Focal length measurement for the off-axis TMA space camera

The focal length of the off-axis three-mirror anastigmat(TMA)is one of the most important parameters of the space camera.The focal length measurement for the off-axis TMA space camera is done after the alignment of optical system and the assembly of optical lens.The magnification method and the angle measurement method are two classic methods for the focal length measurement.The angle measurement method is selected by comparative analysis.The calculation formula of the focal length which is applicable to the coaxial optical system is modified by adding the off-axis angle.Thus,it is applicable to the off-axis TMA optical system.Besides,the method and the procedure for the focal length measurement are discussed by the example of the focal length measurement for the off-axis TMA space camera.The focal length of the space camera is 8 010 mm,calculated by the modified formula of the focal length.The feasibility of the method of the focal length measurement for the off-axis TMA is confirmed.