2005-02-28:

Sunny-16 revisited

Lest I lose it again!

When caught without a meter, one can use the “Sunny 16 Rule” as a guide for exposure. There are two steps to the rule, as outlined below:

STEP 1:
Set your shutter speed equal to your film speed. (i.e., Shutter = Film Speed)

Examples: 1/60 for Velvia rated at ISO 50; 1/125 for TMax rated at ISO 100. Note that in most cases, the shutter speed will NOT EXACTLY EQUAL film speed, but will be set as close as possible to the film speed. It’s simply easier to remember the rule as “Shutter = Film Speed.”

STEP 2:
Set your aperture equal to f/16 for sunny sky.

What if it’s not sunny?
If slightly overcast, open one stop to f/11. If overcast, open two stops to f/8. If deeply overcast, open three stops to f/5.6.

How do I distinguish between slightly overcast, overcast and heavy overcast?
Examine the shadow detail. If shadows are distinct but soft around the edges, then it’s slightly overcast. If shadows are not distinct, but still visible – very soft – then it’s overcast. If there are no shadows at all, then it’s heavy overcast.

The chart below provides a useful summary:

Aperture Lighting Conditions Shadow Detail
f/16 Sunny Distinct
f/11 Slight Overcast Soft around edges
f/8 Overcast Barely visible
f/5.6 Heavy Overcast No shadows
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