Originally posted by Alex645 t seems as if the metallic film used on the glass is not fused entirely and there is enough of a gap that creates the Newton's rings.
There was a similar post ages ago where there was a similar problem with newton rings and a UV filter with the DA 18-55. But in this case film separation can also be a cause, a similar thing can occur with de-laminated Polarisers. The Lee ND10 filters I work with are tinted glass, they don't use a film coating so there is no problem with separation.They Hoya filter seems to take the cheaper approach, disappointing.