Now we’ll learn how to take off the training wheels and take a little control in lighting our photos. We’ll take what our camera automatically calculates as the “right” exposure and then dial it down – or up. This is sometimes referred to as exposure compensation or exposure bias.
So this is how my camera automatically exposes this particular scene:
We’ll call this 0. As in, it has an exposure value of 0. Or, if you’re into the brevity thing, 0 EV. Exposure value should be considered a relative value; each camera may judge perceive 0 EV to be a different amount of light.
What’s important to us is to see 0 as just a starting point.
If I increase EV to 1, I am doubling the amount of light in the scene, which looks like this:
If I increase the EV to 2, I am doubling the light that was at EV 1. Which, if you remember multiplication, will be 4 times the light at EV 0:
If we dial back down to EV 0 and then to EV -1, we’ll have half the light of the default exposure:
And then EV -2 will be one-fourth the light of EV 0:
If that math was too difficult for you, it’s OK (…but sad). It’s only important to understand how EV relates to a relative increasing or decreasing of light for a particular scene.
Some quick vocabulary: A change in EV of 1 is also referred to as a stop of light. Hence, EV +1 can also be read as “increase the light by one stop.” Likewise, EV -2 is “losing two stops of light.”
I’m a physics major and am comfortable with math. Exactly how much light is in that scene?
That’s a measurement not worth figuring out for this lesson (if ever). You make adjustments based on whether you think a scene needs more or less light, not to get a certain amount of photons onto the camera sensor.
In order to add or subtract light from the scene, your camera will adjust the relavant settings by relative amounts. Did you want double the light in the scene (+1 EV)? Then your camera may double the length of the shutter speed.
In later chapters, we’ll adjust shutter speed and other factors to achieve changes in exposure value. For now, we leave those adjustments to the camera’s computer, leaving us to think only about exposure value.
This camera mode is called Program mode.
How do I turn on Program mode?
Most cameras have something called Program mode, usually listed as P on a dial or menu setting.
Here’s the P mode on the Nikon D80 dial:
After you’ve figured out how to go into Program mode, you need to find the actual button/dial/control that increases and decreases the exposure. This varies with each camera but it should be a prominent physical button(s) or dial. Consult your instruction manual if you need help.
For point-and-shoot cameras: the exposure control is usually buried in the camera’s menu system. Look for the
+/- menu item. It will look something like this (from the Nikon COOLPIX S200):
On a DSLR-like camera: there will usually be a dial or physical button dedicated to EV control. The Canon 40D (and similar bodies) have a configurable main dial on their backs:
I’m in ‘Program’ mode and found the EV dial. Now what?
First, look at whatever your camera has for a “viewfinder”: either an actual viewfinder or an LCD screen on the back.
There should be a line with ticks, starting from -2 to 0 to +2 (remember our discussion about EV?). Each number on that axis refers to a doubling or halving of light from adjacent numbers.
Play around with the control. Pushing/spinning it one direction should move the tick mark in one direction or the other.
Let’s test it out:
1. Point your camera at a well-lit daylight scene.
Without doing anything, your camera should calculate an exposure for the scene. Dark areas will be in total shadow. Details in the lightest areas will be “blown out.”
2. Change the exposure setting to -2
The overall scene should darken. Your camera is now exposing for the highlights, letting you see detail in the lightest areas while blacking out the details in the relatively darker areas.
3. Change the exposure setting to +2
The overall scene should lighten. Your camera is now exposing for the shadows, letting you see detail in the darkest areas at the expense of blowing out the detail in all of the relatively lighter areas.
When would I want to manually adjust exposure?
Anytime you want more shadows (underexposure) or highlights (overexposure). This is not something the camera can decide for you automatically, which is why we take a little control with Program mode.
In Program mode, I changed the EV to +2 and now my photos are blurry. What gives?
You’ll quickly find that as with most things in the universe, nothing comes for free. By going to +2 EV, you were telling the camera to quadruple the light for the photo. The camera responded by slowing the shutter speed long enough to let four times as much light in. And, as we’ll learn in the shutter speed chapter, this can cause objects to go blurry.
We have the option of also managing shutter speed. But before we start multi-tasking, let’s practice adjusting the exposure value in Program mode.