Regra Sunny-16

Sunny 16: exposure without a meter

The Sunny 16 rule lets you expose a frame correctly with no light meter at all. Bright daylight? Set f/16 and a shutter speed of 1/ISO seconds. So at ISO 100 you'd shoot 1/100 s at f/16, or the nearest stop your camera has, 1/125 s. When clouds roll in you open the aperture: f/11 for slightly overcast, f/8 for overcast, f/5.6 for heavy overcast or open shade, f/4 at sunset, and f/2.8 for backlit subjects. Reciprocity is what keeps the exposure the same as you move across stops: 1/100 @ f/16 = 1/400 @ f/8 = 1/1600 @ f/4 — the total light is identical, only the depth of field and motion blur change.

Applications

It earns its keep in film photography, on older bodies that never had a built-in meter like the Leica M3 or a Holga. It's a backup when metering fails too, say a dead battery or a high-contrast scene that throws the meter off. Teachers lean on it in photography classes to get the exposure triangle into students' heads, and it gives you a fixed reference in full manual mode (MTM) when you'd rather not hand the decision to auto exposure.

FAQ

Does it work at any latitude? It's tuned for sunlight between 10 am and 4 pm at mid-latitudes. Near the equator or up in the polar regions you'll have to adjust by feel.

And in winter snow or beach? Surfaces that reflect a lot of light throw the rule off, so stop down +1 stop (go to f/22) or the bright surface blows out.

Is it accurate enough for slide film? Negative film forgives a lot, around ±2 stops of latitude. Slides like Velvia or Provia don't, so treat Sunny 16 as a starting point and bracket your shots.