A charged-particle optical system (100) such as an electron microscope has a vacuum chamber (102) with a space (104) for accommodating a specific one (114) of multiple specimens in operational use. The charged-particle optical system has a loader (106) with a part (108) that is moveable into and out of the space. The part is configured for attaching a specimen carrier (110), brought from outside the system, to a first holder (112) or to detach the carrier from the first holder and to remove the carrier from inside the system. The carrier accommodates a first specimen. The system has an interface (116) in a wall of the chamber for removably accommodating the first holder (112) or a second holder (118) with a second specimen (120) mounted thereon.