Reticles are circular, transparent glass elements with a system of lines, dots, circles, or crosshairs for fine measurement or alignment in sighting applications. Reticles are used in sighting devices such as telescopes, microscopes, telescopic sights, and oscilloscope screens. Most reticle designs are etched, holographic, or made from wire. Etched reticles may have floating elements that do not cross the reticle itself. These optical devices are suitable for ballistics and range estimation applications. Holographic reticles are illuminated by a laser diode to produce three-dimensional (3D) images. Wire reticles feature lines that cross the reticle completely. The shapes or patterns are limited by the thickness of the wire, which is usually black or silver.
Reticles may be positioned at either a scope’s front focal plane or its rear focal plane. With fixed power scopes, the location is not critical. With variable power scopes, however, the location determines whether the reticle remains at a constant size to either the target (front plane) or user (rear plane). The first focal plane is associated with the objective lens and the second focal plane is associated with the ocular lens. Sometimes, sighting devices are referred to as either first focal plane reticles and second focal plane reticles. Although front-plane reticles provide greater durability, many variable power scopes feature a rear focal plane design.
Product specifications for reticles include diameter or side length, line width or graduations, and thickness. Centering, the displacement error of the reticle design from the center, is also important to consider. Typically, reticle suppliers categorize products by type, which is based upon the shape or pattern. There are many different types or styles of reticles. Some have patterns that consist of concentric circles. Others have crossed lines or crosshairs. Choices may include grid patterns, single or multiple horizontal lines, pinwheels, and protractors. Reticles with scales, spots or dots, and single or multiple vertical lines are also available. Whipple reticles use a grid pattern with a single grid that is further divided into a varying grid.
Specialized reticles are available for ballistics, firearms, and gun sighting applications. The tactical military reticle (TMR) is a variation of the Mil Dot design. It features vertical and horizontal crosshairs with tick marks or lines that are variously sized and spaced. Special purpose reticles are specialized sighting devices that combine the features of range finding reticles with other designs, grids, or patterns. Microscope reticles for laboratory or scientific application are also available.