The Eye as a Camera

Focusing with a living lens

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Power in dioptres: $P = 1/f$, and $P = \frac{1}{d_o} + \frac{1}{d_i}$.
• The eye adds power (accommodation) to focus on near objects.
• Short sight needs negative lenses; long sight and age need positive ones.
• The cornea does most of the focusing, but only in air.

Steps

1. Dioptres
2. Focus on the page
3. Short-sighted
4. Reading glasses
5. The eye’s focal length
6. Blurry underwater