The Primary Arms Long Relief 3X Magnifier (Gen IV) is waterproof and fog resistant. Place the magnifier behind your red dot or holographic reflex sight to instantly magnify the sight picture at 3x power. The new Gen IV model has a longer eye relief, wider field of view and improved clarity to provide an enhanced user experience. The integrated diopter provides a fast focus ability to keep the image clear. Azimuth and elevation adjustments keep the dot centered in your field of view. A rubber armor sleeve protects the body of the optic from harsh impacts.