Vector Optics Frenzy-S 1x17x21 GenIIThis red dot uses the Shield RMSc footprint standard. 3MOA Strikes a Balance Between Fast Target Acquisition and PrecisionAspheric Lens Minimize the Aberration & Free of Image DistortionBattery Side Loading, Can be Easily Replaced and Won't Lose ZeroMotion Sensor Feature, No Worry to Forget to Switch Off the SightMade From 7075 T6 Aluminum Alloy As Strong As Steel Hardness Magnification N A Window Lens Size Objective Lens Size 17x21 mm 0. 67x0. 83 in