lens cleaning

[Berndt]

I cleaned quite a few lenses in my life, but became desperate with this one

I successfully disassembled a Petri 135 mm f:2.8 lens. All lens elements have been clean ( or possible to clean ) except one in the middle. This lens element seems to be composed of actually two further lens elements, glued (?) together.

The A side ( regarding to the attached pictures, on which I tried to photograph this issue ) seems to be contaminated, but I can't exactly tell, if from both sides, but from the outer side for sure. The B side does not seem to be affected.

Here the A side on top:


dirty lens side A by bokuwanihongasuki, on Flickr

And the B side:


dirty lens side B by bokuwanihongasuki, on Flickr


dirty lens side B by bokuwanihongasuki, on Flickr

It's pretty annoying and I would be happy, if I could get rid of it It doesn't seem to be mold for me ... it looks more like if the coating would have been partly destroyed ? Hard to take perfect pictures of it, but you can judge it best from the A side ( first picture ), I guess. Looks like a thin "oil film" ( what it is not of course ) having rainbow colors on the surface but looking like white blotches if looking through the lens ( B side pictures )

I started my cleaning from the softest tool ( just water and soap ) over alcohol ( what usually works fine ), ending up at a pretty strong thinner ... and nothing changed

Any good advices ? Would be cool, if I could rescue that lens, because those Petri mount telephoto lenses are rare to find ( especially the old ones, fitting on the V6 ).

Berndt

[mickeyobe]

This one definitely calls for the expertise of Stephen.

Mickey

[Deleted]

I'm betting fungus

[Berndt]

I'm betting fungus

Mmmmh ... but fungus is usually looking more like a fine web or tree, spreading in form of tiny branches. This one looks more streaky and blotchy.

[mickeyobe]

Have you tried vinegar?

Mickey

[Stephen]

I would say it was fungus or mould attack, it needs a microscope to see the surface to assess what has happened.

It could be re-polished, but this is not easy, you will have to obtain the fine cerium oxide in various finishing grades. It is best left to professional lens repairers, but is expensive work. Re-coating can be done, but only a handful of companies do it. Such surface repair grinding can be done by hand, the amounts of glass removed are minuscule, and do not affect the formula of the lens, unless wildly overdone.

Fungus attack is not just on the surface, the fungus generates acid that dissolves glass and digs in permanent marks within the surfaces. This is sometimes very deep in terms of microns, and difficult to remove

If it is just the coating, then it can be removed with fine grade metal polish, which is not abrasive enough to attack the glass, but this is a last resort, and non reversible, the only rescue is re-polishing with a cutting abrasive like cerium that is able to abraid glass.

Glass varies in hardness, some is quite soft to abrasives, and also glass ages, altering over time, and can soften.

Stephen.

[Berndt]

Thanks everybody. Vinegar doesn't work ... and I tried some even more serious stuff from my wife's "cleaning goods" ;D Don't ask me, what is written on those bottles, but it already smells like a whole chemistry lab.

Fungus is organic matter ... so it should become killed by one of those stinking acids ( as I remember from chemistry at school, only hydrofluoric acid - HF ) would also kill the glass itself. But ...

the fungus generates acid that dissolves glass and digs in permanent marks within the surfaces. This is sometimes very deep in terms of microns, and difficult to remove

... that might be the case as well The good news are ( if these are good news ), the infected glass surface is plain. Stephen, when you are talking about polish, would it be possible to polish the glass surface without scratching it or making it opaque ? I don't fear the removal of the coating as it is just one surface of one lens element impaired. It wouldn't be worth, taking this lens to a professional cleaning service. I need to try it by myself

[mickeyobe]

Fungus is organic. So is the mould that occurs in damp environments.

My shower stall is a damp environment.
I can keep it completely free of mould with a periodic spray of chlorine bleach.

Would it work on a lens?

