Prologue: Reverse-Engineering the Human Eye — A Fermi EstimationBefore we descend into the mesopelagic abyss, let's ask a basic optical engineering question: What is the F-number of the human eye? This is not something you'll find in most biology textbooks. Optical engineers think in F-numbers. So let's think like one.The Measurement ProblemThe human eye is not a camera—it's a variable optical system. The pupil expands and contracts, so the effective F-number changes throughout the day. But w...
