The “sunny 16″
rule is a way of manually calculating exposure and aperture based on lighting
conditions and film ISO.
While there isn’t a great call for knowledge of this rule with today’s
automatically metered cameras and digital sensors, it is a rule I have played
with, set the camera to manual and gotten surprising results, sometimes even
better than the cameras automatic exposure control!
The Sunny 16 rule is a fairly accurate means of estimating an exposure when
there are specific lighting conditions for middle toned subjects.
The rule is this:
If you have bright, over-the-shoulder sunlight casting sharp, distinct shadows,
and you have a middle toned subject with the cast shadows falling directly away
from the camera, you can make a fairly accurate exposure by setting your lens at
f/16 and your shutter speed at the reciprocal of your film’s ISO. If that’s ISO
100, then the reciprocal is 1/100th sec, or the nearest full shutter speed,
1/125th second. I know, that’s a third less light, but this is an estimated
exposure, remember? It might not be perfect, but it will get you close when you
need it.
These numbers all change based on the aperture used, F11, which has twice the
light of F16, requires a shutter speed of 1/200th (will actually be 1/250th on
most cameras)
F8, which has 4x the light of F16 will require 1/500th etc.
Changing film to ISO 50, will result in the shutter speeds needing to be longer.
F16 @ ISO 50 will require a shutter speed of 1/60th.
F16 @ ISO 200 will require an exposure time of 1/250th.
And of course, if you know the shutter speed you want to use, you can use the
same formula to calculate the best aperture to set to obtain that speed, again
based on light conditions and film / sensor ISO.
Let’s assume an F stop of f/8 and a ISO (film speed) of 400. Here’s what these
10 light levels are and the shutter speed that would be needed.
A Sunny day outdoors @ 1/2000 sec
A hazy bright day @ 1/1000 sec
A bright cloudy day without shadows @ 1/500 sec
An overcast day, or open shade on a sunny day @ 1/250 sec
A heavily overcast day @ 1/125 sec
Deep shade, under trees on a bright overcast day @ 1/60 sec
Just before a thunderstorm or late on a heavily overcast
day @ 1/30 sec
A brightly lit store interior @ 1/15th sec
A well-lit stage or sports arena @ 1/8th sec
A well-lit home interior @ 1/4 sec