Understanding Light and Aperture
We need exposure in order to take photos. Exposure is defined as the total amount of light allowed to fall on film or image sensors. How do we control that total amount of light? Well, exposure is a combination of shutter speed (the amount of time the film or image sensors are hit with light) and the amount of light that passes through the lens. The light passing through the lens is controlled by the aperture.
What Is Aperture?
The aperture on your camera is a hole between the lens and photographic medium that light passes through. The wider the hole, the more light travels through. We need to control the aperture because lighting conditions are always different. A room at night has a lot less light than an exterior shoot on a bright and sunny day. You would shoot the room with a open aperture and the day shots with a closed one.
Aperture openings are measured in f-stops. Typically, the scale on your camera ranges from f/1.4 to f/16, with the lower number being the widest. F numbers are determined by divided the focal length of your lens by diameter of your aperture. This is a calculation that you'll most likely never have to do because your camera does the work for you. All you need to do is select an f-stop from your menu.
Controlling the Aperture
When you're shooting outdoors during the day, your aperture is going to be dependent on the sun, otherwise you'll have an overexposed or underexposed image. You can use lights and reflectors to help manipulate the lighting, but the sun is your main source and that makes it the boss.
Shooting in a studio is different though. Here, you have control. You can set your key light, choose an f/stop and go on working from there. If the image is too dark, you can just add lights, and if it's too bright, you can take some away. Part of your job as a photographer is to keep the exposures balanced and the studio is where you have the most control to get it done without changing the aperture.
Exposure is dependent on the relationship between aperture and
shutter speed. If the shutter speed is changed and it is faster than
before, you need to compensate for that lost exposure time by opening
your aperture and allow more light to pass through. Likewise, if the
shutter speed is slowed, then you need to close the aperture or your
photos will be overexposed.
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