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Aperture is one of the most confusing aspects of photography for new photographers (and some old hands). In truth, it does not have to be confusing. The aperture is an adjustable opening inside the camera lens that works very similar the iris in your eye.
When the aperture opens wide (like your eye dilating), more light is allowed through the lens to expose the film. When the aperture is narrow (like your pupil in bright light), less light reaches the film. This works in conjunction with shutter... speed and film speed to determine the total amount of light that reaches the film. Aperture size also affects depth of field.Continue to 2 of 4 below.
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Aperture is measured using F-Stops. F-Stop numbers represent a fractional formula representation of the amount of light allowed to pass through the aperture. In simpler terms, F-Stop numbers get bigger as the aperture gets smaller, just like shutter speed numbers get bigger as the time the shutter is open gets smaller. Each increasing F-Stop number roughly represents a halving of the light reaching the film. As the aperture closes, more of a scene will come into focus as well (as we learned in... the depth of field lesson).
F-Stop Relationship to Light and Depth of Field
- Big F-Stop Number = More Light Needed = Larger Depth of Field
- Little F-Stop Number = Less Light Needed = Less Depth of Field
Many photography texts over the years have attempted to drill the idea of small aperture = large F-Stop into new photographers' brains. While this is important to know, I have seen far too many new photographers become discouraged trying to remember this inverse relationship in the field. If it is easier for you to remember the F-Stop relationship to light and depth of field then by all means, use the memory method that works best for you in the field. If you miss a shot because you are trying to remember the aperture to F-Stop mechanics then it is just a hindrance.
While there is actually a huge range of F-Stops (aperture sizes) possible, depending on your lens, there is a common ground middle range that most consumer lenses are capable of operating within.
Common F-Stop Values
Continue to 3 of 4 below.
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Aperture is set on cameras by turning a specified dial on the camera body. In older, fully manual cameras, this is a dial on the camera lens that is marked with F-Stop numbers. In newer cameras, the aperture is generally displayed on an LCD screen while the photographer turns a small wheel near the shutter release button to adjust the setting. The exact placement of the wheel will vary from camera to camera. On point and shoot cameras, there may not be a control to select specific aperture or... F-Stops.
If your camera does not have a way to manually set the aperture you may need to understand your camera's preprogrammed modes to obtain the desired aperture. Many SLR cameras also have these preprogrammed modes as well as a few additional modes of fine control.
Some Examples of Aperture-Specific Preset Camera Modes
Aperture Priority - Allows you to set the aperture and the camera determines shutter speed and ISO
Landscape Preset - Uses a small aperture (large F-Stop) by default
Portrait Preset - Uses a large aperture (small F-Stop) and slow film speed by defaultContinue to 4 of 4 below.
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Aperture in Preset Camera Modes
Almost all automatic cameras today have some sort of preset shooting modes. These are designed for specific situations such as action, landscapes, and portraits. If you know what these modes change about your camera settings you can use them to your advantage in many more situations than just the intended ones. We've covered a few modes that are heavily weighted to aperture but now let's find out how aperture works in more preset camera modes.
How Aperture Works in Preset Modes
Macro... mode is an automatic setting mode where the camera is predisposed to use the large aperture to compensate for the DOF compression of close-up shooting. In this mode, you can not set the exact aperture you want but you can lessen your chances of an out of focus close-up subject by using this mode.
Landscape mode is basically a large DOF mode. Landscape is programmed to give the smallest aperture (largest F-Stop) possible in order to ensure a large depth of field. This means that the shutter speed will be slower. If your camera does not allow Manual or Av mode and you are wanting to shoot a subject where the background is in focus, try the Landscape setting.
Portrait mode uses a large aperture to create a small DOF. Portrait is programmed to have a shallow depth of field (large aperture/small F-Stop) and use a slow film speed in order to throw the background out of focus and obtain a very fine film grain. Use this setting anytime you want a blurry background.
Manual setting is marked "M" on newer cameras and is, in effect, the only setting on manual cameras. Manual mode means that you are fully in charge of the settings of your camera. If you set the aperture/F-Stop while in M mode, you will need to make an adjustment to shutter speed yourself in order to maintain a correct exposure. Use your camera's light meter to ensure the values are in balance.
The setting on your camera marked "Av" is called Aperture Priority mode. This means that if you use Av mode and set the aperture/F-Stop, the camera will adjust your shutter speed value to maintain a correct exposure.
Program mode is marked by a "P" on the few cameras that have this option. In program mode, your camera responds to some preset conditions you programmed through the menu. Generally, this mode allows you to set either the shutter speed or the aperture while the camera adjusts the other setting to maintain proper exposure.