I just won a Seneca Rapid Rectilinear lens off our favorite auction site. It's listed as an f/8, with focal length around seven inches. I'm going to assume that f/8 here isn't the same as f/8 in the modern system. Does anyone know which older system was used? I know I've seen tables for converting to modern f-stops. Also, has anyone used the Seneca lenses? I've read that the Rapid Rectilinear design was good, and that Edward Weston used one, but I haven't seen any info about Seneca in particular.