主动调焦式航空相机物镜光学设计及温度仿真分析

对流层内,环境温度随海拔高度的升高而降低。为了补偿温度变化对成像质量的影响,设计了主动调焦式航空相机物镜:f=400mm、视场角2ω=10°、F数为8、波段460～750nm、总长380mm、后截距150mm;该物镜在常温常压下,调制传递函数(MTF)fMT≥0.52(70lp/mm),接近衍射极限;各视场弥散斑均方根(RMS)直径大小约3.6μm;该相机包括一调焦组,移动范围为±5mm,调焦组每移动0.1mm,焦平面约移动0.026mm。针对设计结果,随后进行了温度水平分析和温度梯度仿真。对于温度水平分析,在-60℃～+60℃下进行了稳态调焦分析,分析结果表明经调焦组主动调焦后,物镜成像质量与常温下相差不多,可成清晰像;于此同时,相机可在调焦完成后,在温度宽度为±16℃的范围内保证像质。对于温度梯度仿真,人为地对各透镜单独设定温度场得到20℃轴向、径向温度梯度,有限元仿真及相应的计算结果表明,经主动式温度调焦后,在温度梯度情况下,相机物镜依然保证成像清晰。

Optical Design and Thermal Analysis for the Active-Focusing Aerial Camera Objective

In the troposphere, the higher the altitude ascends, the lower the temperature is. To compensate the influence of the change of temperature upon the image quality, an active-focusing aerial camera objective is designed, for which f is 400 mm, field of view 2ω is 10°, F number is 8, wavelength range is 460～750 nm, total track is 380 mm and back focal length BFL is 150 mm. This objective has perfect resolution, whose modulation transfer function fMT is no less than 0.52 at 70 lp/mm and the root mean square (RMS) diameter of the spot is 3.6 μm. A focusing group is equipped in this objective whose motion range is ±5 mm, and the 0.1 mm moving value is responsible for 0.026 mm in the image plane. The stationary thermal analysis and the temperature gradient emulation of the camera objective are presented subsequently. For the stationary thermal analysis, it is showed that after the active focusing, the aerial camera objective can obtain good image quality at the temperature range of -60 ℃～+60 ℃. For the temperature gradient emulation, each lens′ temperature gradient is set artificially which obtains the 20 ℃ axial and radial temperature gradients respectively; the result of the emulation shows that the objective can obtain good image quality at the 20 ℃ temperature gradient by active focusing.