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Help with Unitron Lens

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#1 stevenk

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Posted 18 February 2020 - 04:42 AM

I am hoping for some advice or Help

 

I had started a topic but hoping for a bit more guidance

 

I have a Unitron lens with what appears to be coating smears on the flint surface where the spacers are 

I don't know if it is damage or what but they are weird shapes - 

They are not chips at all or broken or cracked glass- under high magnification it does seem like a stain of some sort??

I have tried window cleaner diluted and Isopropyl but no go

 

If anyone knows how to clean I would be most grateful - Or if anyone can advise what these stains are and how these could have occurred ?????

Thanks

 

Steve

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Edited by stevenk, 18 February 2020 - 04:45 AM.


#2 beanerds

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Posted 18 February 2020 - 05:15 AM

They look like classic ' Clamb Shells ' , if you are worried about them just remove the lens's marking their orientation then removing the small ' Clam's ' and blackening the broken pieces of the main lens elements with a black Sharpie .

 

Doing that it will perform to about 95% which with one of these telescopes will and still be AWESOME ! 

 

Beanerds 


Edited by beanerds, 18 February 2020 - 05:18 AM.


#3 stevenk

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Posted 18 February 2020 - 06:06 AM

Thank you but no they are not breaks or clams chips

 

As mentioned in my post. the lens is not broken it is entirely intact - I have taken the lens apart and they are marks on the coating which I cannot remove

 

I have examined under a magnifier and they are some type of stain or coating damage - but why there near the spacers and how could this type of coating damage have occurred on the flint ?

 

Has anyone seen anything like this before ?


Edited by stevenk, 18 February 2020 - 06:18 AM.


#4 davidmcgo

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Posted 18 February 2020 - 08:22 AM

Try acetone, anything that came from the adhesive should come off with that.  If from hard water, try vinegar.

 

Dave


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#5 Chuck Hards

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Posted 18 February 2020 - 08:32 AM

Moisture can condense between the elements or on the rear surface of the flint.  Left for long periods, it can etch the glass due to pollutants in the air.   It can also damage coatings and lead to fungus growth.


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#6 ccwemyss

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Posted 18 February 2020 - 12:42 PM

I've had luck removing fungus using Scrubbing Bubbles with Bleach cleaner, followed by a thorough distilled water rinse, and sometimes isopropyl after that. There can then be areas of missing coating where the fungus was, which are visible with reflected light. But if they aren't visible when viewing through the glass, it's not going to have a significant effect on the image. 

 

This doesn't look like fungus marks. More like somebody tried cleaning it without removing the glass from the cell, using a solution that wicked between the elements around the spacers through capillary action, and then either left a residue, or dissolved the coating.

 

If you can see it distorting light while looking through the glass, then it is worth trying to get rid of it, assuming it is residue and not etched into the glass. If the glass looks transparent in transmission, then it may be fine as is. 

 

Chip W. 


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#7 starman876

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Posted 18 February 2020 - 01:26 PM

Whatever it is it most likely interacted with the coatings. Maybe the only way to remove it is by polishing it out. I have removed old coatings using rubbing compound. Some have said that lemon juice will remove old coatings. Or you could send the lens to a place that puts on new coatings and maybe they also know how to remove old coatings without polishing. Try spectrum coatings and see what they say they can do for you.
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#8 DAVIDG

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Posted 18 February 2020 - 02:08 PM

Thank you but no they are not breaks or clams chips

 

As mentioned in my post. the lens is not broken it is entirely intact - I have taken the lens apart and they are marks on the coating which I cannot remove

 

I have examined under a magnifier and they are some type of stain or coating damage - but why there near the spacers and how could this type of coating damage have occurred on the flint ?

 

Has anyone seen anything like this before ?

