The BRNO dri+Cap dehumidifying system will protect your lenses from fungus and is available for Canon and Nikon mount: the kit costs $44.99, single lens or body cap sell for $23.99 (B&H Photo / Adorama). The cap holds replaceable silica gel for absorbing the moisture that can lead to fungus or mold. The caps also minimize condensation build-up. Each silica gel changes color from orange to green when it needs to be changed. The caps will maintain the optimum relative humidity (RH) of 35% to 45%.
