Photography Sunny 16 Rule
The Sunny 16 Rule simply states that in bright sunlight with an aperture of f/16, your shutter speed should be the reciprocal of your ISO. The Sunny 16 Rule is a rule of thumb means to find the correct exposure without using your camera's metering. This is especially useful if you are shooting with a manual camera that has no built-in light metering.
Let's take the following example: You are outside on a sunny day, you are NOT in the shade, and you dial in your aperture to f/16 and your ISO to 100 (digital or film). What should you set your shutter speed to?
But my camera doesn't have 1/100th, what should I do now?
Answer: Set it to the next fastest setting (in this case, probably 1/125th). You should always round to the next fastest speed, slightly underexposing is better than slightly overexposing.
How To Apply The Sunny 16 Rule
The available light in your scene will of course require you do dial in different settings. So how do you use the Sunny 16 Rule to figure this out?
Here is a simple handy reference chart:
|Sunny with Sand or Snow||f/22|
|Sunny and Clear||f/16|
|Bright Overcast or Slight Shade||f/11|
|Dark Shade or Sunset||f/4|
Remember, the chart above works regardless of what ISO or shutter speed you are using, as long as the shutter speed is the reciprocal of the ISO.
So if you are outside on a sunny day and your ISO is 400 and your aperture is f/16, that means your shutter speed is 1/400th (or 1/500th). If you then venture into a slightly shaded area, you can simply dial your aperture up a stop to f/11. If the sky becomes overcast, you can dial your aperture up another stop to f/8, and so on.
Changing Aperture Indepedent Of Daylight Conditions
While the above chart is a handy guide, it of course does not account for all situations. But using the Sunny 16 Rule as a guide, it's possible to extrapolate any combination of settings for a given daylight condition.
Let's say you want to dial in f/8 instead of f/16 on a sunny day. An aperture of f/8 is two stops up from f/16, so that means you need to adjust your ISO or shutter speed accordingly. For this example we will assume you are using a fully manual film camera, therefore your ISO is fixed to your film speed. In this example, we will be using ISO 400 film. Using the Sunny 16 Rule we know that at f/16 on a sunny day, we would set the shutter speed to the reciprocal of the ISO, so that means a shutter speed of 1/400th (or 1/500th). But now we want to set the aperture to f/8, which is two stops up from f/16. So that means we need to stop down the shutter speed two stops to get the correct exposure. The reason we have to do this is because you are letting more light into the camera at f/8 compared to f/16. So to compensate, you need a shutter speed that let's in less light. So that means on a sunny day with an aperture of f/8 and an ISO of 400, we need to set the shutter speed to 1/2000th.
And of course this works in reverse. Again, its a sunny day, and ISO is 400 and you know you want to shoot with a shutter speed of 1/1000th. So what aperture should you dial in? We know to get proper exposure on a sunny day with an aperture of f/16 and ISO of 400, we need a shutter speed of 1/400th (or 1/500th). So if we want a shutter speed of 1/1000th, which is one stop up, that means we need an aperture that is one stop down, in this case, f/11.