The physics

How photography works

Short explainers of the science behind the timeline, each linked to the inventions that put it to use. Each primer has an interactive diagram to try.

1. 01Light and the pinholeWhy a hole in a dark box makes a picture, why it is upside down, and why the hole can be too small as well as too big.
2. 02Refraction and lensesHow glass bends light to a point, why focal length sets how much of the world a picture takes in, and why lens design took a century of maths.
3. 03Aperture and f-numbersWhy f/2.8 lets in twice the light of f/4, why the zone of sharp focus deepens as the opening shrinks, and why stopping down too far softens everything.
4. 04ExposureHow aperture, shutter speed and sensitivity trade against each other, what an exposure value is, and why old rules of thumb like 'sunny 16' still work.
5. 05Silver halide chemistryHow a few photons leave an invisible mark in a silver crystal, how a developer multiplies it millions of times, and why fast film is grainy.
6. 06ColourWhy three colours are enough, why light and dyes mix in opposite ways, and why a white shirt looks orange under a light bulb in a photograph but not to the eye.
7. 07Digital sensorsHow a chip of silicon counts light, how one colour per pixel becomes a full-colour image, and why noise is a law of physics, not a flaw.
8. 08Format, crop factor and equivalenceWhy sensor size changes what a lens sees, what 'full frame' and 'APS-C' really mean, and how to compare lenses across formats.
9. 09Computational photographyHow phones beat the limits of tiny sensors by merging many frames, why that works, and how software now shapes, and can fake, the photograph.