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
Gran Teatro Falla**A red-brick theatre with horseshoe arches — and the stage of Spain's most famo5 minutes walk4.8
Cádiz Cathedral**A cathedral with a yellow dome facing the Atlantic — 116 years in the building6 minutes walk4.6
The Roman Theatre**Spain's second-largest Roman theatre — undiscovered until 1980, by accident, b7 minutes walk4.3
Castillo de Santa Catalina**A star fort on the sea built after the English sacked Cádiz — and entry is fre11 minutes walk4.4**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**.