Optical design of athermalized infrared telephoto objective

One method for athermalized infrared telephoto objective design was proposed. First, by synthesizing the formulated athermal model for the multiple-lens optical system with telephoto objective model, the optical power distribution equations were established. Thus, the initial optical power distribution among lens could be resolved with consideration of the telephoto ratio requirement and lens material constraint. Then, a final routine computer-aid modification procedure would help to correct the optical systems aberrations. This systematic design method was straightforward and applicable. As practical examples, a mid wavelength infrared optical system and a long wavelength infrared optical system were designed with ZEMAX software. With the focal length equal to 100 mm and F number equal to 2.0 for both systems, the telephoto ratio reached 0.8. When environment temperature varies from -40 ℃ to 60 ℃, the image preserves high quality and modulation transfer function (MTF) still approaches diffraction limit. The result of the implemented design agrees well with the method predictions.