Eyepieces are optical components used in devices like telescopes and microscopes to magnify images for viewing. They are typically located at the end of the instrument where the user looks through. Eyepieces come in various designs and magnification levels, allowing users to adjust the view according to their needs. The most common types of eyepieces include Huygens, Kellner, and Plössl, each offering different fields of view and image quality. The choice of eyepiece can significantly affect the overall viewing experience, making it essential for users to select the right one for their specific application.