Fungus means an Infestation of optical instruments with fungus spores which germinate and produce more spores.
Lens surfaces are irreparably damaged by metabolic products of the fungus (e.g. acids). Its damage ranges from cloudiness to opacity caused by the film. The Carl Zeiss T* coating has no significant influence on fungus growth or generation of spores.
Where does fungus come from?
Fungus spores are everywhere and germinate under suitable environmental conditions:
How can fungus be avoided?
Reduce the relative humidity to less than 60% (never under 30% as it is dangerous for the instrument) by storing:
After the work is done, Immediately clean the instruments. If possible, you can use a fan to facilitate evaporation of surface moisture. Do not use containers made of leather, textiles or wood for storage. Short solar radiation or irradiation with UV light may also help avoiding fungus.
How can fungus be removed?
Note: In general, Carl Zeiss does not accept instruments infested by fungus.
Clean affected surfaces with a cotton wiper that has been soaked with a disinfectant. You can build your cotton wiper, using cotton wrapped around a toothpickin such a way that a ball with a peak forms on the pointy end of the stick. Use pure cotton, no prepared or impregnated cotton. Strongly rub slightly corroded optical surfaces with an optical cleaning cloth, cigarette ash can be used as a polishing aid. Heavily corroded optical surfaces must be replaced. Fungus infestation in the interior of an instrument can only be eliminated through disassembly of the instrument.