 As chemist what I think happened is water got in the cell. It stay there long  enough to react with the metal in the spacers. The spacers are most  likely aluminium and Aluminium Hydroxide was formed which is basic in pH. That dissolved the anti reflective coatings. Also Flint glasses contain certain rare earth elements that are used to change the refractive index. These elements can be dissolved out of the glass with acids or bases. This why more exotic glasses used to make APO are placed in the rear of the objective if it is two element system or in the middle if it a three element system to protect the glass from environmental damage.

 

        - Dave 


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#9 CHASLX200

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Posted 18 February 2020 - 07:22 PM

Best to just live with it.  No way i would take it apart.



#10 starman876

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Posted 18 February 2020 - 07:50 PM

 As chemist what I think happened is water got in the cell. It stay there long  enough to react with the metal in the spacers. The spacers are most  likely aluminium and Aluminium Hydroxide was formed which is basic in pH. That dissolved the anti reflective coatings. Also Flint glasses contain certain rare earth elements that are used to change the refractive index. These elements can be dissolved out of the glass with acids or bases. This why more exotic glasses used to make APO are placed in the rear of the objective if it is two element system or in the middle if it a three element system to protect the glass from environmental damage.

 

        - Dave 

That is a very good explanation of what most likely happened Dave.  Can it be salvaged or is something the poster has to live with?


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#11 stevenk

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Posted 18 February 2020 - 10:49 PM

I totally agree. What a great and logical explanation!!  This is what I love about this forum .I am always learning! 

And Starman  thank you for asking whether it can be salvaged.

 

Under high MAG it seems like a surface blemish, but I am worried that the coating has been stripped.  But if not can I assume aluminium hydroxide is the substance that is showing up as silvered. What can I use to wipe it off.? 

 

Thanks again. 


Edited by stevenk, 19 February 2020 - 02:20 AM.


#12 clamchip

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Posted 18 February 2020 - 10:53 PM

I would try Acetone as Dave suggested.

 

Robert


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#13 Bomber Bob

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Posted 18 February 2020 - 11:32 PM

I just cleaned a Royal Astro lens for a fellow CNer.  After unpacking it, I thought it was ruined:  1 large + 2 smaller spiders of mold / fungi between the elements that looked like they had etched the coatings if not the glass.  But, after a peroxide soak, and thorough cleaning, only 1 ~ 1mm spot + a few scattered pinpoints remained in the coatings.  (Why is it that the R3 / flint skyward face collects the most growths?  Is there something about that element's chemical composition compared to the crown?)

 

I would definitely clean this lens -- carefully.


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#14 stevenk

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Posted 19 February 2020 - 02:24 AM

Thanks guys. I will try all 

 

I would try Acetone as Dave suggested.

 

Robert

 

and report back. The collective intelligence on this forum never ceases to  amaze me. 

 

Steve 



#15 DAVIDG

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Posted 19 February 2020 - 09:59 AM

 It's not going to hurt to try Acetone but Acetone like alcohols  is an organic solvent so it is good at dissolving organic material like oils. If the stain on the lens is inorganic like a metal salt then acetone won't tough it. If it is a metal salt then you need an inorganic acid or base. The problem is that can also etch the glass. What you can try is warm to hot distilled water. It may take hour to days to dissolve the deposit, if it is on the glass. From the picture thou I think that the anti-reflective  coating has been dissolved and what your seeing is bare glass. 

 

                - Dave 



#16 Kokatha man

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Posted 19 February 2020 - 08:53 PM

...just reading this thread as people post Steve - I did alert folks here to that lens when the fella on IIS advertised it last week: hope you can sort something out! waytogo.gif

 

As far as removing the coating in areas that are affected, I'd imagine that doing so in those areas specifically might be preferable to stripping off all the coating-covering of the lens if they only represent a small portion of the lens total area & are only on the peripheries...although I seem to recall that there was only about a 2% transmission loss if the coating was completely removed. Ghost images are the major issue with un-coated optics afaik... 

