空间三反相机调焦范围的确定

Focusing range of space off-axial TMA optical camera

为了提高空间相机对温度的适应能力,改善相机成像质量,研究了如何通过调焦放宽相机的热控指标,降低相机热控难度的问题。推导出了纯反射离轴三反光学系统中后截距及相机受温度影响下焦面离焦的数学公式;分析证明了相机离焦量与温度变化是线性关系,并计算得到了常数项K值。计算显示,当反射镜材料的线胀系数与相机支撑框架材料线胀系数一致时,焦面不产生离焦;而两种材料线胀系数差距越大,离焦量就越大。利用离焦传递函数公式证明了当相机温度水平变化超过±1℃时(对应离焦量0.05mm),就必须采用机械调焦的方法对其加以补偿;利用光机热集成仿真的方法,得出保证相机成像质量的温度范围Δt,完成了从光学指标到温度指标的转换。利用离焦公式,得出了相机的调焦范围。最后,在热真空环境下试验验证了上述焦面离焦的数学公式及相机温度水平变化±4℃时离焦量为±0.184mm是相机合适的调焦范围。

To improve the adaptive capacity of a space camera to environment temperatures and to en- hance its imaging quality, this paper explores how to implement the thermal control by relaxing ther- mal control indictors. A mathematical formula of intercept and defocus affected by temperatures is de- rived for a pure off-axls Three Mirror Anastigmatism（TMA） optical system. The analysis shows that camera defocus amount and temperature are a linear relationship, Then, a constant K value is calcu- lated. Furthermore, it indicates when reflector and camera structures have the same coefficient of line- ar expansion, the defocus does not occur. However, the greater the difference between two material linear expansion coefficients is, the greater the amount of defocus is. With defocusing formula, it sug- gests that mechanical focusing methods must be used to request for compensation when the camera temperature level changes more than ± 1℃ （corresponding to the defocus amount of 0.05 mm）. U- sing integrated photo-thermal simulation method , the temperature range At is obtained to ensure the image quality of the camera. Finally, camerars focus range is derived by using the formula of defocus. The result of defocus test under thermal vacuum environment verifies the correctness of the defocus formula and the defocus amount of 4- 0. 184 mm is a proper focus range corresponding camera temper- ature levels changed in q- 4 ℃.