Leonard Shepherd wrote:
If it is a pol - go easy with water. Dry it first and rocket blower or use a soft brush to remove sand.
Pols are a material sandwiched between two pieces of glass. The edges are not edge sealed unless you pay extra for the few Kasemann type that remain on sale. Soaking most pols over time in water may not be a wise move-- hide signature --
Many problems turn out to be a lack of intimate knowledge of complex modern camera equipment.
Thank you, Leonard. I did not know that.