This all acrylic dew shield protects the sight window from dewing. It's extra length gives many hours of trouble free use. If the dew shield dews over, just raise the window for aiming and then replace for all night protection. Raise the sight glass of the Telrad for more comfortable viewing on some scopes. Telrad risers are available in 2" and 4" height. The normal Telrad line of sight is 4.25" above the tube, the 2" riser increases that to 6.5" and the 4" riser increases that to 8.5" above the tube.