If you've ever picked up a camera, the answer is bound to be "yes". Fortunately, you don't always have to be surprised by what your camera decides to do if you learn a little about exposure and how to control it.
Without being too technical, "exposure" is the general term for the overall lightness or darkness of an image. An "over-exposed" image is too bright, and an "under-exposed" image may appear too dark. Although exposure is somewhat subjective, and can depend on your creative intent, most people generally agree on what is a properly vs. improperly exposed image.
So what determines how bright or dark an image is? There are three camera settings that control exposure: aperture, shutter speed, and sensitivity (a.k.a. ISO).
The first two settings, aperture and shutter speed, determine how much light reaches the digital sensor (or film) inside the camera. Aperture refers to the size of the opening inside the lens that light can pass through. The larger the opening, the more light that can pass through in a given amount of time. The more light, the brighter the image.
Shutter speed refers to how long the sensor (or film) is allowed to be exposed to the light coming through the lens. The shutter normally keeps the sensor covered, opens briefly when you take a picture, and closes immediately afterward. The slower the shutter speed, the longer the sensor is exposed, and the more light hits the sensor. Once again, the more light, the brighter the image.
Sensitivity, or more commonly, ISO, determines how the digital sensor responds to the light that hits it. The higher the ISO setting, the more sensitive the camera's sensor becomes, and the brighter the image will be. For digital, the sensitivity of the camera's sensor is a setting that can be changed at anytime. For film however, the ISO is a property of the roll of film itself, and cannot be changed, except by changing to a different type of film.
This is a basic explanation of exposure. The main point is that it is possible to control how bright or dark your images are, and that there are only three settings that affect this. Next we will look into these settings in more detail and talk about how you can use this knowledge to get the photos you envision in your mind's eye to actually show up on the back of your camera!
