In practice, these situations can only be approached but not achieved because the effects of any surface imperfections in the reflectors propagate and magnify, absorption gradually extinguishes the image, and any observing equipment (biological or technological) will interfere.
实际中，这些情形只能去趋近却不能去达到，因为反射器表面的任何瑕疵造成的影响都会增加、放大，而对光的吸收会逐渐使图像黯淡、消失，而且所有的观测设备（生物的或技术的）都会有干扰。