There are three controls or settings on the camera that affect the exposure:
1) aperture; 2) shutter speed ; 3) ISO
So, how do we choose what settings to use?
First off, it is important to understand there is more than one correct setting to properly expose the scene. These are called equivalent exposures.
But you need to start somewhere. And that starting point is really simple. And it has been around for a long time. It’s called the Sunny 16 rule … or Basic Daylight Exposure.
For those of you that were film shooters, remember the little writing that was on the inside of the film box? Well, that was the Sunny 16 rule. And it’s guaranteed to work every time.
The rule is very simple:
1) It’s not sunrise or sunset, as the sun must be 15-degrees above the horizon and your subject is lit by full sun, meaning not back-lit or in the shadows or it is cloudy outside.
2) Set your lens aperture for f/16
3) Whatever your ISO setting is currently at, take that number and make it your shutter speed as well. So if your ISO is at 200, then make your shutter speed be 1/200th of a second, while at f/16.
4) Take the picture, as it is perfectly exposed.
If your ISO is at 400, then your exposure would be 1/400th of a second at f/16.
If your ISO is at 640, then your exposure would be 1/640th of a second at f/16.
Why does this work? Well, it’s all about the laws of physics and the light from the sun being constant. It’s guaranteed to work every time.
But remember, your subject (what you are shooting) is lit by full sun. This rule doesn’t work if it is cloudy or you are shooting in the shadows.
It is important to know that once you get your Sunny 16/Basic Daylight Exposure, that is just your starting point. From there, you can calculate an equivalent exposure, changing your f-stop or shutter speed, to achieve a certain depth of field or specific motion blur or stop-action. We’ll talk about calculating equivalent exposures in the next episode.