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How do I remove mold / cement failure from a vintage finder lens?

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#1 Bob A (SD)

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Posted 04 February 2021 - 11:48 AM

I have a vintage University 8x50 right angle correct image finder that has developed mold on the objective lens.  I'm not sure if the mold is on either of the exterior surfaces or if inside the objective doublet.  undecided.gif

 

What do I do to best remove the offending growth?

 

Appreciate any counsel, advice, and wisdom!  lol.gif

 

EDITED:  based on the comments about cement failure I've modified the thread subject line.  bow.gif

 

 

 

Here are some pictures:

 

Y0cvdAP.jpg

jEAI5fZ.jpg

01EBKUI.jpg

 

This picture simply shows the retaining ring cut outs for removal.  I don't have the special tool needed and know that any attempt with a screwdriver in my 73 year hands will be a recipe for disaster.

QBIktxS.jpg


Edited by Bob A (SD), 04 February 2021 - 01:05 PM.

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#2 pyrasanth

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Posted 04 February 2021 - 11:55 AM

I would use this https://www.photoniccleaning.com/

 

However mold can eat into the coating and glass so possibly expect some peppering of the surface. After that it is then a case of addressing the conditions of storage which has allowed the initial mold growth. I'm not sure about solutions that can prevent regrowth on delicate optical surfaces- that would be another area of research.

 

More info that may help https://photo.stacke...o-get-rid-of-it


Edited by pyrasanth, 04 February 2021 - 12:06 PM.


#3 ngc7319_20

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Posted 04 February 2021 - 12:04 PM

Just clean it like you would any other lens.  Use some rubbing alcohol (91% preferred) on a KimWipe / Q-Tip / etc to kill the stuff.  Avoid pressure in case coatings are damaged.

 

This might be in the cement between the two elements.  That will be tougher.  In that case, use a spanner to get the glass out.  Soak it in strong solvent like Acetone or Lacquer Thinner to loosen the two elements.  Might need to soak it for days.    Use a metal or glass container.  Wear nitrile gloves.  Work in garage or outside.  Once the elements separate, clean them off.  You can temporarily re-cement with mineral oil.


Edited by ngc7319_20, 04 February 2021 - 12:10 PM.

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#4 markb

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Posted 04 February 2021 - 12:33 PM

Back up a bit.

 

The 'snowflakes' are characteristic of canada balsam cement failure. Fungal infestations are characteristic 'hairy' growths, usually from a distinct pinpoint.

 

I've single single large snowflakes, I assume the tiny finder failed in multiple spots.

 

There was an extended thread, mainly with DavidG leading, about separating and recemeting binocular lenses.

 

Larger lenses will require heat.

 

+1 on ngc7913_20 suggestion of separating, cleaning and temporarily reassembling with mineral oil. Optical gel is sold for this purpose, too. But mineral oil is fine.

 

I've redone several doublets this way, most notably my Dad's 1951 Steinheil 6x30.

 

I used that classic, 3 in 1 oil. Light sewing machine oil should be fine, I have found Hoppe's gun oil to be particularly helpful in other situations and would use that too.

 

The first repair lasted 10 years. The Steinheil lens cell was nicely machined, finely enough to maintain element centering. I'll get another 10 years, I expect.

 

Incidentally, the Steinheils are up there with my Leitz and Zeiss classics.

 

The right way as in the bino thread, is to clean and reassemble with Norland UV optical cement.

 

I'll have to go this way on a pair of flak bino10x80s.


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#5 Garyth64

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Posted 04 February 2021 - 12:35 PM

I agree with Mark.  I believe it is the cement between the lenses.


Edited by Garyth64, 04 February 2021 - 12:36 PM.


#6 markb

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Posted 04 February 2021 - 12:42 PM

If you do have any fungus, I've used an old photo tip, Ponds Cold Cream in the past. I assume it breaks down the cellular structure.

 

On bino prism and camera lens elements, I've used an initial household hydrogen peroxide spray and wipe, followed by propanol Zeiss wipes, and occasionally acetone. Acetone is recommended for general cleaning by several experts, but I find it streaks since it evaporates too rapidly, so it is an intermediate step for me, not final.

 

I have not had glass etching, but coating etching can happen.

 

But, not expected to be your issue here.


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#7 Berny

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Posted 04 February 2021 - 12:47 PM

When I look at the first picture carefully, it becomes obvious that whatever it is, is not happening on the front surface. 



