Cleaning Fungus from Microscope Optics

[Atariwarrior]

Hello,

I recently took some microscopes out of storage after several years and discovered fibrous growths on some of the internal optics of my eyepieces.
There were also similar growths on the prisms of my microscope heads. I assume that they are some sort of fungus. They are visible under microscopic examination.

Does anyone have any tips on removing/cleaning this fungus without scratching the optics?

[PeteM]

If you search this site, you'll find some answers. Search is typically easiest if you Google something like "cleaning fungus from lenses site:microbehunter.com"

[apochronaut]

There two scenarios. One is the fungus is growing on a film or fine airborne debris deposited on the glass or two is on the coating. Since almost all optics have been coated for many years now, I assume it is on the coating. If the microscope is older you might be lucky and it is on glass only.
Sometimes the hyphae are living excluseivly off of the deposited substrate and sometimes the coating gets damaged too, probably by enzymes but it is possible that the coating gets utilized as nutrient as well. Usually fungus can be lifted off of glass but if on for a long time, even glass can be damaged by the enzymes.

The substrate will likely have a fat component, so I use a mild surfactant on each lens element separately. With eyepieces , I remove each lens element and with a tiny drop of plain clear unscented dish detergent on my index finger and thumb I very gently smear the detergent around on the two surfaces as the lens is held between my index finger and thumb for 10 or so seconds then thoroughly rinse under a fine stream of warm tap water. I follow up with isopropyl to kill any remaining spores, and then swabs or lens paper. Once dry, you will see if there are any track marks on the coating or glass. Usually not much can be done if there are residusl marks left but with eyepieces, marks on surfaces remote from the field stop can often be almost invisible. Immerse the metal parts of the eyepiece in isopropyl for about 5 minutes to kill any spores.
I wouldn't remove the prisms. Just clean them in a similar fashion but since you can't rinse them, dilute the detergent well and rinse with wet swabs, following up with isopropyl and dry swabs.Clean the surrounding parts of the head as much as possible with isopropyl soaked swabs and when everything is dry blow out the head with a blower bulb or light compressed air if possible.
Once the glass surfaces are clean and sterile, recolonization is unlikely for a long time but if you store it away again you might consider trying to ventilate it somehow. The storage area is the source of spores and could be heavily infested . Mould spores are endemic and difficult to avoid so lowering the humidity level is a good option.
I would check the other optics too.
Some people pack microscopes away in sealed containers. This is a good idea, as long as you are sure that the container is not going to provide a nice sealed environment for spores to germinate and grow in.

[Galf]

Recently I obtained a Leitz trinocular head from about 1973 but I found the rod that moves the photo-prism was stuck and the left eye prism was rather misty and had grease or fungus on it. Those heads are surprisingly easy to open up and cleaning the optics with isopropyl was sufficient. The prisms are sturdily fixed so cleaning all glass surfaces was a breeze. It is all clear now and working perfectly after connecting the rod to the correct slot on the prism-slide which sends all light to the eye-pieces or when engaged, 80% to the photo-tube and 20% to the eye-pieces.

Dissecting oculars or objectives is more a challenge for me. Not the dissecting but the correct assembly afterwards without introducing more dust than before

When I store my optics I always put a number of silica gel bags with it. Those bags can be recycled by drying them in a microwave oven after each use.

[Phill Brown]

Zeiss coated optics cleaner spray.
For when you assume the coating is damaged after isopropyl meths soapy didn't work.

[apochronaut]

Zeiss coated optics cleaner spray.
For when you assume the coating is damaged after isopropyl meths soapy didn't work.

Meade and Takahashi apparently don't trust it on their coatings. There are reports of it damaging the coating on astronomical instruments. It's target market may be eyeglasses which have a a more durable finish.
If that's the one containing 2-butoxyethanol, which is a common ethyl glycol derived industrial surfactant, used as a cleaner and paint solvent.

The principal of lens cleaning solutions is common. They are surfactants and solvents in a water base, with the idea that no residue be left. I question the logic of that latter characteristic in the case of a packaged lens cleaner, where removal of the product is dependant on it's absorption by a tissue or cloth. Additionally, a product that is prepackaged must also have a shelf life, which implies that usually some form of preservative is included in the formula, which at degradation could be utilized as a food source for fungi, as could the the breakdown products of detergents. The combined nature of packaged lens cleaners then, is almost sure to leave some form of residue behind, which could be utilized as a substrate by fungi.
Since the original poster was not asking about cleaning lenses in general but about a specific case where the environment created conditions favourable to the growth of fungi, it seems a better protocol to clean with a surfactant and sterilize with an alcohol in separate steps. One of the benefits of finishing with a pure alcohol rather than a combined alcohol/surfactant/preservative solution is that the alcohol is highly evaporative and when the procedure is done properly much less likely to leave a residue. Cleaning lenses with a lens cleaner in this case as well, can do nothing to destroy the millions of spores that would cover the non optical parts of the prism and lens housings.