What is "eyepieces"

Usage examples of "eyepieces".

He positioned it over the neck bones of the deformed skeleton, peered through the eyepieces, made a few adjustments, then stepped back.

Harry worked with a series of eyepieces, adjusting the power on the scope and trying to sharpen the focus, until he had pulled in so close to the window that the lens was filled by the narrow slot between the drapes.