home so can't provide pics of lenses at this time,a description will have to do.

The f15 is an air spaced doublet,three spacers,most likely a Fraunhaufer, not coated. For its age,63 years minimum,its in very good condition, no scratches i can detect and only the slightest evidence of cleaning. Still a brilliant performer.

The f20 is a totally different animal and has me rather mystified.

When i was first offered this package i almost rejected it because of the condition of this lens. There was a dense scummy opaqueness between the two lenses and i had real concerns about fungal etching etc.

The rather unique feature of the of the interchangeable focal lengths proved too intriguing so i took the plunge and bought it.

Believe me i didn't get it for nothing,i'm not a gambler but i'm not against an educated punt.

Once it was in my hands i dismantled the lens with great trepidation, fearing the very worst.

To my great relief the scum wiped straight off with a little lens cleaner and a very soft cloth leaving two beautifully  polished surfaces.     .

The two elements  were surface to surface and appeared to be dead flat,no spacers,the first surface is convex as is the forth surface.

The first element,or crown?,is almost twice as thick as the second,the flint?.

The big surprise was that the first element or the''crown'' when viewed from the edge is a of a very green color,very close to window glass,my experience with any camera or telescope lenses is that the edge was always ''white'' or clear. Viewed front on the glass virtually disappears,

like looking into very deep clear pool of water. I really don't get this, i'm not at all familiar with this design of lens.

So,this lens had no spacers, should it have?  Is this a known design or an oddball Goto offering.

What is this green glass?

Disclosure,neither of these lenses is marked as ''GOTO''.  But i have seen other ''GOTO'' lenses on c.n.that were not marked.

Stew, you asked for any documentation with the scope, all that exists are the labels in the case. One states who made it and when and the other outlines what was in the box on delivery.

So, it might just be a Tasco.The only ''Goto'' logo on the scope itself is on the focuser.

The most interesting documentation,to me, is the penciled in name and address of one of the previous owners from the U.K.

''JAMES M LONG. F.R.A.S.     (FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY). I'm thinking that he knew his apples when it came to buying a telescope..

That's what convinced me to buy it.

Stew, the other bits and pieces you asked for pics of will have to wait until i get home.

Regards,

Frank.

 

                             .  

 

 

,  


Edited by fsphotography, 15 August 2017 - 09:21 AM.


#8 Stew44

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Posted 15 August 2017 - 09:35 AM

Frank,

 

The f/20 is a variation of a Cooke doublet.  See the Goto Optical Design thread here on CN for a discussion of the design.  It was used by Goto for their Kou or school telescopes.  Goto had better than 90% of the school telescope market in Japan and this lens design was that used.  The R2 is flat and the R3 is slightly concave.  We think it was pretty standard BK7 crown and F2 flint.  Definitely not the broad diffraction limited field of a Fraunhaufer design, but really the best that some of us have seen for planetary work.


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#9 Stew44

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Posted 15 August 2017 - 09:46 AM

The Comet 103 is a telescope manufactured from the 1930's to the late 1950's.  40mm and 750mm focal length.  If these are both 60mm then the f/15 is a Fraunhaufer and the f/20 is a variation on a Cooke doublet.  The f/20 is not named, but it's a Model 104 (alt-az) or a Model 105 (EQ). The f/15 is a Model 201 (alt-az) Uranus and a Model 202 (EQ) Eros.  Earlier tubes are larger than what we might think are needed as some are literally wrapped cardboard and also allow for easier handling?  It doesn't surprise me that a Uranus/Eros OTA might fit in a Comet case.  And given a little further info on it's background, the previous owner may have ordered the scope direct and customized it, and this was the best way to case it.  The bakelite is a surprise and very interesting.

 

You did say it came with a mount and likely that has two studs we can't see to go into the top plate of the simple alt-az.


Edited by Stew44, 15 August 2017 - 08:19 PM.


#10 Stew44

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Posted 15 August 2017 - 03:10 PM

And to answer the question about spacers - there on the f/15, not on the f/20, it's hard contact.



#11 fsphotography

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Posted 07 November 2017 - 01:51 AM

Hi all, sorry for  taking so long to get back to you with more pics of this f15/f20 ''GOTO''  60MM scope.

I have had the lens cells apart to check and clean, the f15 is an air spaced doublet and the f20 is a hard contact doublet.

The f15 as far as i can tell is of Fruanhaufer design,the f20 an odd design with the R1 being convex,the R2 flat,the R3concave and the R4 concave. The most odd thing to me is the bottle green front element of the F20. Both lens sets are almost pristine.

The tube is 2.5 mm thick and has two sets of threaded holes, two near the focuser end and two larger threaded ones at the lens end,one of them within mm's of the tube thread. That suggests to me that something is missing,whats your thoughts?

Frank.

