While this tip may not be the most important for photographers who own newer lenses, it’s very important for photographers who may acquire vintage or used glass. Something that can be quite annoying is fungus. In most cases, lens fungus doesn’t affect the image quality of a photo unless the fungus severe. It also depends on the type of fungus and how much there is. The severity will also determine how you go about dealing with it.
In many cases, lens fungus can be dealt with using vinegar–specifically white vinegar. White vinegar is a gentle cleanser that can take care of this issue if you catch it early. If the lens you’re working with is a bit more infested with fungus, then it’s going to be a much different story. You’ll probably need to bring that in to an expert who will deal with it themselves.