In a previous episode, we explained the three things affecting exposure are:
1) aperture; 2) shutter speed; and 3) ISO.
And to establish your exposure, you use the Sunny 16/Basic Daylight Exposure rule. Set your f-stop at f/16, and and then simply matching your shutter speed to your ISO number. For example, f/16 with an ISO of 200, so your shutter speed is 1/200th of a second.
And if you need to adjust your exposure to have a certain aperture, shutter speed or ISO, you need to compensate by creating an equivalent exposure. When you adjust f-stop, shutter or ISO, the scale tips on the exposure and you have to adjust one of the other two to bring your exposure back to “normal”. That’s equivalent exposure.
All of these technical settings will give you a properly exposed photographed of a sunlit scene.
But sometimes technically correct isn’t part of your artistic vision, or how you see the scene.
You might want to underexpose the scene to create deeper shadows.
You might want a longer exposure to allow for motion blur.
You might want to overexpose the scene to create a “higher key” photo.
You might want to add filters to the scene.
In each of these examples, you need to start with the BDE/Sunny 16 exposure, then calculate how much of an exposure change you need, opening up or closing down one of the three controls, in order to achieve the desired effect.
With filters, there is a level of exactness in how much you need to open up your exposure (letting in more light) as all filters have a specific number of stops that you need to compensate for the reduced light the filter blocks.
For example, a polarizing filter reduces the light passing through the lens, so one of the three controls needs to be adjusted to allow in more light. A polarizing filter typically blocks between 2 to 3 stops of light, depending on the manufacturer. We’ll show you how to calculate the exact amount of compensation for polarizing and other modifying filters in an upcoming episode.
But here’s a filter tip: when you use a graduated neutral density filter, which applies a gradual darkening of the scene, typically used to darken skies, you don’t need any exposure compensation for the filter. The subject of the scene, what you are exposing for, is unaffected by the filter. All you are doing is letting the filter darken the sky, which is the objective of these filters. Just drop it into place and let it do its job!
We’ll talk more about filters in an upcoming episode. But remember, regardless of the changes through filtration or exposure adjustments, you control how the final photograph will look. That’s your artistic vision, not the cameras’.
A technically correct picture isn’t always a visually dynamic photograph. That’s where your artistic intent comes into play.