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Takahashi FC-100 from Zen-Ugh

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#51 Derek Wong

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Posted 23 May 2022 - 01:56 PM

Hi Steve:

 

I am not on CN any more due to time but I did see your post.  Here is some info (including the posts following my question):

 

https://www.cloudyni...here/?p=6343780

 

The lesson is that pre-1987 Tak flourite doublets (not FCT) can have cloudy flint elements.  The best way is to avoid buying them because even if they are clear, they could get cloudy in the right environment.  There were regrinding shops for these lenses in Japan but those services are gone.  If your hail Mary doesn't work you may need to replace the element but the glass may not be available.

 

Derek


Edited by Derek Wong, 23 May 2022 - 02:06 PM.

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#52 ccwemyss

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Posted 23 May 2022 - 03:54 PM

I had an early FC-100 with similar fogging and contacted Tak for any solution last year. They told me essentially following

 

"the equipment for re-polishing the lens and re-coating at that time has already been lost. Therefore, with Takahashi's old refracting telescope, maintenance of the optical system is only cleaning and optical axis adjustment." 

 

James

Say what you will about the prices for AP scopes, but when the coating on the front of my oil-spaced 6" f9 NASA glass triplet from 1985 started to go, Roland said, "Send it in and I'll repolish it." Certainly not a scope for which original tooling was still in the shop. The cost was quite reasonable. 

 

Chip W. 


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#53 Lagrange

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Posted 23 May 2022 - 08:34 PM

Say what you will about the prices for AP scopes, but when the coating on the front of my oil-spaced 6" f9 NASA glass triplet from 1985 started to go, Roland said, "Send it in and I'll repolish it." Certainly not a scope for which original tooling was still in the shop. The cost was quite reasonable. 

 

Chip W. 

I think the other problem is that while you might be able to find someone to re-polish and re-coat an element where the coating has started to go, it's a much bigger challenge when the glass itself is the issue. When that happens you really need a new element.

 

There was a post on CN a few years ago where Hiromu (n2068dd) had asked Tak's optical designer Mr Yayama about their switch back to FC doublets after years of offering FS designs. He mentioned that the new fluorite elements are the same design as the ones in the old FC scopes, so it's possible to replace an old fogged FC front mating element with one of the new ones that are used in the current FC models.

 

Would be worth checking with Tak if this is an option for this particular scope.


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#54 davidc135

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Posted 24 May 2022 - 02:11 AM

I think the other problem is that while you might be able to find someone to re-polish and re-coat an element where the coating has started to go, it's a much bigger challenge when the glass itself is the issue. When that happens you really need a new element.

 

There was a post on CN a few years ago where Hiromu (n2068dd) had asked Tak's optical designer Mr Yayama about their switch back to FC doublets after years of offering FS designs. He mentioned that the new fluorite elements are the same design as the ones in the old FC scopes, so it's possible to replace an old fogged FC front mating element with one of the new ones that are used in the current FC models.

 

Would be worth checking with Tak if this is an option for this particular scope.

I see the FC-100DZ is F/8 so maybe there is an exact match for the front element.  David


Edited by davidc135, 24 May 2022 - 02:25 AM.


#55 Lagrange

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Posted 24 May 2022 - 01:25 PM

I see the FC-100DZ is F/8 so maybe there is an exact match for the front element.  David

It would be the obvious candidate, but the post where I read that information was from 2017 while the DZ was launched in 2019 so I assume Mr Yuyama was referring to the mating element from the FC-100DC/DF. Obviously they have a shorter focal ratio to the original FC being f/7.4, so presumably an original FC refurbished this way would end up with a 740mm focal length too?



#56 Steve_M_M

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Posted 24 May 2022 - 05:29 PM

Well, to put a stamp on this...I tried various different methods over the past few days.  Some involving heating and other ideas.  I also tried sulfuric acid.  First 30 minutes, then 2 hrs, and just now I pulled it out after 18 hours heated.  Nothing.

 

As can be seen form some the old posts that were linked above, the issue appears to be the glass.  And, best I can tell, if it is polished/resurfaced, it will not be very good.

 

I spoke to a very helpful person at TNR.  She was passing my issue along to their support group who was to get back to me with either a solution or cost of a new element and installation.  Unfortunately, it has been a week and I have not heard anything.  I will follow up again.


