Structure design and assembling of compensator for off-axis aspheric surface with large asphericity

Three-lens Offner compensator was designed for off-axis aspheric surface with fast ratio and large asphericity. Because tolerance requirement of centering errors and air gap distances is very severe, corresponding barrel structure of compensator is designed. The structure separates line-centering error adjustment and angle-centering error adjustment, which can achieve high accuracy adjustment of the compensator. According to measuring results of center deviation measuring apparatus, finally angle-centering error between compensating lenses is 4.4″, line-centering error is 3.5 μm, and air gap distance error is 3.8 μm.Angle-centering error between compensating lenses series and field lens is 5.3″, line-centering error is 4.2 μm, and air gap distance error is 7.2 μm, which meet the demand of testing.Off-axis aspherical surface is tested by 4D interferometer and the compensator, PVq value is 0.135λ and RMS value is 0.019 5λ, better than designing requirements.