Hockney and Falco explain this shift as follows: van Eyck traced part of the image projected in an epidiascope, then accidentally bumped the silverpoint, the oil or the mirror, and finally traced the remaining, now shifted, image.

• 霍克尼与法柯对此位移的解释如下：范艾克用幻灯机描了部份的影像后，不小心碰到银尖笔、油画、或者镜子，然后继续描完剩下已经位移的影像。