 

Although I told folks here that Wayne Sainty has ceased running his business in NSW just before Xmas I spoke to him just now & he has relocated & expects to be operational by March sometime...good news for AA'ers in Oz..! smile.gif

 

When discussing your situation I should have re-read all this thread...but Wayne's take is that you could try stripping the coating (probably MgF2) with Hydrochloric acid - I suggested applying it with a fine artist's brush to very finite areas with a pail of water next to you (outside for any fumes) to constantly & frequently neutralise the acid on the lens if you wanted to try to do this only on the very finite areas where the damage occurred...

 

This might seem severe but I have done the same in conservation work in my former professional life using concentrated Nitric acid (much more aggressive than Hydrochloric btw) on fine etchings etc that were far more valuable than your Unitron lens...even hydroflouric on glass, but all in a fume cabinet - & some of this work was virtually irreplaceable..! lol.gif  

 

He can recoat the Mag. Flouride, but makes the point that if you cannot strip the existing coating off with hydrochloric acid then he wouldn't be able to either - technically HCl is not supposed to be very effective at removing these coatings but Wayne makes the point that porous coatings of said can often be removed via this acid due to their condition including porosity...

 

Polishing the coating off is then the only other option - evidenty there was a firm in Sydney that did this but no longer operates - I'd imagine in the US or elsewhere there might be facilities... confused1.gif 

 

That's about it...happy to respond further or you might like to ring him yourself - he had suggested covering the rear of the affected lens with something impervious if there was a coating on the back as well as the front of your lens if you wanted to protect the rear...I suggested etching bituminous paint which I've used frequently in etchings & bas-relief work as well as glass - it is acid-resistant & washes off easily in mineral turps...you could even try painting all the lens except to the affected areas & leaving it in a Hydrochloric bath, checking regularly - this if you are a bit gamer..! lol.gif

 

But I think the small artist's brush is by far the better approach if no other solvent/cleaner works.....on a less optimistic front, evidently the decomposition of fluorides in water yields free hydrofluoric acid - but I really shouldn't have mentioned that possibility to you in the possible stages of these "stains" occurring!

 

ps: you could just live with it btw..! lol.gif 

 

pps: do NOT use H2SO4 (Sulphuric acid) on the Mag. Flouride coatings (which would have to be concentrated H2SO4 ) as this acid produces Mag. Sulphate & Hydroflouric acid..!!! bigshock.gif step.gif

 

Further reading states Mag. Flouride is slightly soluble in dilute acids (in particular Nitric) so this might be the better approach with the artist's brush if you are so inclined...dilute HNO3 is non-fuming, but you should still do it outdoors, preferable with a fan blowing anything away from yourself! ;) 


Edited by Kokatha man, 19 February 2020 - 09:38 PM.


#17 stevenk

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Posted 20 February 2020 - 04:48 AM

Guys thank you once again - upon further investigation the coatings are definitely damaged so I will leave it as it is

as the lens performs quite well.

 

But a pity as it is Ugly frown.gif

 

Thank you again 

All my best 

 

Steve



#18 CHASLX200

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Posted 20 February 2020 - 06:36 AM

Best to leave it alone if the lens gives a good image.


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#19 starman876

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Posted 20 February 2020 - 09:00 AM

You don't see the front of the lens unless you are viewing through the wrong end.  What counts is what you see at the eyepiece. 


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#20 stevenk

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Posted 21 February 2020 - 12:27 AM

You don't see the front of the lens unless you are viewing through the wrong end.  What counts is what you see at the eyepiece. 

:-D 

 

Best to leave it alone if the lens gives a good image.

:-D 



#21 sdedalus83

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Posted 21 February 2020 - 01:24 AM

(Why is it that the R3 / flint skyward face collects the most growths?  Is there something about that element's chemical composition compared to the crown?)

It's the concave surface and is somewhat isolated from the atmosphere. It will hold more water and the water won't evaporate as quickly.




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