What is the "franklin plane" in reference to photography?

Answer 1

You probably mean focal plane. And this would be a lot easier to explain if I could draw here. When parallel rays of ;light pass through a lens they converge at a central point somewhere between the rear element of the lens and the film plane. This is called the rear focal plane. At the focal plane they cross and then diverge and form an image at the film plane

Answer 2

Nothing related to photography.