Lens is the most basic optical element that constitutes the optical system of a microscope. Components such as objective lens, eyepiece, and condenser lens are composed of a single or multiple lenses. According to their different shapes, they can be divided into two categories: convex lenses (positive lenses) and concave lenses (negative lenses).

Optical glass is the main raw material for lens production due to its high transparency, purity, colorless, uniform texture, and good refractive ability. Due to different chemical composition and refractive index, optical glasses include flint glass, crown glass, and lanthanum crown glass.