While the optics in vintage manual lenses exude desirable imaging characteristics, one of the biggest concerns using an old lens is the presence of fungus in the optics. This is especially problematic if you live in a tropical country where humidity is always high. We have found this extremely useful Youtube video by Mathieu Stern demonstrating step by step instructions on how to remove fungus quickly and easily from a vintage lens.
Typically the fungus may or may not be readily visible to the naked human vision, thus a quick way to detect the presence of fungus inside a lens is to shine a torchlight into the lens. The fungus usually appears as white spots and patches and may vary in severity affecting the area of the lens. Upon inspection, Mathieu found his Cyclops 85mm F1.5 lens from Russia was badly infected with fungus, and he proceeded to demonstrate how to disassemble and clean the lens. He began by removing the front element of the lens using a wrench. Next, he placed the glass under a running hot water from the tap and cleaned it thoroughly with dishwasher detergent. He dried the lens by pressing it against a high quality paper towel. To remove any calcareous residue, he poured some white vinegar onto the lens. Matthieu emphasized that gloves must be used before assembling the cleaned glass together.
Of course, these steps are applicable for lenses with simple construction which are easy to dismantle and put back together again. However, if you are dealing with modern digital lenses for DSLR and Mirrorless interchangeable lens cameras, we highly recommend that you invest in a reliable drybox with humidity monitor and controller designed specifically to protect your photography gear. Prevention is always better than cure.