The optical system consists of three main optical assemblies:
Objective lens assembly. This is the lens assembly at the front of the binoculars. It gathers light from the object and forms an image at the image plane.
Image orientation correction assembly. This is usually a prism assembly that shortens the optical path. Without this, the image would be inverted and laterally reversed, which is inconvenient for the user.
Eyepiece lens assembly. This is the lens assembly near the user's eyes. Its function is to magnify the image.