158 replies to this topic

[ccwemyss]

Have you tried acetone? 

 

Chip W. 

[Steve_M_M]

Yes. 
 

iso 91, hydrogen peroxide, bleach, acetone, lemon juice, scrubbing bubbles.  Maybe I’ll try paint remover or oven cleaner tomorrow. 

Edited by Steve_M_M, 20 May 2022 - 09:46 PM.

[davidc135]

After hitting it with everything you could imagine.  No change. 
 

I have not heard back from TNR about a possible replacement lens.  Based on the last couple posts, there is nothing available. 

Does it affect views? It looks as if it would. Are both sides affected?

 

If the effect is superficial and if there is nothing unusual about the type of glass used it could be a straightforward job for an optician or advanced amateur to repolish the lens and test in conjunction with its fluorite partner. The glass type should be known in case there are any special requirements in working or coating, if that's required.

 

If only polishing/figuring is needed then just a simple pitch lap needs to be made but, if damage extends into the glass then regrinding would require an expensive tool and test plate. Hopefully the glass surface is intact if you check with a x10 magnifier eg a 25mm Kellner or Plossl back to front.

 

If the alternative is replacing the objective then it would be worthwhile contacting optical shops in the US for quotes if the glass research turned up no problems. Also there are amateurs on CN with lens experience.

 

Good luck!  David

Edited by davidc135, 21 May 2022 - 02:57 AM.

[davidc135]

I found some flourite objective designs that used either K5 glass (very resistant to attack) or K7 glass. Over a period of time K7 is fairly liable to corrosion by water vapour in warm, humid conditions forming a milky film which cannot be wiped off. That could be it. Otherwise an average glass.

 

David

Edited by davidc135, 21 May 2022 - 02:56 AM.

[GUS.K]

Yes. 
 

iso 91, hydrogen peroxide, bleach, acetone, lemon juice, scrubbing bubbles.  Maybe I’ll try paint remover or oven cleaner tomorrow. 

Steve, CLR cleaner has been used by some solar scope owners to remove some deposits from Lunt solar blocking filters, I don't know if it can help or not or even if it's safe to use on a coated glass lens, or if it will do anything at all in your situation, just putting it here for reference-  https://www.cloudyni...g-power-of-clr/

[deSitter]

Since this is just normal glass, I don't see why it would not be possible to analyze the figure and just repolish this one element. Someone like our Dave Groski could probably make short work of such a project. It seems such a shame - this is the one problem that will ruin the image for sure - anything else, clams, flaking coatings, scratches, pits, would all produce likely no visible deterioration.

 

-drl

[Steve_M_M]

Steve, CLR cleaner has been used by some solar scope owners to remove some deposits from Lunt solar blocking filters, I don't know if it can help or not or even if it's safe to use on a coated glass lens, or if it will do anything at all in your situation, just putting it here for reference-  https://www.cloudyni...g-power-of-clr/

At this point I am not worried about the coating if it came off evenly.  So, I tried CLR this morning.  Same result   Thanks for the suggestion!  I had not thought of that one.

[Steve_M_M]

Since this is just normal glass, I don't see why it would not be possible to analyze the figure and just repolish this one element. Someone like our Dave Groski could probably make short work of such a project. It seems such a shame - this is the one problem that will ruin the image for sure - anything else, clams, flaking coatings, scratches, pits, would all produce likely no visible deterioration.

 

-drl

Agreed.  And this issue not only ruins the image, there is a huge loss of light passing through.

[Terra Nova]

I found some flourite objective designs that used either K5 glass (very resistant to attack) or K7 glass. Over a period of time K7 is fairly liable to corrosion by water vapour in warm, humid conditions forming a milky film which cannot be wiped off. That could be it. Otherwise an average glass.

 

David

It’s not the fluorite element that’s the problem.

[Terra Nova]

One last thing you might try Steve. Since it’s the flint element and not the Fluorite one, and it already is damaged so nothing to loose, try cleaning it with dilute hydrochloric acid (conc. ~15 to 30%) such as that labeled ‘muriatic acid’. What your photograph shows looks like a hard salt or carbonate deposit. HCl might do the trick and it shouldn’t harm the glass. You’ve tried a lot of organic solvents (acetone, alcohol, etc.) and they usually won’t easily dissolve inorganic compounds. If you have a salt or carbonate or Na, K, Ca, or Mg, the HCl with react with the metallic cations and dissolve the compound.

[Steve_M_M]

Off to the store I go 

[davidc135]

It’s not the fluorite element that’s the problem.

K5 and K7 are the glasses that partner fluorite in the doublet designs that I looked at, not fluorite itself. I found the glass types in 'Telescope-Optics.net' section 9.2.1.

 

+1 for the possible carbonate deposit but K7 according to my Schott catalogue is fairly, but not very resistant to the 0.5N Nitric acid that they used in their tests. 30% Hydrochloric acid is 8N so a short spell is fine but I wouldn't leave it overnight.

 

David

Edited by davidc135, 21 May 2022 - 02:07 PM.

[deSitter]

K5 and K7 are the glasses that partner fluorite in the doublet designs that I looked at, not fluorite itself. I found the glass types in 'Telescope-Optics.net' section 9.2.1.

