Improvement of birefringent filters. 3: effect of errors on wide field elements.

The properties of nontunable and tunable Lyot wide field elements are examined when the components of the elements deviate from their proper values. Special emphasis is put on determining what variations cause light to be transmitted at the transmission minima. The analysis shows that the nine- and ten-element plastic waveplates described in Paper 2 of this series can be used to make a Lyot filter that is tunable from 3500 A to 10,000 A.