The dew shield is an extension of the telescope tube. The black coating of the shield also contributed to the prevention of diffused light. Furthermore, the dew shield helps to shield the lens from insects, dust and other dirty particles. In short, a dew shield is a vital accessory. Don’t let your viewing pleasure be disturbed halfway in the night by a few drops of dew! The ideal size for a dew shield is 1 to 1.5 times the objective diameter.