The common defects in optical microscopes, belonging to the optical part of the lens are: mold, fog, glue, surface coating damage or peeling off.

Belongs to the mechanical part has: parts deformation, grease dry, dirty and parts rust caused by the movement of difficulties and due to wear and tear (mainly coarse adjusting guide rail and rack and pinion) and generated loose.

Examples of correction include image deterioration caused by changes in the position of each optical lens (mainly the objective lens) and image tilt and optical axis non-parallelism in the case of binocular polarizing microscope.

An optical part of an optical microscope is moldy when it shows spider-like material on the optical part. Mildew is caused by mold reproduction. Mould is a kind of microorganism, there are aspergillus, penicillium, followed by Mucor, Rhizopus and incomplete bacteria. For mold to propagate, it must have the following four conditions:

1) Mold seeds, called spores. Without spores, there is no way to grow mycelium and mildew ear.

2) temperature. The suitable temperature for bacterial growth and reproduction is 25-35℃. Below 12℃, it stops growing, above 40℃, it is close to death. As for spores, it takes 110 degrees Celsius to kill them.

3) humidity. The optimum relative humidity for the growth and propagation of notheliomycetes is 80-95%. When the relative humidity is lower than 60%, all the notheliomycetes, except a few, will grow compact-tolerant.

4) Nutrients. Molds are "saprophytic" microorganisms that will not grow without food. The main nutrients of haze bacteria in the instrument are grease, perspiration, old skin layer, dust in the air, residual impurities on the metal parts near the lens, and fingerprints left by careless finger touching the optical lens, etc. The carcass of mites (a kind of invisible microorganism) is a good food for mold to entangle, it forms the core of mold growth.

The growth and reproduction of mold must meet these four conditions at the same time. As long as one of the conditions is destroyed, it cannot grow and reproduce.