2012年10月16日星期二

Good Way to Understand Aperture

Aperture is one of the three pillars of photography, the other two being ISO and Shutter Speed. Without a doubt, it is the most talked about subject, because aperture either adds a dimension to a photograph by blurring the background, or magically brings everything in focus.

1) What is Aperture?
Aperture is a hole within a lens, through which light travels into the camera body. Take our eyes as example. The cornea in our eyes is like the front element of a lens – it gathers all external light, then bends it and passes it to the iris. Depending on the amount of light, the iris can either expand or shrink, controlling the size of the pupil, which is a hole that lets the light pass further into the eye. The pupil is essentially what we refer to as aperture in photography. The amount of light that enters the retina (which works just like the camera sensor), is limited to the size of the pupil – the larger the pupil, the more light enters the retina.

2) Size of Aperture – Large vs Small Aperture
In photography, aperture is expressed in f-numbers (for example f/5.6). These f-numbers that are known as “f-stops” are a way of describing the size of the aperture, or how open or closed the aperture is. A smaller f-stop means a larger aperture, while a larger f-stop means a smaller aperture. Most people find this awkward, since we are used to having larger numbers represent larger values, but not in this case. For example, f/1.4 is larger than f/2.0.
Take a look at this chart: The larger the f-number, the smaller the aperture.

3) What is Depth of Field?
The size of the aperture has a direct impact on the depth of field, which is the area of the image that appears sharp. A large f-number such as f/32, (which means a smaller aperture) will bring all foreground and background objects in focus, while a small f-number such as f/1.4 will isolate the foreground from the background by making the foreground objects sharp and the background blurry.