 

+1 for the possible carbonate deposit but K7 according to my Schott catalogue is pretty but not very resistant to the 0.5N Nitric acid that they used in their tests. 30% Hydrochloric acid is 8N so a short spell is fine but I wouldn't leave it overnight.

 

David

"Carbonate deposit" - how? How do these defects happen, and what can be done to mitigate them? Is Japan just a notoriously bad environment for telescopes?

 

-drl

[deSitter]

K5 and K7 are the glasses that partner fluorite in the doublet designs that I looked at, not fluorite itself. I found the glass types in 'Telescope-Optics.net' section 9.2.1.

 

+1 for the possible carbonate deposit but K7 according to my Schott catalogue is fairly, but not very resistant to the 0.5N Nitric acid that they used in their tests. 30% Hydrochloric acid is 8N so a short spell is fine but I wouldn't leave it overnight.

 

David

Yes I was actually thinking about an acid bath for a short spell in the hope that this is some sort of oxidation that can be quickly removed. Even sulfuric acid at some strength would be harmless to hard glass.

 

-drl

[davidc135]

Interesting to see what the acid test turns up. Any carbonate should go easily but some calcium salts could be tougher. Surface corrosion by warm water vapour might leave a powdery silica (?) effect needing polishing or other mechanical method.  David

 

PS I'd measure the spacer thickness.

Edited by davidc135, 21 May 2022 - 02:51 PM.

[deSitter]

Steve, since you are in the "tried it all" phase, try this If the material is amenable to removal with acid, this will tell you. Let it sit for, say, 2 minutes followed by a long wash, then 5, then 10 etc. If you see progress, then a real sulfuric acid bath might just work. I am sure the glass will be unaffected.

 

PS if you try this, have a weak basic solution (e.g. sodium bicarbonate) to neutralize any excess acid, and of course take proper precautions with gloves and eye protection.

 

https://www.lowes.co...-Opener/3371170

 

-drl

Edited by deSitter, 21 May 2022 - 02:59 PM.

[Steve_M_M]

 

 

PS I'd measure the spacer thickness.

Funny, I lost one early on and quickly realized I had better measure the remaining one off the lens just to be sure.  I did find it, so i have the original 3.  It’s been amazing how that last spacer has held on through all of this.  

[Steve_M_M]

Well, a 10 minute, then 1 hr, then 3 hr, then overnight soaking in Muriatic acid saw no change to the lens.  Although the remaining spacer disintegrated into nothing.

 

I have seen some posts elsewhere that the issue is "in the glass".  I struggle with this concept as the missing spacers all left a nice tiny area the size of the spacer which is clear and without fog/haze.

[deSitter]

Well, a 10 minute, then 1 hr, then 3 hr, then overnight soaking in Muriatic acid saw no change to the lens.  Although the remaining spacer disintegrated into nothing.

 

I have seen some posts elsewhere that the issue is "in the glass".  I struggle with this concept as the missing spacers all left a nice tiny area the size of the spacer which is clear and without fog/haze.

Try the sulfuric. Much more effective at cleaning up salt deposits.

 

-drl

[davidc135]

Somehow the glass surface has been attacked by water vapour or condensed water, small areas being protected by the foil spacers either physically or by altering the chemistry under the spacer.

 

David

[Steve_M_M]

Try the sulfuric. Much more effective at cleaning up salt deposits.

 

-drl

That is the last try happening tonight after dinner.  I tired several other methods today, some pretty radical, with no change whatsoever.  

[Linn]

If I remember right, people have used denture cleaning tablets to clean old film developing tanks that were crusty. 

[Dave Trott]

Looks like it might be time to learn how to repolish or refigure a lens. WOW, what a challenge! 

Edited by Dave Trott, 22 May 2022 - 09:56 PM.

[davidc135]

Hopefully the sulphuric acid works but if it doesn't I'd try to see if the frostiness is on top of the glass or etched into the surface, or both and get an idea of how deep the problem is. The lens can be held up to a light bulb and the Ortho 18mm will show the finest pits. The surface can be compared with a piece of scrap glass fine ground with standard 9 micron smoothing powder.

 

David

[RichA]

Well...

 

I ALWAYS work from Least Dangerous to More Dangerous....

 

- First:  Alcohol

- Second: Vinegar (or, Peroxide for mold)

- Third:  Windex

- Fourth:  Bleach, Baby!

 

Coatings?  Who needs those?  (Actually, in practice, brief immersion in bleach hasn't hurt the flint coatings.)

 

I'm not a chemist, and I'm sure there are other readily-available chemicals to try on these "hazy flints" but I've found pure bleach to be about the strongest at cleaning it...

 

BB's Big Question:  What causes the hazing in these TAK Flints?  Traditional Crown + Flint Doublets have been around for a Long Time, yet I haven't seen this hazing on my older achromatics...

 

In both of my Old Taks, the fluorite element stays pristine, and I think both are uncoated...  Is the culprit the coating TAK used on the Flint??

 

(FYI:  I asked this question on the Takitis! thread, so we'll see if there's any kind of consensus.)

Windex is safer than "alcohol."  Alcohol can be all sorts of concoctions, with perfume in it as well.  Never EVER use bleach on a lens, unless you want an ersatz "coating" permanently on it.  I would go with these four in this order:

Windex (ammonia is neutral)

Wood alcohol, methyl hydrate

Acetone

Varsol (if dealing with a heavy grease)