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Aperture

Camera Aperture is quite simply a hole. It is an adjustable hole. The adjustments are normally 1 stop increments. For example f/2.8 is double the size of f/5.6. Because the aperture is double the size, it lets twice as much light onto the sensor. This can result in a brighter image (1 stop brighter) or a faster shutter speed to achieve the same brightness. The shutter speed would be twice as fast (1 stop) in this case.

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By CelinaTH – Own work, CC BY-SA 3.0, Link
Reducing aperture: The diagram shows apertures from f/2.8 on the left to f/22 on the right.

Large apertures

Why would I pick f/2.8 over f/5.6?

Choosing f/2.8 will help you in a low light situation when you have to hold the camera by hand. The shutter will be twice as fast as the f/5.6.

Cat portrait shallow DOF

Cat portrait at f/2.8 creating a shallow DOF

For a more advanced discussion see my Arguing for Aperture article.

Depth of field illustration.svg


By Diaphragm.svg:
derivative work: BenFrantzDale (talk) – Diaphragm.svg, CC BY-SA 3.0, Link

Aperture’s effect on blur and DOF. The lens is focused on point 2 creating a sharp point on the sensor (5), but the objects not in the focused plane (1 and 3) are blurred, (circles of confusion). Decreasing the aperture size (bottom diagram) reduces the size of the blur for objects at different distances. When the blurring is imperceptible, all points are within the Depth of Field (DOF).

Aperture choice can be useful to manipulate the shutter speed. Aperture works with ISO and shutter speed to form the exposure triangle. But really your choice of aperture should be a consideration of DOF. DOF is an important key to communicating Depth and for guiding attention through an image.

But… aperture is not the only choice that affects DOF. Focal length (how wide is your lens) affects aperture. A wide angle lens will naturally have a large DOF whereas a long lens will naturally have a shallow DOF. Technically, DOF is the same in both, but it is the distance of the lens to the subject that will contribute to the shape of the DOF.

Ice on the beach at Jökulsárlón, Iceland.

Ice on the beach at Jökulsárlón, Iceland. Aperture f/6.3 for fantastic sharpness in the subject and no need for super sharp background.

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