"....... Although there are over 100,000 fungus species, two members of the genus Aspergillus are believed responsible for most lens deterioration. Optimum growth conditions for these fungi are relatively high temperature and high humidity, but they are more adaptable to lower humidity levels than most other fungi. Fungal contamination can best be minimized by reducing the humidity of the room either by air conditioning or by installing an infrared lamp above the microscope (at a minimum distance of 150 centimeters or 5 feet). Fungi growing on glass surfaces are not attached by roots and can be wiped off, but unfortunately, residual corrosion marks remain and the original lens performance cannot be recovered and the lens must be replaced. The only effective means to avoid fungal damage to optical components is to prevent its growth in the first place."
