Objective (optics)

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An objective in optics is the lens or mirror in a microscope, telescope, camera or other optical instrument, that receives the first light rays from the object being observed. The objective is also called the object lens, object glass, and objective glass.

Microscope objectives are typically designed to be parfocal, which means that when one changes from one lens to another on a microscope, the sample stays in focus. Photographic zoom lenses may also be parfocal, so that one can change the magnification without having to refocus.