an optical apparatus includes an interchange mechanism and an optical assembly of an illumination system or a projection objective . at least one of the plurality of optical elements of the optical assembly is selected from among a plurality of ones selectable from the interchange mechanism which facilitates exchange of one for another in the beam path . to reduce transmission of vibration from the interchange mechanism to the optical assembly , the interchange mechanism is mounted on a structure which is substantially dynamically decoupled from the housing , and a selected selectable optical element is located at an operating position at which it is separate from the interchange mechanism .