Measuring The Focal Length Of Transmission Lens Using F-P Etalon

The main measurement method of focal length of transmission objective lens is magnification method,which is restricted by parallel light tube.It is difficult to improve the accuracy of focal length of objective lens and trace its origin.Here,a new method for measuring focal length of transmission objective lens based on Fabry-Pérot(F-P)etalon is studied.A series of conical beams produced by monochromatic light transferring through a F-P etalon is used as the standard light beams for measuring.The standard light beams transfer through the transmission objective lens(which is to be measured),and image into concentric rings under the known law in the focal plane.Because the multi-wavelength excess fraction method of the standard spectral line can accurately measure the F-P standard interval and is used to calculate the parameters of the concentric ring with known rules,the method has the self-calibration characteristic.The thesis mainly completes the following work.(1)Based on the principle of multi-beam interference in F-P etalon,the characteristics and rules of imaging concentric rings with F-P etalon are analyzed.The principle and method of focal length measurement using F-P etalon are studied.The theoretical calculation and calculation model for the focal length of transmission objective is derived by regression calculation.At the same time,the self-calibration measurement method of focal length is analyzed and discussed.(2)According to the characteristics of imaging concentric rings,the data processing method of plane array image information is studied deeply.A method of interpolation,subdivision and smoothing of the plane array pixels is proposed and implemented,which reduces the systematic error caused by pixels.The peak point coordinates are subdivided by regression calculation method,and the measurement accuracy is further improved.(3)Based on the focal length measurement model,an experimental device for focal length measurement is built.The mercury's green line is used as the measurement wavelength,and the interference rings are processed by using the plane array image information data processing method.The focal length measurement of the 75 mm is conducted as while the uncertainty components of focal length measurement are analyzed and calculated and the influence of focusing error on the focal length measurement is studied deeply.The experiment results show that the relative expanded uncertainty of the objective lens is 0.031% when using the measurement unit of w?(the virtual pixel interval of the plane array device)and the self-calibrated relative measurement value of lens focal length is f w?= 63711.9.Further discussion is made on the improvement of the measurement experiment and the optimization of the pixel interval w calibration scheme,and the relative expansion uncertainty of the focal length can be reduced further after the implementation of the scheme.