Rifle Optics Glossary
Last updated: April 16, 2026
Every term in bold appears in our reviews or comparison tool. Bookmark this page — most of the reticle-math questions shooters have are answered below.
- MOA
- Minute of Angle. 1 MOA subtends roughly 1.047 inches at 100 yards. Common on American scopes.
- MRAD (Mil)
- Milliradian. 1 MRAD subtends roughly 3.6 inches at 100 yards (10 cm at 100 m). Common on European and precision scopes.
- FFP
- First Focal Plane. The reticle scales with magnification — holdovers are accurate at any zoom.
- SFP
- Second Focal Plane. The reticle stays the same size. Holdovers are only accurate at one specified magnification (usually max).
- Parallax
- Apparent reticle movement when the shooter's eye shifts behind the scope. Precision scopes have a parallax-adjustment knob or side focus.
- Eye Relief
- The distance from your eye to the ocular lens where you get a full image. Critical on recoiling rifles.
- LPVO
- Low-Power Variable Optic. A variable scope starting at 1x — the fighting rifle sweet spot.
- Prism Scope
- A fixed-magnification optic using a prism instead of erector tubes. Has an etched reticle that works without batteries.
- BDC
- Bullet Drop Compensator. A reticle with holdover marks calibrated for a specific load and caliber.
- MIL-STD-810
- US military durability standard for shock, vibration, and environmental extremes. Pass claims are common marketing — verify the specific test battery.