Author Topic: Restoration of Dollond refractor  (Read 1218 times)

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Roberto

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Restoration of Dollond refractor
« on: Oct 05, 2020, 11:00:10 »
Hello All

As some of you may remember, Roy wrote to members in July alerting them to an old telescope being offered to the society.  I spoke to Roy and told him I was interested to look at it as it seemed like a good restoration project.
I picked up the telescope in mid-July from a gentleman in Bromley.  I didn't push him to give me much information on the scope as he seemed to be keen to be rid of it.  He did say he had had it for a long time but that it had sat unused for years.  Below some pictures of the original as it was offered to Roy:



The tripod is huge; legs alone are 68" long!



This last picture, as received in the original email from Roy, piqued my interest:



You can barely see the brand of Dollond!   I looked up "Dollond 3" refractor" in Google and this thread on CloudyNights from 2010 by Neil English turned up...it seemed like the same model:

https://www.cloudynights.com/topic/262383-a-dollond-3-f15-refractor/

As I'm sure you all know, (John) Dollond is reputedly the inventor of achromatic telescopes (doublets and then triplets), so this could potentially be a telescope with a pedigree!

Neil English's thread talks about a Student model. His was branded as such, had a serial number and the OTA was painted green.

First impressions

I got the scope and monster tripod home, cleaned it a bit to discover that it was not grey or green but black (with greenish legs for the tripod) and that the lens was, fortunately, in very good shape.
At the time I only looked at some distant trees through it and it seemed well corrected for what I suspected to be a doublet (obviously helped by its long focal length).  The tube had a dent on the underside but otherwise all mechanical parts seemed to work well and the focuser was not bent or jammed. 



I put the scope away and told myself I should start working on it soon...

Tripod and mount restoration

Too busy doing nothing I only managed to look at the scope late last month and started by stripping the tripod into parts and cleaning it thoroughly:



I removed all rust from the legs, screws, nuts, chains, etc:



Since there was significant rust on the tripod and pitting building in the brass parts, I decided to strip any old paint on the tripod and fully polish the brass parts.  I also decided to paint the tripod with satin black spray paint as I knew the OTA was also black:



After using Renaissance Wax on the polished brass and painted/lacquered surfaces, I put the tripod together earlier this month:



The alt-az mount is simple yet very smooth to operate:



And another one:



OTA restoration

The OTA was originally finished in wrinkled black paint.  I thought about repairing the dent from inside but three baffles inside the tube prevented me from trying to reach it from outside.  In the end, I decided to use metal filler and try to replicate the textured finish as best as I could.

First some pictures of all parts as I disassembled them showing they were in overall good shape but heavily tarnished.  Pitting was present but mostly superficial and it polished out well.

Focuser and finder end:


Internal baffling:


Lens cell:


OTA length:


The end at the other end of the business' end:


Finder:


What I thought was a barlow but later confirmed to be a pancratic eyepiece:


After some "elbow grease", finder and pancratic eyepiece looked like this:


Pancratic eyepiece is labelled Broadhurst Clarkson & Co, 63 Farringdon Rd which makes it post 1908 when the name was adopted.


Focuser pinion showing old dried up grease:


And focuser parts:


Voila!




Some antique telescope experts will no doubt scream that I should not have polished the parts to this degree but I was worried about pitting becoming worse and not being able to use the telescope outside for fear of further oxidation.

I painted the OTA over the weekend during a (very) short spell of dry weather:



And started reassembly:


Which ended up looking like this...





The lens

I was hoping for a triplet ...



...but it is confirmed as a doublet by laser reflections:


Upon removal of the cell, it was clear that the elements had rotated but there was no fungus or damage:



Peter Ceravolo on CloudyNights where I started another thread about this restoration suggested that this is an "edge contacted" doublet as it does not have any spacers between elements.

I have cleaned the three other eyepieces that came with the scope.  Two are of the same vintage and a third, labelled BC&Co, seems to be newer.

I am waiting for sunnier weather to put the scope together and take some proper pictures to show everyone. Hopefully it won't be long before we can meet again and I can bring it to the Hall for all to see!

Roberto



MarkS

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Re: Restoration of Dollond refractor
« Reply #1 on: Oct 05, 2020, 13:54:12 »
Wow!  What a great project!

