Potassium Dihydrogen Phosphate (KH2PO4) is a crystal noted for its non-linear optical properties. It has been used as electro-optical polarization rotators to vary the intensity and frequency doubling of Nd:YAG laser. It is hygroscopic, very fragile, lacks mechanical strength, and is sensitive to thermal shock; consequently, it must be handled with care and kept dry.

Dont you handle your camera glass with care and kept it dry ?