#8 Jon Isaacs

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Posted 04 February 2021 - 12:48 PM

Bob:

 

I agree with the others, it's the cement unbonding.

 

The one thing I can add:

 

For a spanner: I use a pair Harbor Freight 6 inch digital calipers that have died.  They're about $20 and last a few years. They're tough, high quality steel, with long blades, both inside and outside.  You could probably use one that's working but since I have one that doesn't, I use it.

 

https://www.harborfr...iper-63711.html

 

Jon


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#9 Bob A (SD)

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Posted 04 February 2021 - 01:19 PM

What other substances besides acetone can safely be used to separate the doublet elements?  undecided.gif

 

I have acetone here but concur with comments about it streaking quickly especially in my neck of the woods with very low humidity.

 

Lacquer thinner was mentioned... anything else?

 

 

 

For reassembly, 3-in-1 and mineral oil are on hand here too.  waytogo.gif

 

 

Jon,  great suggestion about calipers.  I'll have to check but I think I have a non-functional digital set here too.  bow.gif


Edited by Bob A (SD), 04 February 2021 - 01:27 PM.


#10 j.gardavsky

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Posted 04 February 2021 - 01:34 PM

What other substances besides acetone can safely be used to separate the doublet elements?  undecided.gif

 

I have acetone here but concur with comments about it streaking quickly especially in my neck of the woods with very low humidity.

 

Lacquer thinner was mentioned... anything else?

 

 

 

For reassembly, 3-in-1 and mineral oil are on hand here too.  waytogo.gif

 

 

Jon,  great suggestion about calipers.  I'll have to check but I think I have a non-functional digital set here too.  bow.gif

Bob,

 

you can use the infrared light of an old light bulb to get the Canada balzam bond fluid,

http://forum.mflense...sam-t34467.html

 

In some cases it may be enough to cure the old Canada balzam bond with the infrared light, instead of removing the old bond, getting the lenses cleaned, and cementing the doublet anew.

 

Best,

JG


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#11 ngc7319_20

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Posted 04 February 2021 - 01:36 PM

What other substances besides acetone can safely be used to separate the doublet elements?  undecided.gif

 

I have acetone here but concur with comments about it streaking quickly especially in my neck of the woods with very low humidity.

 

Lacquer thinner was mentioned... anything else?

The acetone / lacquer thinner is just to get the elements apart.  After that you will need to thoroughly clean them with rubbing alcohol, favorite lens cleaner, etc. 

 

I will admit I have never separated one this large (50mm).  Check other peoples advice on that step.  I've only done up to 3/4" eyepiece lenses.

 

Norland cement is $$$ for one-off repairs.  Mineral oil is cheap.


Edited by ngc7319_20, 04 February 2021 - 01:43 PM.

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#12 John Fitzgerald

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Posted 04 February 2021 - 01:47 PM

I agree with Mark.  I believe it is the cement between the lenses.

Agree.  It's cement failure.  Remove lens, soak in acetone, clean and dry, then re-cement.  Or, try reheating the old balsam, as above in post #10, which is what I would try first.



#13 Garyth64

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Posted 04 February 2021 - 02:03 PM

I separated a 50mm bino lens by slowly heating it up as described in the post.  It worked very well.


Edited by Garyth64, 04 February 2021 - 02:04 PM.


#14 markb

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Posted 04 February 2021 - 04:17 PM

This should be the separation and regluing link/thread. 

 

https://www.cloudyni...norland cement

 

I still would use the light machine oil alternative to UV cement, but I just dread having cement set up and then realizing I made an error. UV cement is tricky to split, even before fully set.

 

 

The easiest mistake is to flip an element, way easier to do than it sounds. I always mark the original 'spin' with a line across both with a pencil, and using 2 lines to mark an 'arrowhead' pointing to the sky helps too.

 

I have lightly etched edges if the pencil marks were expected to be covered as in blackening.

 

So far I think I bought 3 refractors/cells with a flipped element or a flipped entire cell. And I've lost track a time or two and had to refer to markings to be sore.


Edited by markb, 04 February 2021 - 04:20 PM.

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#15 markb

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Posted 04 February 2021 - 04:28 PM

If you choose to edge blacken also, don't use Sharpie, I've have odd long term results and it is not overly effective.

 

I use Higgins Black Magic india ink in marker or brush-markers from Amazon. 20 bino prisms and an f8 ⁶" Jaegers worked beautifully.

