Refractors are optical instruments that use lenses to bend and focus light, allowing for the observation of distant objects. They are commonly used in telescopes, where the primary lens, known as the objective lens, gathers light and brings it to a focus. This design provides clear and sharp images, making refractors popular among amateur astronomers and professionals alike. The design of refractors has evolved over time, with advancements in lens technology improving image quality and reducing chromatic aberration. Famous refractors include the Yerkes Observatory telescope, which features a large objective lens, showcasing the capabilities of this type of telescope in astronomical observations.