Thanks for all the pictures showing your excellent progress.  I'm looking forward to seeing it sometime.

Mark

Rick

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Re: Restoration of Dollond refractor
« Reply #2 on: Oct 05, 2020, 14:22:26 »
Good work. :)

The Thing

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Re: Restoration of Dollond refractor
« Reply #3 on: Oct 05, 2020, 21:04:28 »
That is a lovely scope Roberto. I hope you have hours of great observing with it to make up for the hours of restoration.
We're all guinea pigs in the laboratory of life. Better a fluffy guinea pig than a lab rat!
¯\_(ツ)_/¯ (Gallic shrug :))

Hugh

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Re: Restoration of Dollond refractor
« Reply #4 on: Oct 06, 2020, 08:22:32 »
Hi Roberto

Having had an opportunity to see the scope before Roy passed it on, may I agree what a marvelous job you have done in the restoration!  A very worthy personal effort on behalf of the previous owner and astronomy as well to recover the instrument.

A nicely recorded pictorial record of the process as well!

Thanks

Hugh

Roberto

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Re: Restoration of Dollond refractor
« Reply #5 on: Oct 06, 2020, 09:44:44 »
Thank you all for the words of encouragement.  I hope this telescope can be used by the Society when we are back to normal.  I may even attend my first session at Otford with it! 
I will most likely machine an eyepiece adaptor to use modern eyepieces as the original ones are not up to the standards of the main objective.

Roberto

Carole

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Re: Restoration of Dollond refractor
« Reply #6 on: Oct 06, 2020, 10:31:03 »
Excellent job Roberto.

I wonder if the previous owner might like to see the restoration project or was he completely disinterested and just wanted to get rid of it?

Carole

Roberto

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Re: Restoration of Dollond refractor
« Reply #7 on: Oct 06, 2020, 11:50:45 »
Hi Carole

Thank you.  I promised some pictures to him and will send him those.  I did not talk to him much when I picked up the scope.  He wasn't much into it, we were coming out of the full lockdown (if we ever did) and he was wearing a jacket with signs of XR (extinction rebellion) and I didn't want to get into an argument and walk away without a scope!

Roberto

julian

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Re: Restoration of Dollond refractor
« Reply #8 on: Oct 06, 2020, 15:03:14 »
That looked like a fun project to do and it came out very nice.

NoelC

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Re: Restoration of Dollond refractor
« Reply #9 on: Oct 07, 2020, 17:09:03 »
Looks Great Roberto
Lovely job!
Is that a lathe in the background?

Noel
Synta mount, a bunch of telescopes and a shed (on wheels).

Roberto

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Re: Restoration of Dollond refractor
« Reply #10 on: Oct 07, 2020, 17:18:37 »
Hi Julian, Noel  - Thank you!

Noel, yes it's a Colchester Student lathe from 1967.

Roberto

Roberto

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Re: Restoration of Dollond refractor
« Reply #11 on: Oct 11, 2020, 17:26:51 »
Right...more progress and some finality to this project!

I resumed by trying to restore the box but I am no carpenter and do no wood work.  The bottom of it was rotten at one end.  I sanded away the rot and filled with wood filler trying to get as close to the original colour as possible (difficult). After the whole box had been sanded, I cleaned it inside and removed the old felt:



After some work, here's how it looks:



And after staining the wood, waxing and polishing it some more:



I still don't know what type of wood it is; very likely early 20th century:





I also cleaned and restored - by painting and polishing - the eyepieces:



All together now:



And inside:

« Last Edit: Oct 12, 2020, 12:29:32 by Roberto »

Roberto

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Re: Restoration of Dollond refractor
« Reply #12 on: Oct 11, 2020, 17:30:03 »
Outside before it rains!



Another one:



Some close-ups:








Roberto

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Re: Restoration of Dollond refractor
« Reply #13 on: Oct 11, 2020, 17:31:44 »
As I said, I suspect the lens is well corrected.  I have not had a chance to try it under the stars yet but here are a couple of snaps through one of the eyepieces:





Once I machine an adpater for modern eyepices, I may put a webcam through it and will image a star and its diffraction rings.

Roberto

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Re: Restoration of Dollond refractor
« Reply #14 on: Oct 11, 2020, 17:32:48 »
To another 100 years of use:



Roberto