The objective is the optical element that gathers light from the object being observed and focuses the light rays to produce a real image. Objectives can be a single lens or mirror, or combinations of several optical elements. They are used in microscopes, telescopes, cameras, slide projectors and many other optical instruments. Objectives are also called object lenses, object glasses, or objective glasses.
Microscope lens , eye piece, mirror.
Various size and types are available.