the lab

Reciprocity

camera arithmetic for slow light

Reciprocity is photography's oldest trade: half the light, twice the time. These three panels only work the trade out — through dark glass, under the turning sky, and across a long scene folded into seconds. The film corrections are the makers' published fits; the star ceiling is the NPF rule. And for when the light itself will fall, the light almanac is next door.

free, no accounts, always — if it earns a place in your day, you can buy me a coffee.