A calibration system for a detector responsive to electromagnetic radiation, the calibration system comprising: a base member; a plurality of radiation sources (304, 304A, 304B, 304C) fixedly attached to the base member, each radiation source (304, 304A, 304B, 304C) being maintained at a different temperature or intensity level and configured to emit electromagnetic radiation; and a positioning mechanism attached to the base member, characterized in that the positioning mechanism comprises: a movable member in form of a partial-disk shaped structure, such as a quarter-disk shaped structure or a half-disk shaped structure, having a single rotatory degree of freedom with respect to the base member, and a plurality of optical elements (310, 310A, 310B, 310C) arranged on the movable member, and the movable member with the plurality of optical elements (310, 310A, 310B, 310C) is configured to be movable between at least two calibration positions and a non-calibration position, wherein, when one of the optical elements (310, 310A, 310B, 310C) is in the corresponding calibration position, the optical element (310, 310A, 310B, 310C) is configured to receive the electromagnetic radiation from one of the radiation sources (304, 304A, 304B, 304C) and to reflect the electromagnetic radiation to the detector, and the other optical elements and radiation sources are in non-calibration positions, where they do not reflect electromagnetic radiation to the detector. a base member; a plurality of radiation sources (304, 304A, 304B, 304C) fixedly attached to the base member, each radiation source (304, 304A, 304B, 304C) being maintained at a different temperature or intensity level and configured to emit electromagnetic radiation; and a positioning mechanism attached to the base member, characterized in that the positioning mechanism comprises: a movable member in form of a partial-disk shaped structure, such as a quarter-disk shaped structure or a half-disk shaped structure, having a single rotatory degree of freedom with respect to the base member, and a plurality of optical elements (310, 310A, 310B, 310C) arranged on the movable member, and the movable member with the plurality of optical elements (310, 310A, 310B, 310C) is configured to be movable between at least two calibration positions and a non-calibration position, wherein, when one of the optical elements (310, 310A, 310B, 310C) is in the corresponding calibration position, the optical element (310, 310A, 310B, 310C) is configured to receive the electromagnetic radiation from one of the radiation sources (304, 304A, 304B, 304C) and to reflect the electromagnetic radiation to the detector, and the other optical elements and radiation sources are in non-calibration positions, where they do not reflect electromagnetic radiation to the detector. a movable member in form of a partial-disk shaped structure, such as a quarter-disk shaped structure or a half-disk shaped structure, having a single rotatory degree of freedom with respect to the base member, and a plurality of optical elements (310, 310A, 310B, 310C) arranged on the movable member, and the movable member with the plurality of optical elements (310, 310A, 310B, 310C) is configured to be movable between at least two calibration positions and a non-calibration position, wherein, when one of the optical elements (310, 310A, 310B, 310C) is in the corresponding calibration position, the optical element (310, 310A, 310B, 310C) is configured to receive the electromagnetic radiation from one of the radiation sources (304, 304A, 304B, 304C) and to reflect the electromagnetic radiation to the detector, and the other optical elements and radiation sources are in non-calibration positions, where they do not reflect electromagnetic radiation to the detector.