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#57 davidc135

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Posted 24 May 2022 - 07:17 PM

I had an early FC-100 with similar fogging and contacted Tak for any solution last year. They told me essentially following

 

"the equipment for re-polishing the lens and re-coating at that time has already been lost. Therefore, with Takahashi's old refracting telescope, maintenance of the optical system is only cleaning and optical axis adjustment." 

 

James

Ccwemyss also re-posted the above. If there was a replacement front element available Takahashi would surely have mentioned it.  David


Edited by davidc135, 24 May 2022 - 07:18 PM.


#58 Lagrange

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Posted 24 May 2022 - 09:14 PM

Ccwemyss also re-posted the above. If there was a replacement front element available Takahashi would surely have mentioned it.  David

You would think so, and since James700 is located in Japan he would have asked directly rather than going through a distributor or retailer.

 

Perhaps element replacement was one of those ideas that was floated but never went anywhere. It might be worth Steve sending a PM to Hiromu (n2068dd) anyway since he was the one who mentioned it a few years ago, just to ask if he'd ever heard of it being done or knew how to make a special request of that kind.


Edited by Lagrange, 24 May 2022 - 09:16 PM.


#59 davidc135

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Posted 25 May 2022 - 01:58 AM

 

 

As can be seen form some the old posts that were linked above, the issue appears to be the glass.  And, best I can tell, if it is polished/resurfaced, it will not be very good.

 

 

Are both surfaces of the front element affected? I can see that the second is very bad. If the first surface is in decent shape after getting on for forty years I'd think that, with reasonable care and the Texas climate, the re-worked objective should give many years of good service.

 

The re-worked lens should behave just as well as the original but it depends on what's involved and the cost and if it's worth it.

 

David



#60 Terra Nova

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Posted 25 May 2022 - 07:21 AM

I seriously doubt that it would be possible to get a single element replaced and having it perform as it should. Given the exceedingly fine optical tolerances that Takahashi fluorite apos are know for, I would imagine that elements are matched during final polishing and testing. It seems the only recourse would be to find a replacement objective, an expensive proposition for such an old scope. I’d heard stories about lens deterioration in the older ‘grey-series’ Taks. The only ones I’ve had (still have) are the later green-trimmed ones. My 1997 still looks pristine.


Edited by Terra Nova, 25 May 2022 - 07:24 AM.

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#61 tim53

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Posted 25 May 2022 - 08:25 AM

I seriously doubt that it would be possible to get a single element replaced and having it perform as it should. Given the exceedingly fine optical tolerances that Takahashi fluorite apos are know for, I would imagine that elements are matched during final polishing and testing. It seems the only recourse would be to find a replacement objective, an expensive proposition for such an old scope. I’d heard stories about lens deterioration in the older ‘grey-series’ Taks. The only ones I’ve had (still have) are the later green-trimmed ones. My 1997 still looks pristine.

This probably calls for refiguring or generating a new element and dpac testing as you go.  


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#62 Terra Nova

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Posted 25 May 2022 - 09:05 AM

This probably calls for refiguring or generating a new element and dpac testing as you go.  

Tim, as I understand it, Steve and others indicate that the problematic haze is in fact in the glass rather than on it. That being the case, no amount of refiguring is going to help. It would require grinding and polishing a new one from a blank.


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#63 tim53

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Posted 25 May 2022 - 10:24 AM

I’d do it if it were mine. Have I ever made a lens before?  No. Sounds like a lot of fun, though. 


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#64 davidc135

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Posted 25 May 2022 - 01:50 PM

Tim, as I understand it, Steve and others indicate that the problematic haze is in fact in the glass rather than on it. That being the case, no amount of refiguring is going to help. It would require grinding and polishing a new one from a blank.

In post 43 Steve mentions that the spacers left clear windows of protected clear glass so, hopefully, under the damaged surface layer the glass is OK.

 

With a careful approach and a little ATM experience lenses aren't so different to mirrors. Not a job for a beginner, though.

 

David


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#65 Terra Nova

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Posted 25 May 2022 - 03:11 PM

In post 43 Steve mentions that the spacers left clear windows of protected clear glass so, hopefully, under the damaged surface layer the glass is OK.

 

With a careful approach and a little ATM experience lenses aren't so different to mirrors. Not a job for a beginner, though.

 

David

Thanks. I was going by his statement:

 

“As can be seen form some the old posts that were linked above, the issue appears to be the glass.  And, best I can tell, if it is polished/resurfaced, it will not be very good.“- #56.
 


