Monstrum Tactical 3-12x42 AO Rifle Scope with Illuminated Mil-Dot Reticle and Offset Reversible Scope Rings Adjustable 3-12 times magnification, for targeting out to 500 yards and beyond Adjustable reticle illumination with 5 brightness levels in both red and green, allowing for better reticle visibility at night or in low light environments An adjustable objective lens  or AO - that allows for sharper focus of the target image, elimination of parallax, and range estimation A mil-dot reticle with markings that allows you to estimate range or compensate for bullet drop Aircraft grade 6061 aluminum scope body with a sealed, nitrogen-charged tube for resistance to water and fog