Minolta MD Tele Rokkor 135/3.5 (II): Fungus removal and cleaning

[Andreas Thaler]

The next project to be brought to the table is this MD 135/3.5, which is infested with fungus and is otherwise in mint condition.

It remains to be seen whether there are any permanent chemical burns on the optics.

Get rid of the fungus!

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In the third photo, the white spots on the back of the lens are not fungus.

Rather, it is Schneideritis, a sign of aging in the material that seems to be typical also for this lens.


My plan:

• Removal of all lenses
• Remove the fungus residue with lens paper soaked in hydrogen peroxide 3 % solution.
• Dry
• Clean with surgical spirit
• Cleaning the holders for the lenses in the tube, also with hydrogen peroxide and surgical spirit.
• Assembly

If there are already chemical burns on the lens surface caused by the fungus, I could try polishing it with cigarette ash.

Maybe our neighbor will give me some

The front two lenses are held by the decorative ring and lie on top of each other in the tube, separated by a ring.

There are obviously two more lenses underneath (it should be a five-lens lens, three lenses are removed), the attachment of which I understand to be an element screwed into the tube.

There are no starting points for the adjusting wrench, unscrewing it with the rubber cylinders didn't work.

The fungus is located on the back of the lower lens.

And I can reach it through the open aperture.

The fungus cannot be scraped off; careful probing with a toothpick and screwdriver results in compact structures.

I hope the glass isn't etched yet.

And I also hope that there is no coating between the two lenses.

Well, I don't have to disassemble everything. The main thing is that I can kill the fungus.

The fungus is also on the rear lens which I was able to dismount.

So that the aperture blades are not held under tension, I unhook the relevant spring.

Then I fix the aperture lever with adhesive tape.

So when working on the lens through the aperture opening, the aperture blades are protected from a snapping "aperture trap" that could bend them.

After blowing dust off the surface of the lens (yellow circle), hydrogen peroxide 3 % acts on the fungus. I applied it with a soaked cotton swab.

During the exposure time of about five minutes, I move the stick in a spiral shape over the lens at intervals.

At the same time, cleaning work on the tube with foam swabs in isopropyl alcohol.

I don't know whether this is greenish old grease or glue, but it has no apparent function here.

So get rid of it.

The fungus dissolved without resistance as a result of the treatment.

Reworking with surgical spirit and cotton swabs results in a clear lens.

It's not that easy with the spirit, as a fine streak always remains here and there.

Patience and a foam swab moistened with a little spirit can help here.

There are also no visible signs of chemical burns caused by the fungus

Now to the rear lens, which is not only dusty but also infested with fungus.

Hydrogen peroxide ...

 

[Andreas Thaler]

... surgical spirit ...

... the lens is clean.

Cleaning the aperture ring ...

... and the bayonet with isopropyl alcohol.

I also clean the two front lenses with surgical spirit on lens cleaning paper.


Assembly

Attach the spring for the aperture.

Screwing in the rear lens.

Tighten with the spanner wrench.

The aperture ball catch cleaned with isopropyl alcohol receives some grease.

The MD 135/3.5 has been cleared of fungus and is ready for use

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Conclusion

• The fungus gave way surprisingly quickly and without resistance. The hydrogen peroxide dissolved it almost instantly. There was no permanent clouding caused by chemical burns.
• Cleaning with surgical spirit is not that easy. On the one hand, it removes greasy things very well, but occasional fine streaks can remain. Reworking with a cotton swab moistened in little surgical spirit helps.
• When checking with the LED lamp, even the finest cleaning marks (streaks) can be seen, but these are not visible in bright, diffuse light. There was also some dust. I might have been able to remove these fine streaks with the lens cleaning cloth, but I want to work as little as possible on the inner lenses because their coating may not be as robust as that of the outer lenses. Instead of continuing to clean here, I accept the fact that I'm not working in the clean room. In any case, I have to look very closely in the LED light to find these irregularities. In some cases the dust reflects the light more strongly. Completely unimportant in practice and only gets attention here because it is an issue.
• Good news for everyone who fears the fungus: it can be finished off. And it doesn't jump on the table when opening a lens
• Yes, I would buy a lens that was offered cheaply with the "Fungus" label on it again at any time. At least if the infestation is within the scope seen here.

 

[Andreas Thaler]

Addendum

Of course I opened the lens again to remove the last mini streaks.

It worked quite well with isopropyl alcohol, so I first applied it generously with a cotton swab, blew it off a little and then wiped it off with a dry swab.

This worked for the lens in the tube that I worked through the aperture.

Unfortunately not for the first one from the beginning as the cotton swab made scratches on the underside.

So far, all the lenses that I have cleaned in lenses have been robust, and no scratches occurred during cleaning. This one was soft on the bottom.

Since then, every lens in an objective that I clean, I carefully check it with the pointed probe to see if it is scratch-resistant.


Final conclusion

• You can't be too careful.
• Hydrogen peroxide 3 % is a fungus killer.
• Isopropyl alcohol is probably the less streak-free solvent on optical glass. Zeiss lens cleaning solution does also an excellent job there.
• Cotton swabs for main cleaning only highly controlled where it cannot be avoided due to the conditions. Dry or minimally moistened for spot cleaning.
• Lens cleaning paper always wet.

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All information provided without guarantee and use at your own risk.

 

[Bearman]

Congratulations on defeating the pesky fungus.
You mentioned using 'surgical spirits'. Online I found different formulas. Does the spirit you use include Methyl Salicylate 0.5%?

 

[Andreas Thaler]

Thank you

It should be benzine or white spirit, a particularly pure form for medical use that is available in pharmacies in Austria. But Zippo or another lighter fluid will probably work just as well.