Attached Thumbnails

  • goto f15.jpg
  • goto f20.jpg
  • In the box.jpg
  • focuser.jpg
  • focuser and finder scope.jpg

Edited by fsphotography, 07 November 2017 - 03:54 AM.

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#12 fsphotography

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Posted 07 November 2017 - 01:54 AM

And more .....

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  • lens cell #2.jpg
  • goto mount.jpg
  • goto crown and flint #1.jpg
  • goto crown & flint #2.jpg

Edited by fsphotography, 07 November 2017 - 03:55 AM.

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#13 fsphotography

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Posted 07 November 2017 - 01:56 AM

Last one.

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  • f20 lens cell.jpg

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#14 Stew44

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Posted 07 November 2017 - 06:48 PM

Thanks for posting the pics.  I have given this some thought since my last post on the scope.  First of all I believe this to be a Uranus OTA; an early Model 201.  The pair of holes toward the back of the scope if radial may be there to mount an adjustable altitude rod as shown in the picture following of my early post war Uranus.

 

PB070756.JPG

 

While the mount is similar as to mounting the OTA, look at the stoutness of my Uranus mount compared to your mount and simple altaz structure.  The legs are a lot smaller and frailer in build on yours.  I think your mount is an actual Comet mount.  I love the knob that locks altitude.  The mount is way too light for the Uranus OTA and it is really overloaded by the extended f/20 configuration.

 

I also note that the extension OTA is a different white finish than the Uranus OTA on your scope.  That makes me think that the f/20 modified Cooke doublet lens in cell may have been purchased along with the Uranus OTA and Comet altaz mount and an extension tube fashioned not by Goto, but perhaps the original owner.  The extension OTA case also isn't Goto.

 

The f/20 lens is a modified Cooke doublet.  It is the standard School telescope optic that Goto built their school sales around.  A discussion of the design is here

 

https://www.cloudyni...gn#entry8037318

 

As stated earlier I believe your accessories are typical, although I wonder why you have two erector lens assemblies from different periods.  That could open the door to the idea that this is a combination of two telescopes, but why the mount would be there from a third and so very lightweight as well is beyond me.  The finder is certainly typical Goto, and that makes this OTA later than mine, as mine didn't include a finder at the time it was sold.

 

Definitely lots to ponder.  You might post a couple pics of the holes in the OTA and enough of the OTA to determine placement.

 

 


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#15 Chuck Hards

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Posted 07 November 2017 - 07:09 PM

I was thinking that the non-black finish on the reducer coupling might also indicate an aftermarket modification.


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#16 fsphotography

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Posted 09 November 2017 - 01:59 AM

Thanks Stew and Chuck,

Stew,it might be an optical illusion, but to me the legs on both tripods look pretty much the same size. I've measured the timber(Oak i think) at 30mmx15mm. I don't think the mismatch in the paint color tells us any thing as it has been repainted by past owners. I am 

responsible for the white on the main ota, it was a badly painted blue when it came to me. The mount while looking too light works surprisingly well,it moves easily and stays where you put it,rather nifty. Somewhere on CN classic scopes I've seen an archival image of a Uranus on the same mount and tripod. The box for the extension is home made(rather badly)and i feel replaced a cardboard one that the f20 likely came in. The black erector was still sealed in a plastic sleeve when i got,never been used,i think its long length made it too awkward and the owner replaced it with the more practical chrome one. I had a look at the link you provided on the f20,quite informative, but doesn't reveal what glass was used. You didn't comment on the bottle green crown element so i'm assuming it's not that uncommon.                                                                                                                                                                                                                                            Chuck, I'm not sure what you are referring when you mention ''the reducer coupling''. Can you expand on that please? 

 

Frank.   


Edited by fsphotography, 09 November 2017 - 03:16 AM.

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#17 Stew44

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Posted 09 November 2017 - 11:01 AM

I think the long supports of each leg are likely the same dimensions.  However the spreaders are wider on the Uranus legs and the resulting triangular shape is more stable.

 

I forgot that the tube had been repainted when I posted, remembered after. 

 

Don't recall a Uranus on your mount.  There is a Comet on a homemade mount somewhat like yours and an Apollon, but no specific post that I am aware of.  More importantly the Uranus adverts show a mount like mine for early and a couple variants later with one having the altitude rod and the other very similar to the Unitron double knob adjustment.  I remain convinced that this is a Comet mount.

 

I have one of the black erector accessories and it is indeed long.  If you look at Dave Trotts video on his model 105, he shows it in terrestial mode and it's not too awkward to use.  Dave's videos are at the bottom of this link.

 

https://www.cloudyni...n-cn/?p=8054226

 

Glass for f/20 is BK7 crown and F2 flint, but not sure about your green element as to whether things might have changed.  I don't believe there is any mention of a green crown element in any discussion of this lens design in the school telescopes except for yours.

 

Not so much a reducer coupling, as the coupling piece that connects the f/20 extension tube to the cell threads on the Uranus tube.