 

Flat Tamiya hobby paints are really good too, but I fear cleaning off errors and adding thickness to lens edges resulting in fitment issues. It worked amazingly well on blackening big lens lens edge clamshells, killing internal reflections.


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#16 Bob A (SD)

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Posted 05 February 2021 - 10:34 AM

JG,

 

   Brought the objective lens assembly in its housing in this morning to come to room temperature as the garage was below 20°F.   Will try the old light bulb trick later today.  Fingers crossed! 


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#17 j.gardavsky

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Posted 05 February 2021 - 11:37 AM

Bob,

 

follow the routine according to the link I have posted,

and let us know,

JG



#18 Bob A (SD)

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Posted 05 February 2021 - 12:11 PM

Bob,

 

follow the routine according to the link I have posted,

and let us know,

JG

JG,

 

  I'm taking your comments here to heart for my first attack on the problem.

 

"In some cases it may be enough to cure the old Canada balzam bond with the infrared light, instead of removing the old bond, getting the lenses cleaned, and cementing the doublet anew."


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#19 Bob A (SD)

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Posted 05 February 2021 - 01:46 PM

Well sadly that didn't work at all, so disassembly, cleaning, and mineral oil are in my future.  bawling.gif


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#20 Garyth64

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Posted 05 February 2021 - 02:34 PM

I separated a 50mm bino lens by slowly heating it up as described in the post.  It worked very well.

Hope you didn't think I was referring to the light bulb thing.  In fact I missed that post.

 

The post I that I was referring to was David G's post,  mentioned in post #4 and #14.

 

Here is another thread:

 

https://www.cloudyni...m#entry10193185


Edited by Garyth64, 05 February 2021 - 02:46 PM.

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#21 j.gardavsky

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Posted 05 February 2021 - 02:38 PM

Well sadly that didn't work at all, so disassembly, cleaning, and mineral oil are in my future.  bawling.gif

It's a pitty,

and now, it will take much more time,

JG



#22 D_talley

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Posted 05 February 2021 - 02:45 PM

This is the lens on the finder when I refurbished my Cave scope. I thought it was mold and a crack but only was a breakdown of the cement bond. 

 

After trying several things to separate the lenses, I set it in the oven at 350 F and after a few minutes  the two slid apart.  

 

I cleaned up the two with Carb Cleaner and used UV glue to put them back together.   No problem. 

 

Forgot to post the after photo.  

Attached Thumbnails

  • crackedfinder1.jpg
  • finderlensplit.jpg
  • Finder_clean.jpg

Edited by D_talley, 05 February 2021 - 05:54 PM.

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#23 ngc7319_20

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Posted 05 February 2021 - 03:55 PM

This is the lens on the finder when I refurbished my Cave scope. I thought it was mold and a crack but only was a breakdown of the cement bond. 

 

After trying several things to separate the lenses, I set it in the oven at 350 F and after a few minutes  the two slid apart.  

 

I cleaned up the two and used UV glue to put them back together.   No problem. 

Do we get an "after" photo?  :)


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#24 Bob A (SD)

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Posted 05 February 2021 - 04:58 PM

It's a pitty,

and now, it will take much more time,

JG

Concur.  :(    

 

Also tried the old caliper trick to free the lenses.  Didn't work in my old hands.  There may be a spanner available locally... we'll see.

 

WqVM1II.jpg


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#25 markb

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Posted 05 February 2021 - 05:22 PM

Oops, forgot to warn you (and others) not to try the caliper 'trick'.

 

Decent calipers have hardened tips that can easily scratch glass. Having pointed tips with beveled edges makes it a bit scarier for me, too, as the tips can pop out easily. Screwdrivers are also deadly to lens due to sharp, hardened tips. Tempting though, resist.

 

Even proper lens spanners can pop out of notches, even for long-tim tool users.

 

A plactic caliper can be used to 'run off' a loosened ring, though. I use thinned toothpicks or chopsticks, but wood can scratch coatings, too.

 

I bought a lens spanner years ago on eBay and still use it frequently.

 

Amazon has several choices in the $15-30 range.

 

The parallel arm types are the ones that pop up in searches, and they have advantages over single bar types.

 

If you want to try locally, a sometimes acceptable cheat is a snap ring tool from a good autoparts store. I have a KD AC snap ring tool that has a screw regulated opening. It gets extra throat if the screw end retainer is removed, but it loses the fixed width tips.

 

These, and other snap ring tools, take ibexpensive replaceable tips, which you can modify. While not sharp and hardened, they are hardened so care is required.




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