A concave mirror would project a real inverted image of the silverpoint onto the panel, which van Eyck would trace. 凹面镜把颠倒的实像投射到木板上,于是范艾克便可以在板子上描画。
As a practical example, an astigmation corrected scanning flat holographio concave grating (SFHCG) is designed and some results of the numerical and optical experiments are given. 给出一消像散SFHCG的设计实例和用这块光栅所做的实验结果。