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#66 semlin

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Posted 25 May 2022 - 03:35 PM

Well, to put a stamp on this...I tried various different methods over the past few days.  Some involving heating and other ideas.  I also tried sulfuric acid.  First 30 minutes, then 2 hrs, and just now I pulled it out after 18 hours heated.  Nothing.

 

As can be seen form some the old posts that were linked above, the issue appears to be the glass.  And, best I can tell, if it is polished/resurfaced, it will not be very good.

 

I spoke to a very helpful person at TNR.  She was passing my issue along to their support group who was to get back to me with either a solution or cost of a new element and installation.  Unfortunately, it has been a week and I have not heard anything.  I will follow up again.

have you tried muriatic acid?

 

i used it to clean hazed 100 year old windows at our old house.  they were behind ancient bug screens and not washed for decades and nothing budged the mystery haze which we theorized was mineral build up from rain.  at the suggestion of a hs chemistry teacher we used muriatic acid mixed with distilled water and it took it off so they looked like new.  

 

i do not recall the concentration but he started with a very low ratio and kept adding acid until it worked.  

 

some dimly recalled tips keeping in mind i am not a chemist!  no recourse!

 

1.  always put the water in the jar before the acid to avoid offgassing.  also, the water ratio is key. muriatic acid will not work alone.

 

2.  use a paint brush to work the acid solution on the glass.  when you have it right there was a chemical reaction where it forms a froth as you work it in and the haze just vanishes.

 

3.  rinse it first with distlled water and bicarbonate to neutralize the acid, then again with straight distilled water.  we used two spray bottles to rinse and wiped that off with two cloths.  most times it took two or three rounds of applications to fully clear the glass.



#67 Terra Nova

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Posted 25 May 2022 - 03:47 PM

have you tried muriatic acid?

 

i used it to clean hazed 100 year old windows at our old house.  they were behind ancient bug screens and not washed for decades and nothing budged the mystery haze which we theorized was mineral build up from rain.  at the suggestion of a hs chemistry teacher we used muriatic acid mixed with distilled water and it took it off so they looked like new.  

 

i do not recall the concentration but he started with a very low ratio and kept adding acid until it worked.  

 

some dimly recalled tips keeping in mind i am not a chemist!  no recourse!

 

1.  always put the water in the jar before the acid to avoid offgassing.  also, the water ratio is key. muriatic acid will not work alone.

 

2.  use a paint brush to work the acid solution on the glass.  when you have it right there was a chemical reaction where it forms a froth as you work it in and the haze just vanishes.

 

3.  rinse it first with distlled water and bicarbonate to neutralize the acid, then again with straight distilled water.  we used two spray bottles to rinse and wiped that off with two cloths.  most times it took two or three rounds of applications to fully clear the glass.

Check out post #35 above. :lol:


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#68 semlin

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Posted 25 May 2022 - 06:06 PM

Check out post #35 above. lol.gif

d'oh.  i mentioned i was not a chemist.


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#69 Lagrange

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Posted 25 May 2022 - 06:38 PM

Many optical glasses are not particularly acid resistant (unlike Pyrex or standard crown glass) so I'd be very hesitant to use strong acids of any kind for cleaning unless I knew the glass type and could check if it was safe or someone else had tried it successfully.



#70 stmarch

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Posted 27 May 2022 - 09:47 AM

I have some experience working with different  chemicals including acids. 

FIRST. I hope anyone using chemicals, especially acids is using personal protective equipment like nitrile gloves. Safety glasses, clothing cover, and a proper work area.

 

As seen. Sulfuric and Hydrochloric acids won't have much effect at room temperature. HCL will have a little effect under heat.

What will remove any coating and/or glass is Hydrofluoric acid, since it can etches glass. This acid is very dangerous to work with.  It should only be used by those who are experienced and under a chemical work bench with fume hoods.

However to attempt on the glass lens in question, IMHO only if no other option was available. Then only by someone who is familiar with using HF on glass. 


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#71 Steve_M_M

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Posted 27 May 2022 - 10:08 AM

I have some experience working with different  chemicals including acids. 

FIRST. I hope anyone using chemicals, especially acids is using personal protective equipment like nitrile gloves. Safety glasses, clothing cover, and a proper work area.

 

As seen. Sulfuric and Hydrochloric acids won't have much effect at room temperature. HCL will have a little effect under heat.

