Exposure is the amount of light that your camera uses to produce a photo. The entirety of this book is pretty much devoted to how to control exposure by changing how your camera lets light in.
Sometimes you just have to make do with what light you have. Without knowing anything about manual controls, you can still move around and move your subject. Knowing manual controls gives you many more options and flexibility.
For our purposes, the complicated math formula behind this can be reduced to:
- More light == brighter photo
- Less light == darker photo
How does a camera automatically determine the proper exposure?
When turned on and pointed at a subject, your camera is taking in light. It then calculates how much light is needed to keep the subject (or the entire scene) from being too dark or too bright.
Try this.
- Point your digital camera at a dark place, such as a corner or under the table.
- Then point it quickly at a bright scene, such as out the window. The camera’s LCD should turn almost completely white.
The following photo is taken from inside of Federal Hall on Wall Street, right after I had pointed it toward a dark corner:
- After a second or two, the LCD screen should darken a bit overall, revealing more detail in the scene:
This delayed reaction is caused by the lag in calculating the correct exposure. Your camera’s computer is trying to figure out the right amount of light to let in.
How much is the right amount of light?
The long answer: Figuring that out is the basis of this entire book, and the “right” amount varies per situation, subject, and photographer’s aesthetic sensibility.
The answer, for now: It’s what your computer determines is the right amount of light to properly show the subject.
In the graphic below are three iPhone photos of the same scene. The orange circles represent the areas that the phone camera is exposing for (you’ll learn how to do this in the spot-selection lesson):
In each frame, the camera attempts to make the area within the orange circle appear as a neutral midtone. Everything else in the photo has a brightness level relative to the exposed spot.
How does the camera know what the “subject” is?
By default, most cameras assume that it’s what the center is. In simple point and shoots, you can’t change this. In modern phone cameras, you have some flexibility in choosing the spot to expose, which I cover in the spot-selection lesson.
The default settings for most cameras, though, judge the light from multiple regions (and each camera may have a different mix). In the photo below, I’ve let my camera pick what it considers the proper exposure (an exposure value of 0, as I explain in a later chapter):
The camera’s sensor is getting a lot of light from the overcast sky and adjusts its settings so that details in the sky, such as the cloud in the top right, can be seen. Unfortunately, that ends up obscuring the details of the painter, who is dark in comparison to the sky.
Below, I’ve made a manual adjustment by telling the camera to increase its exposure +1.3 steps (or “stops”). This effectively increases the amount of light taken in by the camera by about 2.5 times as much as 0 EV.
But don’t worry about the numbers. It’s just important to see that the scene is significantly brighter than it was in the previous version. The sky is basically white, but you can now make out the details in the painter:
This isn’t a great photo op either way (and would look better with some post-processing work), but the bottom option with the increased exposure value is closer to how I want to capture the scene: the painter, not the sky, is the interesting part.
My eyes can see both clouds and details in the shadows, why can’t my camera?
This has to do with dynamic range: your eyes can see a greater range of light than the best camera. More expensive cameras have a higher dynamic range than cheaper ones. But the camera will always capture less detail than what you remember seeing.
What’s wrong with letting the camera properly expose the scene?
It’s not about right or wrong; it’s about what visual effect you intend to show.
In the last chapter, we learned how the sun behind the subject creates a silhouette.
When a camera is in auto-exposure mode, it will adjust the light so that your subject is not a silhouette.
As the subject gets brighter, so does the rest of the background. This is what is called, “blowing out the background.”
In the photo below, I deliberately reduced the exposure to use one-fourth the light compared to the camera’s default exposure. The model is almost completely a shadow. Had I let the camera do the exposure, the details in the model’s clothing could probably be seen, but the entire sky would likely be white, i.e. blown out.
In other words, the “well-exposed” photo is not always the best photo.
The camera generally does a great job when the light is right.
But under extreme conditions, such as bright sunlight on a snowfield. Or a dark room. Or for if a ray of light happens to shine directly into the region (generally, the center point) where the camera makes its judgment, the camera may do something you don’t want.
This is why we want to take control of exposure for ourselves.
