The 40mm objective lens features an adjustable objective design (AO) that allows parallax correction. Hawke Sport Optics designed this rifle scope to allow you to easily reset your windage and elevation levels to zero with 1/4 MOA clicks. The Hawke Sport optics 4-12x40 Vantage AO Mil Dot Riflescope was designed for mid to long-range use thanks to the broad magnification range and excellent low-light performance. The Vantage 4-12x40 AO Riflescope (Mil Dot Duplex Reticle) brings you exceptional image quality thanks to the optically indexed 11-layer anti-reflection fully multi-coated optics. The Vantage Riflescope lenses are fully multi-coated with eleven-layer anti-reflection multi-coatings that deliver maximum light transmission and minimum glare on all air-to-glass surfaces.