My finding about the unlikely focal length of the putative projection mirror has a second implication, even more constraining to the Hockney theory. 既然设想中投射镜的焦距不太可能实现，我的发现还延伸出第二个推论，更使霍克尼的理论受限。
Given the surviving records for all manner of other optical systems and mechanical drawing aids, the absence of evidence for the Hockney projector is difficult to explain. 其他光学系统与绘图辅助工具的记录，到今天都还留存了不少，为何唯独缺乏霍克尼投影设备的证据，显然很难解释。
