红外双反射镜折转光学系统的MTF测量

MTF Measurement Method For Infrared Dual-Mirror-Refracted Optical System

为了压缩总长度,红外热像仪普遍采用双反射镜折布局(U型)及箱式壳体,而现有传函仪仅能测量非折转布局(一字型)的光学系统的调制传递函数(Modulation Transfer Function,MTF),导致传函仪无法接到U型光学系统的像面,因此无法测量其MTF。为了解决该难题,本文采用光瞳衔接的方式,设计和加工一个中继镜组把U型光学系统的像面引出,通过测量组合系统的MTF,再计算出U型光学系统的MTF,从而解决其MTF测量的难题。然后使用6个同一个型号的红外热像仪对测量方法进行验证,在排除影响测量的干扰因素以后,通过测量组合系统MTF,再计算出U型光学系统的MTF。同时,在测量过程中发现5#、6#红外热像仪的U型光学系统的MTF下降较多,通过红外中心偏差测量仪的测量,发现第三、四镜片的中心偏差较大,故重新装调和控制,从而使U型光学系统的MTF有大幅提升。该方法为U型光学系统的MTF测量和性能提升提供了新的思路。

To compress their total length,infrared thermal imagers commonly have a double-reflector folded layout(U-shaped)and a box-shaped shell.Existing transmission instruments can only measure the modulation transfer function(MTF)of optical systems with a non-folded(straight)layout owing to the inability of the transmission instrument to receive the image plane of U-shaped optical systems.To solve this problem,this study used the pupil connection method and designed and processed a relay lens group to direct the image plane of the U-shaped optical system.The MTF of the U-shaped optical system was calculated by measuring the MTF of the combined system,thereby solving the MTF measurement problem.Six infrared thermal imagers of the same model were used to verify the measurement method.After eliminating the interference factors affecting the measurements,the MTF of the U-shaped optical system was calculated by measuring the MTF of the combined system.During measurement,the the U-shaped optical system MTF of infrared thermal imagers 5 and 6 decreased significantly.Using an infrared center-deviation measuring instrument,it was found that the center deviations of the third and fourth lenses were relatively large.Therefore,they were reinstalled and controlled,resulting in a significant improvement in the MTF of the U-shaped optical system.This method provides a new approach for MTF measurement and performance improvement in U-shaped optical systems.