The camera obscura
A live image of the city on a table, by optics alone.
HombreDHojalata from Spain — CC BY-SA 2.0 · SergioRuPi — CC BY-SA 4.0 · Emilio J. Rodríguez Posada — CC BY-SA 3.0 · Emilio J. Rodríguez Posada — CC BY-SA 2.0
**The highest watchtower in Cádiz — with a camera obscura projecting the living city onto a concave table** — in the heart of the old town. ⚠ **Cádiz is a city of towers**: **more than a hundred and twenty watchtowers were built** in the 18th century — ⚠ **not for defence but for trade**: **merchants watched from them for the American fleets** to learn of their cargoes before anyone else. ✅ **And Tavira was the official watchtower** from 1778. ✅ **The camera obscura is the object**: **a darkened room with a lens and mirror in its roof** ⚠ **casting a live, moving image of the city onto a white concave table** — **cars passing, people walking, washing stirring** — ✅ **with no electricity and no screen**, **by optics alone**. ⚠ **Shows run at set times with a guide.**
A live image of the city on a table, by optics alone.
A view over the old city and ocean on every side.
Dozens of others visible from here above the roofs.
Calle Marques del Real Tesoro 10, 11001 Cadiz, Spain
**The oldest principle in photography — a lens, an aperture and a dark room, with no electricity and no screen.** ✅ **The principle**: ⚠ **pierce the wall of a completely dark room with a small hole**, **and the light entering draws an image of the scene outside on the opposite wall** — ⚠ **upside down**; **because the rays cross at the hole**. ✅ **This has been known since antiquity** — ⚠ **and Ibn al-Haytham described it precisely in the *Book of Optics* in the 11th century**, **the first to explain it correctly in optical terms**; **and the word *camera* is simply Latin for «room»**. ✅ **The refinement**: **replacing the hole with a lens** gives a **brighter and sharper image**; **and adding an angled mirror at the top** ⚠ **reflects the image downwards and corrects its orientation** — **so it falls on a horizontal table**. ✅ **The table is concave** because the projected image is not perfectly flat — **so the curve keeps it sharp across its whole area**. ✅ **The result**: **a live, moving, colour image of the city** — ⚠ **not a recording but what is happening now**; **you watch a car pass and a bird fly**. ⚠ **It needs strong light** — **which is why an overcast day weakens it**.
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