The Celestron Dew Shield DX is an essential accessory that protects your optical tube in the field. It prevents excess moisture in the air from forming condensation on the corrector lens. A dew shield also helps block stray light from entering the telescope for better viewing and astroimaging. Use the Dew Shield DX on your 9.25 inch and 11 inch Schmidt Cassegrain, EdgeHD and RASA (with single dovetail) optical tubes with confidence. It is built from durable PE plastic that is flexible but strong. Extra padding has been added at the tube attachment edge to create a stronger fit on the optical tube. The felt-lined interior absorbs any additional stray light and excessive moisture, creating optimal contrast when viewing and imaging. The large dovetail cutout has been made both wider to accommodate a 4 inch wide dovetail rails, as well as deeper, to create a more solid connection with the optical tube.