Final answer:
The passage implies that Benjamin Franklin's bifocals were not perfect by discussing the limitations and imperfections of optical devices of the era, such as lenses and mirrors known to distort images, and the problems of correcting astigmatism in eyewear.
Step-by-step explanation:
The passage does not explicitly describe the imperfections of the bifocal lens system created by Benjamin Franklin. However, by examining the context around lenses and optical instruments of the time, we can infer that like any early optical technology, the bifocal lens system likely had limitations. Optical devices such as lenses, mirrors, and prisms were known to distort images, causing issues like enlargement, reduction, inversion, or dispersion of light. Galileo's skepticism about telescopic observations until verified by repeated experiments suggests that contemporaneous trust in optical devices wasn't absolute, thus implying Franklin's bifocals weren't perfect. Also, astigmatism, an irregularity that can affect the focus of the eye and therefore how well a lens corrects vision, illustrates that even with corrections, the technology wasn't flawless. And contemporary findings that even the best telescope mirrors have slight imperfections support the idea that no optical system is without its faults, including Franklin's bifocals.