What will remove any coating and/or glass is Hydrofluoric acid, since it can etches glass. This acid is very dangerous to work with.  It should only be used by those who are experienced and under a chemical work bench with fume hoods.

However to attempt on the glass lens in question, IMHO only if no other option was available. Then only by someone who is familiar with using HF on glass. 

Yes, I had all my PPE (my sons call it my mad scientist outfit) on for the acids I tried.  I am at the point of trying anything, but HF would be out of my league.  

 

As for the comments about "on the glass" or  "in the glass".  I believe this to be "on the glass".  Some of the posts linked indicate it is "in the glass" or it is the glass itself.  What I can't tell is how deep the "on the glass" goes.  Maybe it's on and in, LOL.  

 

Going all the way back to day 1 when I bought this....I was surprised no one in Japan bid on a $750 FC-100 with a ton of accessories.  Maybe in Japan they already know these damaged older FC-100's are toast and cannot be repaired under any circumstances.


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#72 Terra Nova

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Posted 27 May 2022 - 10:42 AM

Yes, I had all my PPE (my sons call it my mad scientist outfit) on for the acids I tried.  I am at the point of trying anything, but HF would be out of my league.  

 

As for the comments about "on the glass" or  "in the glass".  I believe this to be "on the glass".  Some of the posts linked indicate it is "in the glass" or it is the glass itself.  What I can't tell is how deep the "on the glass" goes.  Maybe it's on and in, LOL.  

 

Going all the way back to day 1 when I bought this....I was surprised no one in Japan bid on a $750 FC-100 with a ton of accessories.  Maybe in Japan they already know these damaged older FC-100's are toast and cannot be repaired under any circumstances.

That could very well be the case. Taks are far more common in Japan than they are here and have been for a very long time. And also they are well familiar with the humid maritime subtropical climate over there and its effects on many things, not just telescopes. So yeah, these older Taks probably have a rep for this sort of thing in Japan. As far as Hydrofluoric acid, I don’t see the point in its use, even as a last resort. It would ruin the glass, that much is a known fact. 


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#73 semlin

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Posted 27 May 2022 - 11:09 AM

Yes, I had all my PPE (my sons call it my mad scientist outfit) on for the acids I tried.  I am at the point of trying anything, but HF would be out of my league.  

 

As for the comments about "on the glass" or  "in the glass".  I believe this to be "on the glass".  Some of the posts linked indicate it is "in the glass" or it is the glass itself.  What I can't tell is how deep the "on the glass" goes.  Maybe it's on and in, LOL.  

 

Going all the way back to day 1 when I bought this....I was surprised no one in Japan bid on a $750 FC-100 with a ton of accessories.  Maybe in Japan they already know these damaged older FC-100's are toast and cannot be repaired under any circumstances.

i think there is a good chance the haze "is" the coating.  so not in the glass, but chemically bonded to it.

 

if the problem is more common in japan, then it is likely humidity caused the issue or perhaps humidity plus maybe pollution given how industrialized japan is.  sulfur dioxide and nitrogen dioxide are typical acid rain pollutants.


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#74 tim53

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Posted 27 May 2022 - 01:07 PM

I'd still be tempted to try to re-polish the lens, but you'd need to set it up in a test apparatus where you could quickly remove and replace the lens as you progress.

 

I suspect that Tak doesn't want to work on it for reasons similar to Meade and Celestron being reluctant to work on old or unusual telescopes - it's more labor-intensive for them than it's worth.  Celestron, for example, not only would not sell me a corrector for my C-14 prototype (even when I told them I would refigure the secondary myself), they wouldn't let one of their retailers sell me one either.  In the case of an SCT, there's really nothing particularly "magical" about the optics, so if the end user is knowledgeable enough about the optics work involved, and willing to spend the time it takes (that a commercial production outfit can't afford to).  In japan, in particular, it probably makes even less sense for them to work on old optics, since they're much more common there.


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#75 davidmcgo

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Posted 27 May 2022 - 01:28 PM

With nothing to lose at this point, have you considered Meguiar’s PlastX headlight polish?  It works very well to clear up the cloudy deposits that form on the blue glass element in my Lunt BF1200 diagonal that don’t come off with solvents, and has not caused any noticeable scratching in quite a few cleanings.

 

I use a tissue to wipe on, let dry then buff with another tissue.  The deposits form on the tinted glass so it isn’t an interference filter with coatings that fail like the PSTs.

 

Dave


Edited by davidmcgo, 27 May 2022 - 01:30 PM.

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