Aperture of a lens

Lens Aperture Definition

Specifically, the term “aperture” refers to an opening (or hole). In photography, the lens aperture is the opening in the lens through which light will pass. The size of aperture in a lens can usually be controlled by adjusting a very thin set of blades within the lens assembly which is often referred to as the diafragm.

Most point and shoot camera’s have settings for different scenes. By changing the scene selection (or scene mode) the lens aperture is usually adjusted automatically. More complex camera’s such as (D)SLR cameras allow the photographer to adjust the size of the lens aperture manually. This provides more artistic control over the resultant photographs.

Measurement

The size of the aperture in photography is commonly referred to as the f-number or f-stop. As the f-number is adjusted higher, the size of the aperture gets smaller letting in less and less light. The reverse is also true. As the f-number is adjusted lower, the opening in the lens gets bigger giving us a large aperture. More light is then allowed into the camera.

The f-numbers are measured on a scale of “stops”. Each full stop represents twice the value of the previous. This means that when adjusting the f-number down, the opening in the lens will be double the size for each stop. When adjusting the f-number up, the opening in the lens will halve in size for each stop.

Effects

OK, so now we know what aperture is and how it’s measured. But how can we use it and what changes visually by using aperture?

Well firstly, by making the opening in the lens bigger or smaller, we are controlling how much light enters the camera. This will, in turn affect the exposure of the shot. In reality, aperture can’t be used alone. Your shutter speed must always be adjusted too. Lighting and artistic intentions aside, generally speaking, we use a faster shutter speed for low f-numbers, and a slower shutter speed for high f-numbers.

Personally, I feel the most interesting effect of aperture is how it effects focus in a photo. Generally speaking, a high f-number will result in just about everything in our frame being in focus. High f-numbers are used for long shots such as in landscape photography where the photographer is aiming for the entire scene to be within focus. In contrast, low f-numbers will reduce the area of focus within your frame so that the subject remains in focus, but everything in the foreground and background becomes blury. These effects, which in reality result from more than just the camera aperture setting, are collectively referred to as Depth of Field (DoF), which I’ll be writing about in another post.

For more detiled information about lens aperture, check out Wikipedia.

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