Look through the riflescope at a blank white wall or up at the sky. Elevation Adjustment Knob Illumination and Parallax Focus Knobs ... Vortex Viper PST riflescopes use a fast focus eyepiece designed to quickly and easily adjust the focus on the riflescope’s reticle. Vortex 875874007468 PST-2105 Viper PST Gen II 2-10x32 FFP EBR-4 MRAD The scope that we demoed to go with the Seekins Precision SP-10 rifle (MSRP $2550) was the Viper PST Gen II 3-15×44 FFP (EBR-2C MOA reticle).). To adjust the reticle focus: 1. On the outside of the parallax knob is the knob to turn on the lighted reticle. 2. This scope is Vortex’s second highest tier in regards to price point and optical clarity.