The Sunny f16 rule

Just in case you ever wondered:

The Sunny f16 rule: this is a great thing to fall back on if you have a manaul camera and the battery dies. Nowadays with digital it's only use its to let you know if your exposure is going to be way off. E.g. when shooting subjects with a lot of black or of white in; or if you have no spot meter when shooting say a white bird against a deep shadow.

The idea is that on a clear sunny day, you set the meter to f16 and the shutter speed at the same speed as the ISO.

I.e. if you are using ISO/ASA (film speed) of 400, then the shutter speed should be 400th sec at f16, if the ISO is 100 then it's 100th sec at f16.

Lets say you're using 100 film speed (ISO/ASA 100) - If you want to use f8 for example instead of f16 then you just adjust the shutter speed to match: i.e. here wee would be using a wider aperture by 2 stops, (f16 to f8 ) = so shutter speed is increased by 2 stops so the same amount of light gets through -so it would be f8 at the ISO speed plus two stops e.g. (with ISO 100 film speed/sensor sensitivity) it would normally be f16 at 100th sec shutter speed, so it could also be f8 at 400 shutter speed or any other combination , e.g going the other way f22 at 50sec shutter speed.

Thus on a clear sunny day: for every f-stop you open up you set a shutter speed double (i.e. HALF the time , that is, one stop less) what it was when the same as the ISO setting OR for every f-stop you close down the aperture you set a shutter speed half the speed (i.e. TWICE the time it's open = one stop) what it was when the same as the ISO setting.

Examples at ISO 100:
f32 @ 25th sec
f22 @ 50th sec
f16 @ 100th sec
f11 @ 200th sec
f8 @ 400th sec
f5.6 @ 800th sec

Examples at ISO 400:
f32 @ 100th sec
f22 @ 200th sec
f16 @ 400th sec
f11 @ 800th sec
f8 @ 1600th sec
f5.6 @ 3200th sec

If it's not a clear sunny day it becomes pretty much guess work but it's still a good starting point;-)