Magnix

Meet Magnix, a magnifying glass who makes tiny things look big when you hold her close.

Your eye cannot focus on anything closer than its near point, about 25 cm for a typical adult. That limits how large a small object can look. A converging lens placed just in front of the eye lets you bring the object much closer and still see it sharply.

With the object at the focal point, the lens sends parallel rays into a relaxed eye, and the angular magnification is M = 25 cm divided by the focal length f. A lens with f = 5 cm magnifies five times.

A shorter focal length gives more magnification, but strongly curved single lenses blur and add coloured fringes. Most hand magnifiers stop at about 10 times. Beyond that, a microscope with two lenses works better.

Jewellers wear a loupe, stamp collectors carry a pocket lens, and a single drop of water on a leaf acts as a tiny magnifier. Antonie van Leeuwenhoek saw bacteria in the 1670s with tiny single-lens magnifiers.