willie_901
Veteran
My M Monochrom was delivered in Dec 2012, showed the first spot of corrosion just short of 5 years- was replaced for free. There is a huge disparity in the amount of time that corrosion shows up- must be environmental?
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The IR filter film is chemically unstable in the presence of water. This is the root cause of the corrosion.
While average humidity varies significantly among climates, water vapor is ubiquitous in our atmosphere. So climate variations are relevant. Even if a camera is stored in a near zero humidity environment, when it's making photographs water vapor in the atmosphere will react with the IR filter layer film. For this reason - sooner or later - every original sensor will corrode.
Another variable is sensor cleaning. Wet cleaning solvents can contain water. For example, isopropyl alcohol is hydroscopic. Sensor cleaning can cause very shallow scratches that have no optical consequences. But these disruptions in the cover-glass surface increase the rate of water vapor penetration. So even dry cleaning methods can affect the corrosion rate.
Yet another variable is the photographer. Corrosion artifacts are most obvious with narrow lens apertures. Those who rarely use narrow apertures will not notice obvious artifacts until the corrosion regions become large. Those who never view highly cropped images will not notice obvious artifacts until the corrosion regions become large.