Controlling Exposure with a Canon EOS Rebel T3 Series Camera
Any photograph, whether taken with a film or digital camera, is created by focusing light through a lens onto a light-sensitive recording medium. In a digital camera like the Canon Rebel T3 or T3i, it’s the image sensor, which is an array of light-responsive computer chips.
Between the lens and the sensor are two barriers, the aperture and shutter, which together control how much light makes its way to the sensor. The actual design and arrangement of the aperture, shutter, and sensor vary depending on the camera.
When you press the shutter button halfway on your T3 or T3i, the current f-stop, shutter speed, and ISO speed appear in the viewfinder display. Or if you’re looking at the Shooting Settings display, the settings appear as shown. In Live View mode, the exposure data appears at the bottom of the monitor and takes a form similar to what you see in the viewfinder.
In the viewfinder and on the monitor in Live View mode, shutter speeds are presented as whole numbers, even if the shutter speed is set to a fraction of a second. For example, for a shutter speed of 1/1000 second, you see just the number 1000 in the display. When the shutter speed slows to 1 second or more, you see quote marks after the number in both displays; 1 indicates a shutter speed of 1 second, 4 means 4 seconds, and so on.
The viewfinder, Shooting Settings display, and Live View display also offer an exposure meter. This little graphic serves two different purposes, depending on which of the advanced exposure modes you’re using:
In manual exposure (M) mode, the meter acts in its traditional role, which is to indicate whether your settings will properly expose the image. When the exposure indicator (the bar under the meter) aligns with the center point of the meter the current settings will produce a proper exposure. If the indicator moves to the left of center, toward the minus side of the scale, the camera is alerting you that the image will be underexposed. If the indicator moves to the right of center, the image will be overexposed.
In the other modes (P, Tv, Av, and A-DEP), the meter displays the current Exposure Compensation setting. Remember, in those modes the camera sets either the shutter speed or aperture, or both, to produce a good exposure. Because you don’t need the meter to tell you whether exposure is okay, the meter instead indicates whether you enabled Exposure Compensation, a feature that forces a brighter or darker exposure than the camera thinks is appropriate. When the exposure indicator is at 0, no compensation is being applied. If the indicator is to the right of 0, you applied compensation to produce a brighter image; when the indicator is to the left, you asked for a darker photo.