Figure 5.1 – Cross-tab of Focal Length and Image Size

This cross-tabulation shows a rough correlation between image size and focal length of the lens across a variety of optical boxes. My colleague Ana David Mendez and I have been collecting this data as part of a project to create a taxonomy of optical boxes that encompasses their full variety. The case numbers in this table are relatively small because focal length is rarely reported in museum catalogues and we have to measure it ourselves which involves first getting permissions then travelling to museums and collections around Europe.