crosshairs

A crosshair is a set of intersecting lines used as an aiming point or alignment reference in optical instruments. They are commonly found in riflescopes, telescopes, cameras, surveying instruments, microscopes, and certain medical or laboratory devices. The term describes the central cross formed by two perpendicular lines, though reticle designs vary widely.

The reticle is typically located in the instrument’s reticle plane, often at the focal plane, so the cross aligns with the target when viewed through the optic. Designs range from simple, unobtrusive lines to more complex patterns that include dots, circles, or grids to aid precision and measurement.

Reticles fall into several primary categories. Wire reticles use thin metal wires; etched glass reticles are laser-cut or etched onto glass substrates; holographic reticles employ diffractive patterns produced by holography. Illumination is common in modern reticles, using LEDs or fiber optics to improve visibility in low-light conditions.

Applications span multiple fields. In firearms and archery, crosshairs assist aiming and often incorporate markings for range estimation, windage, and elevation adjustments, sometimes with ballistic compensation scales in MIL or MOA units. In astronomy and microscopy, reticles aid alignment and measurement rather than aiming. In photography and video, crosshairs may appear on-screen to indicate subject placement or critical focus.

Etymology traces the term to the notion of fine lines resembling hair; “cross hairs” reflects the hairlike crossing lines. The concept has evolved from early optical sights and surveying tools to modern precision reticles made of wire, glass, or holographic materials.