A feed device for an immersion medium for use with an objective enabling a specimen to be imaged microscopically includes a cap fitted releasably or fixedly to the objective and delimiting a receptacle space for the immersion medium. The cap has an exit opening aligned with an optical element of the objective facing the specimen. The immersion medium held in the receptacle space is feedable through the exit opening to a target space situated between the optical element of the objective and the specimen. A sensor is integrated in the cap and has an electrode structure configured to detect an amount of the immersion medium fed through the exit opening to the target space. The electrode structure at least partly encloses the exit opening and has a spatial detection region extending away from the exit opening in a radial direction.