Vortex Optics Viper PST Second Focal Plane Riflescopes Optically indexed lenses deliver optimum image sharpness/brightness with true reticle use. Extra-low dispersion (XD) glass increases resolution & color fidelity for crisp, sharp images. Proprietary XR fully multi-coated lens coatings increase light transmission for maximum brightness. 30 mm tube provides greater strength and wider adjustment latitude than a 1" tube. One piece aircraft-grade aluminum tube delivers strength & rigidity for improved accuracy, optimum visual performace, durability & waterproofness. O-ring seals prevent moisture, dust and debris - results in waterproof performance. Filled with argon gas to inhibit internal fogging. TMCQ MOA reticle (Tactical Milling Close Quarter) hashmarked ranging reticle, glass-etched for optimum durability & reliability. Illuminated reticle & illumination control. MAG-view bar for clear viewing in low light conditions.