The Canon EOS Digital Rebel T1i/500D Companion
The Canon EOS Digital Rebel T1i/500D Companionserves as a full-on photography class, one that covers everything, including technical matters and exposure theory, composition theory, and how to find images and expand your visual sense. However, unlike a regular photography class, the lessons in this book are built specifically around the T1i. That means every concept is presented in terms of the T1i/500D's controls and features. So, by the time you're done with this book, you'll be a better photographer, whether you're shooting simple snapshots or aiming for something more.Tips for Using Exposure Compensation to Over- or UnderexposeBy Ben LongThese days, almost all cameras have an Exposure Compensation control, which simply lets you make a relative exposure change. That is, you can tell the camera, "I don't care how you metered the scene; I just want you to go up from there by one stop."Try using exposure compensation now:1. Frame a shot.2. Press the shutter button down halfway to meter your scene (the camera will also autofocus and take a white balance reading).3. After the camera beeps, the viewfinder and status LCD will show you the shutter speed and aperture settings that it has calculated.4. Take the shot.5. Now frame the same shot, and again press the shutter button halfway down to meter the scene.6. Using your thumb, press the Exposure Compensation button on the back of the camera.Dial in a specific amount of over- or underexposure.7. Rotate the Main dial until the Exposure Compensation display in the view- finder indicates a one-stop overexposure. (If you haven't changed the camera's defaults, then this will be three clicks on the dial.)8. Take the shot.The Exposure Compensation display highlights. Turn the Main dial to increase (brighten) or decrease (darken) the setting.Food For Thought: What's Wrong With Over- or Underexposing?Of course, once you start tinkering with the camera's carefully concocted exposure settings, you run the risk of over- or underexposing your scene to the point where bright things blow out to complete white or where dark shadows fall to complete black. When an area in your image goes to all white or all black, it becomes an area with no detail. Detail in a photo is constructed from contrasting tones, and when part of an image is one color, it looks like a flat surface.In the case of shadows, this isn't so bad. A black shadow simply looks like an area that's too dark to see. Unless there's some detail in the shadowy area that you really want to keep visible, letting a shadow darken is not too terrible. Overexposed highlights, though, are almost always distracting. An area of complete white acts like a magnet for the viewer's eye and can sometimes upstage your subject.However, at times it's worth overexposing a highlight to get better tonality on your subject. Also, a little bit of overexposed bright spots—small bits of chrome on a car, for example—won't necessarily be noticeable. While there are no hard and fast rules about how much over- or underexposure is too much (and many times, overexposing an image can be an effective stylistic choice), it's important to understand the risk and make an intelligent decision.Now go into playback mode and look at the two images. The second one should be much brighter than the first one. This is the image that was over exposed. Note that you didn't tell the camera a specific shutter speed or aperture. Instead, you simply told it to go up one stop from whatever it thought was the correct exposure. The T1i has an exposure compensation range of -2 stops to +2 stops. By default, the control moves in 1/3-stop increments.When you use exposure compensation, you don't actually know exactly how the camera will achieve its over- or underexposure, but the camera does follow a predictable method. It will always try to achieve its change in a way that doesn't involve a shutter speed that might be too slow for handheld use.Remember, a slower shutter speed means that the shutter is open longer, which means that your images are more susceptible to the blurring and softening caused by shakiness in your hand. If you have the ISO set to Auto, the T1i will often effect the change by altering the ISO setting, but it will never do this to the point of introducing noise into your image. Because there's no visible difference between ISO 100 and 400, the T1i has two stops of ISO latitude to play with, meaning it will often keep the shutter speed and aperture the same as you change exposure compensation.