Alpen Optics APEX Rifle Scope (4-16x44) Side focus parallax adjustments provide fast easy focus for accurate shots BDC (bullet drop compensator) glass etched reticle Spring Saddle erector tube design ensures point of aim accuracy and repeatability Fully Multi-coated optics deliver maximum light transmission and optical clarity Fully waterproof and fogproof construction with o-ring seals and nitrogen filled body.