The Sunny 16 Rule

No light meter? No problem

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Left your light meter behind?

Batteries are flat?

Don't panic!

The Sunny 16 Rule is a way to estimate daytime photography exposure without using a light meter.

The basic rule is this: on a bright, sunny day set your aperture to f/16 and the shutter speed to the reciprocal of your film's ISO. For example, if you are using ISO 100 film, set the shutter speed to 1/100" - or the nearest value, probably 1/125". If you are using ISO 400 film, set your shutter speed to 1/400" (or nearest value).

The clue is in the shadows. Look around at the shadows on the ground. If the shadows are distinct with fairly solid edges then use f/16, if the shadows are softer but noticeable open the aperture to f/11. Looking out my window here today it looks rather gloomy and overcast... it's an f/5.6 kind of day for sure.

f/16		Bright sun - strong shadows with distinct edges
f/11		Cloudy - noticeable shadows with soft edges
f/8		Overcast - faint shadows
f/5.6		Heavy Overcast - no shadows
f/4		Sunset - no shadows

I find it a good practice to use Sunny 16 to estimate the exposure value before I take a meter reading. I do this for two reasons, the first is to make sure my meter reading is in the right ball park and I haven't made a mistake, the second reason is - it's kind of fun.

But what if you want to shoot at f/8 and it is bright and sunny? No problem there either. Just remember the Law of Reciprocity. If you need to open the aperture by two stops then increase the shutter speed by two stops to compensate and produce an equivalent exposure.

Here are a few examples with shutter speeds adjusted to the nearest likely value:

Sunny 16	Equivalent Exposures
ISO 100 - f/16 @ 1/125" Bright sun, strong shadows	f/11 @ 1/250"	f/8 @ 1/500"	f/5.6 @ 1/1000"
ISO 200 - f/8 @ 1/250" Overcast, average light	f/5.6 @ 1/500"	f/11 @ 1/125"	f/16 @ 1/60"
ISO 400 - f/4 @ 1/500" Sunset, no shadows	f/5.6 @ 1/250"	f/8 @ 1/125"	f/11 @ 1/60"

If using negative film I would normally use a shutter speed around a half to a full stop slower than the above table. It's better to over-expose than under-expose so choosing a slower shutter speed leaves a margin of error.