There's a term that I've been seeing over and over in the latest rounds of lens announcements: apochromatic or APO lenses. But what are APO lenses, and does the tech really matter, or is it all hype?
Light travels at different speeds based on the medium it passes through. For example, in a vacuum, it travels at 3.0 × 10^8 m/s in a straight line. But when directed towards glass, air, diamond, water ...