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W. Ottway Achromat Objective Disassembly

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#1 kirving

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Posted 15 April 2024 - 12:26 AM

Hi all, I'm new to this forum but hoping I might be able to get some advice.

 

I recently bought a 1920's W. Ottway 5-15X zoom telescope at an antique fair, and I'm trying to do a restoration as it's tarnished, and the grease has dried up.

 

Unfortunately, the front objective is tarnished and the two elements are delaminating. I've got almost all of the scope apart, which which has been a challenge, with very tight maching tolerances and no instructions, but I'm stuck here.

 

To explain the picture, I can see through the notch at the 12 o'clock position, that the diameter of the lens is probably 2mm wider diameter than both the front and rear brass diameter - so I'm sure it's not a interference fit alone.

 

My problem is. I can't find any join point if two separate pieces of glass are being used. The radially drilled holes I think are only used in conjunction with another offset piece, to set centration of the element.

 

Has anyone come across this design before, and how might I split this open to clean and re-glue the elements?

 

Thank you!

 

 

 

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#2 DAVIDG

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Posted 15 April 2024 - 10:01 AM

 Old lens like this are usually not cemented but air spaced. It looks to me that moisture is between the elements.  The usual method to hold a lens in place is with a retainer ring.  Either it is threaded and is screwed in place or slides in place and is held by screws or pins.  I also see what looks to be a part line  in the middle of the side of cell. So it possible that the cell is made of two pieces that unscrews from each other. 

 

 

                     - Dave 


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#3 davidc135

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Posted 15 April 2024 - 10:43 AM

I'd try soaking everything in white spirit.  David



#4 kirving

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Posted 15 April 2024 - 12:01 PM

 Old lens like this are usually not cemented but air spaced. It looks to me that moisture is between the elements.  The usual method to hold a lens in place is with a retainer ring.  Either it is threaded and is screwed in place or slides in place and is held by screws or pins.  I also see what looks to be a part line  in the middle of the side of cell. So it possible that the cell is made of two pieces that unscrews from each other. 

 

 

                     - Dave 

For other elements in the telescope, the retainer rings are much more obvious, but not here. Normally, threaded sections are longer than necessary to accommodate tolerances, or an o-ring might be used, but not here as far as I can work out. 

 

I'm guessing the XI marking was done by a previous restore attempt, as opposed to the original assembler? Or would those marks be common do you know? That might indicate that the wider diameter part is a separate piece if so.

 

Thanks for the info on the air-gap - if it were just condensation I'd try to dry it out, but its also looks yellow potentially due to some glue or dirty water leeching in.

 

There does seem to be a split line in the middle but it becomes invisible for a section. The inner and outer diameters are not concentric, but so it may also be a machining mark (there are plenty others - they look to have stuck to tolerances were is mattered, and other sections are rough enough. Normally threads are longer than necessary to account for tolerance's, but if it were to split in the middle here, I'm not sure where the tolerance would be taken up.

 

I've had great success with a strap wrench so far, but I think it'll need to buy/make jaws for a vice which will hold this more securely.

 

I'd try soaking everything in white spirit.  David

Will give that a go too, thanks, it might soften things up.



#5 davidc135

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Posted 15 April 2024 - 01:43 PM

Are those spacers that can be seen, supporting the air-spaced view? Although I don't know why there are more than three.

 

It may be that external tarnish has improved the lens, acting as an AR coating.

 

What is the aperture?

 

David



#6 ccwemyss

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Posted 15 April 2024 - 09:05 PM

This might be a case where it's worth sending it to Cory Suddarth.

 

Chip W. 



#7 kirving

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Posted 18 April 2024 - 06:43 PM

Are those spacers that can be seen, supporting the air-spaced view? Although I don't know why there are more than three.

 

It may be that external tarnish has improved the lens, acting as an AR coating.

 

What is the aperture?

 

David

It's around 60mm I think - not with me at the moment.

 

The first photos weren't great - much more visible in the photo below. It's certainly an air gap, but on the spacers, I'm not really sure. There are 4 in total, but look more like machined flat areas, but again I'm not sure.

 

This might be a case where it's worth sending it to Cory Suddarth.

 

Chip W. 

 I had a look at his website which does look really impressive. I work in camera/optics manufacturing so am very familiar with much of the tools and processes, so kinda thought this might be a nice project for me. It's really for an ornament, and holds no sentimental value for me, and isn't worth much money either - so I'll have to see how much money I want to put into it.

 

But thank you for the tip!

 

 

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