Mickey

[Stephen]

There are several solutions that kill Fungus, but the problem is the hydrofluoric acid acid left by the fungus which dissolves glass, and leaves a permanent etch up to 20/ 40 microns deep, which has to be polished out.
Now this is not, repeat not, cloth polishing, It is done on a charged lap, a softer material which rotates above the glass surface, with the compound between the glass and the lap.
It can be a pitch lap, wood, or iron to an exact radius to match the lens or a pitch moulded lap made to the glass form.
Another method is a ring lap, rotating at an angle to the centre line of the lens, with the hole in the centre charged with compound, as the lens itself is rotated.
The lap does not touch the glass, it runs on the compound in the gap, the compound is rough and slowly grinds the high points away.
This process is very slow, it could take many hours to re-polish a surface, and it may need a course grade to start, and fine rouge compound to finish.
This is far more complex than can be done at home, it needs expertise and machinery.
It would be possible to remove coating by use of a leather, charged with the cerium or rouge compound, it will not re-grind enough to affect the curvature or formulae. But more than a light clean will be impossible it would take hours and not be accurate enough to maintain the curve without a proper swinging lap.
I worked for a lens maker, but did not do re-grinding, just setting up initial grinding and finishing.

Stephen.

[daveh]

Here's Ron Herron's answer: herron.50megs.com/fungus.htm

Hydrofluoric acid is pretty nasty stuff: use with extreme caution. Much kinder to the user are the anti-fungal skin treatments like Daktarin (miconazole) If it doesn't work on your lens you can, at least, get rid of your athlete's foot.

Might it not be, at least in part, the glue holding the elements together where the problem lies?

[Stephen]

Hang on, nobody said use Hydrofluoric acid, it is there naturally after the fungus grows on the glass, it is not added or used for cleaning in anyway. The acid if there long enough eats into the surfaces, leaving a permanent mark.

The use of hydrogen peroxide and ammonia as a cleaner will certainly work, but it will not remove the damage, only stop the fungus from spreading, and remove it. but it may leave the etched traces.

Slight marks like a pattern of branches etc., will not show on the neg, it will reduce contrast, which can be restored somewhat with a hood, or filters in B/W.
Stephen.

[daveh]

Stephen, Berndt said: "Fungus is organic matter ... so it should become killed by one of those stinking acids ( as I remember from chemistry at school, only hydrofluoric acid - HF ) would also kill the glass itself."

I'm not sure you can get hold of Hydrofluoric acid anyway - either literally or metaphorically.

[Stephen]

Leica used the peroxide and ammonia mixed with distilled water for lens cleaning, it is a safe and sound mixture, given care, no skin contact or splashes in eyes etc., the concentrated ammonia fumes, so do not sniff!

Hydrofluoric acid is very, very nasty, it's main use with glass is etching art glass. It is not safe to handle at home. Traces are left by the fungus on the lens, that is removed by the Ammonia, the Peroxide acts as surfactant to lift dirt and dissolve the remains of the organic fungus. Both chemicals are reasonably safe at home.
Stephen.

[Berndt]

Thanks everybody for the good ideas and recipes. I tried them all ... but ... I think, I have to give up on this one. The fungus probably destroyed the glass already Nothing seems to help.

The only thing I can do is, keeping the parts and hope to find another lens of this, where I might be able to use the clean elements for good. It's very difficult to get old telephoto- or zoom lenses in good condition here in Japan. It's the climate, the rainy seasons and wet summers. People do have better air-conditions nowadays, but many lenses became destroyed over the decades, when that hasn't been the case yet. Plus the fact, that Petri used an own lens mount. They changed that to M42 later, but I was actually curious, how the original lenses work. It's also not, that those original Petri mount lenses are expensive ... just difficult to find ... especially the zoom and telephoto ones in still usable condition.

[Stephen]

Is the surface that's damaged flat? it looks close, check by reflection, a flat can be re-polished far easier, cerium oxide to grind, and rouge to finish, telescope makers use hand methods like this.

The moisture is the problem behind fungus, it can get into some areas and remain, the front and rear elements often survive as moisture evaporates away, leaving them dry.

Moisture can also break up the glue, Canada balsam or substitute, these break with careful heating, and can be re-glued, but the glued pair require re-collimation, setting the optical centre line, far above home repairs.

Long term storage in leather is also an issue, it can encourage fungus growth, the leather stores moisture.

Store lenses in sealed containers with desiccants, dried out every so often. A good temporary travel idea is storage in the cases, with cling film over the lens, with a desiccant pack inside the cling film, as well as in the case.

A home made desiccant is rice, sewn in linen bag, and then dried in the oven, or microwave(with care!).

The rule, no moisture, no fungus will grow.

Stephen.