A lithographic apparatus includes a masking device that includes a first masking part configured to obscure a first part of a first patterning device before the pattern of the first patterning device is impinged by a radiation beam, a second masking part having an adjustable length, the second masking part configured to obscure a second part of the first patterning device after the pattern of the first patterning device is impinged by the radiation beam and to obscure a first part of a second patterning device before the pattern of the second patterning device is impinged by the radiation beam, and a third masking part configured to obscure a second part of the second patterning device after the pattern of the second patterning device is impinged by the radiation beam.