Tuneable optical filter

A filter structure for use in a filter, the filter comprising moveable filtering means for receiving and filtering input radiation to provide corresponding filtered output radiation, the filtering means having spatially varying filtration properties;

• actuating means for moving the filtering means relative to the input radiation for selecting a portion of the filtering means for use in filtering the input radiation and thereby tuning the filter, the actuating means including at least one actuating element operable in a first phase to flex relatively slowly in a first driving direction to engage with and maintain full frictional contact with the filtering means to thereby impart a lateral force for moving the filtering means relative to the input radiation in the first driving direction, and operable in a second phase to flex relatively more quickly in a second direction mutually opposite to the first driving direction such that frictional contact with the filtering means is lost and the filtering means remains in a displaced position;
• and the filter structure comprising an array of discrete filter regions for filtering the input radiation.