#18 Chuck Hards

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Posted 09 November 2017 - 09:36 PM

Chuck, I'm not sure what you are referring when you mention ''the reducer coupling''. Can you expand on that please? 

Stew identified it, the connector between the two main tubes.  



#19 Stew44

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Posted 12 November 2017 - 12:47 PM

Okay, a new brochure just surfaced in a CN ad for a 1953 Uranus that changes my thoughts here.  Previously didn't understand the Comet "No.3" aspect of your scope.  This brochure shows a Comet 1,2 and a 3.  I now think that the Comet designation is the simple tripod head and not the 40mm aperture of the original Comet.  I think the Comet configuration is what you have as the base scope and the aperture is larger in the No.3.  The Uranus also in this brochure is on the older altaz mount and is likely the same OTA as your Comet No. 3.  Have asked the seller to provide better images of the brochures.  Hopefully he will.

 

brochure Goto 1953.jpg


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#20 Terra Nova

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Posted 13 November 2017 - 09:28 AM

My question is address to the telescope in the original post. How can that mount possibly accomodate serious astronomical use of that telescope, especially when it is in F20 mode. I can’t even imagine how such a mount without slow-motions and a stablizer bar could be practical. The OTA becomes one giant lever on that pivot!



#21 Stew44

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Posted 13 November 2017 - 02:22 PM

My question is address to the telescope in the original post. How can that mount possibly accomodate serious astronomical use of that telescope, especially when it is in F20 mode. I can’t even imagine how such a mount without slow-motions and a stablizer bar could be practical. The OTA becomes one giant lever on that pivot!

That mount was for the the original 40mm Comet and not likely suitable for a larger OTA such as the Comet No. 3 appears to be.  And I believe the school f/20 lens and extension to be an add-on adaptation by a previous owner from a second telescope set (hence two image erector assemblies).  The OP states the mount adequate/stable with even the f/20 in place.


Edited by Stew44, 13 November 2017 - 03:56 PM.

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#22 Chuck Hards

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Posted 13 November 2017 - 07:46 PM

Terra's post hints at a similar thought-process that may have happened at Goto, when they designed their equatorial mounts.  Rugged, massive, not the minimalist aluminum castings of the competition that came afterwards.  They could have had a bad taste in their mouth from possibly under-performing, simple alt-az school mounts, resulting in the wonderful equatorials they produced.  scratchhead2.gif  


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#23 fsphotography

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Posted 13 November 2017 - 11:47 PM

I can understand the doubts about this mounts that Terra expresses ,it looks all wrong for a start. But,despite how it looks and the rather puny pivot point it works rather well,keep in mind that it would not have been intended for the f20 extension. Surprisingly even in f20 mode

you can set it at any elevation,even horizontal,and it will stay put with just a little more tension on the locking screw while still allowing movement. I must take the mount apart one day and see what it is they have used as the clutch bearing surface. After all that would i use the mount for serious viewing, not really,i piggyback the scope on the TSA 102 mounted on the AZ-HEQ 6.

Stew, the new GOTO  brochure images you have come up with are very interesting as they positively identify my scope as a COMET No3,as stated in the carry case. I have to disagree with you on your theory that the COMET No 3 and the URANUS are the same ota, the pictures show that the URANUS connects to the mount much closer to the centre of the tube than does the COMET,and that the lens hood is longer on the URANUS, nit picking i know, but perhaps that's the only difference.

I think the jury is still out on the question of the f20 extension,i have examined the interior of both the f15 and f20 tubes and find that the finish/surface of both tubes is practically identical suggesting to me that they were both made by the same people. Both tubes have been repainted externally more than once so there are no clues there. The idea has occurred to me,Stew you almost suggested the same,,that perhaps a past owner had an f20 as well,the tube became damaged and in a Eureka moment killed two birds with one stone.So,the question is,was this f15/f20 marriage a GOTTO factory thought bubble that wasn't continued with,or a rescue?

I'm guessing that the work either way was carried out by the GOTTO factory which is supported by the quality of the workmanship and fit. But i could be totally wrong.

Chuck,you are quite correct re the reducer coupling,i had a little scratch around and found it indeed was once black,so black it shall be once again. I think you are most likely spot on about the GOTO mounts too.

 

Frank.


Edited by fsphotography, 14 November 2017 - 05:18 AM.

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#24 Stew44

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Posted 14 November 2017 - 09:13 AM

Frank, the biggest distract-er to this being a Goto product pairing is the poorly done extension case.  I have seen Goto do nice wooden cases for even the very least expensive of their telescopes.  I find it hard to believe that this is an offering from Goto with a case as you have described.  And on the workmanship of the coupling, I can't help but admire ATM efforts over the long haul.  I believe of the two possibilities, it is the rescue effort of the f/20 scope that best fits the data.

 

Whatever, it's still a nice pairing and mounted appropriately on modern mount, killer pairing as well.




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