The objective lenses of a compound light microscope are attached to a rotating nosepiece, also known as a turret or revolver. This allows the user to easily switch between objective lenses of different magnifications without having to manually remove and replace the lenses. The nosepiece is typically located on the underside of the microscope's head, and it can be rotated by turning a knob or lever on the side of the microscope. The objective lenses are screwed into the nosepiece and are held in place by a locking mechanism. When the nosepiece is rotated, the objective lens that is currently aligned with the eyepiece is positioned over the specimen, allowing the user to view the specimen at the desired magnification.