Now that you understand the settings of both shutter control and aperture settings you need to know what influence they have on overall exposure. Many of you are probably familiar with overexposed and underexposed pictures. Overexposed pictures are a result of too much light coming through, and underexposed pictures are those which are too dark.
Let's say for example, that we used a fast shutter speed (to limit the amount of light coming in) and a high aperture number (small home) to limit the amount of lighting coming in and to capture the greatest detail for a landscape photograph. The following would be the result.
Notice how in this photograph the subject is underexposed. There is not enough light shed on the film (or CCD if the camera was digital) to bring out the details of the subject. In the case above it may have been the intention of the photographer to create a darker image and often underexposed images are taken intentionally. Your concern is to ensure you don't take unintentional underexposed images.
Now image you set your aperture setting to a low number (larger opening to let in more light) and you set your shutter speed to a longer exposure time. The result would be a photograph which overexposes your photograph. Look at the following example.
Therefore it is important to know how shutter speed and aperture work in conjunction with each other to determine the overall exposure levels of a photograph. Think of shutter speed and aperture as a teeter totter. On one side you have aperture and on the other side you have the shutter speed. As the shutter speed gets set to one increment higher the aperture setting needs to get set to one increment lower in order to keep the light coming into the camera the same.
Source: Apogee Photo
And don't forget that every decrease in shutter speed decreases the amount of light be half and every increment the aperture opens doubles the amount of light coming in. You can therefore use different combinations of aperture settings and shutter speed settings to achieve the exact same exposure levels. Look at the chart below to learn more about how to balance aperture settings with shutter speed settings.
Since shutter speed and aperture settings move in equal increments, you can trade shutter stops for aperture stops and have the same exposure. This gives you a range of aperture openings and shutter speeds that you can use.