The diagram does not consider additional constraints: decreased resolution due to diffraction and increased susceptibility to fixed pattern noise with longer exposures.
图表没有考虑其他限制因素：衍射造成的低分辨率，长时间曝光带来的对固定图形噪声的敏感性。
2
For infrared optical systems a point spread function is calculated in terms of the spot diagram obtained through geometrical ray trace or the theory of Kirchhoff diffraction.