Aperture in Photography
Last week I discussed Shutter Speed as one of three factors to control exposure. For this week’s new series of articles I am going to cover the basics of Aperture.
What is Aperture?
Let’s take a look at a definition of aperture from Wikipedia:
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at the image plane. If an aperture is narrow, then highly collimated rays are admitted, resulting in a sharp focus at the image plane. If an aperture is wide, then uncollimated rays are admitted, resulting in a sharp focus only for rays with a certain focal length. This means that a wide aperture results in an image that is sharp around what the lens is focusing on. The aperture also determines how many of the incoming rays are actually admitted and thus how much light reaches the image plane (the narrower the aperture, the darker the image for a given exposure time). In the human eye, the pupil is the aperture.
An optical system typically has many openings, or structures that limit the ray bundles (ray bundles are also known as pencils of light). These structures may be the edge of a lens or mirror, or a ring or other fixture that holds an optical element in place, or may be a special element such as a diaphragm placed in the optical path to limit the light admitted by the system. In general, these structures are called stops, and the aperture stop is the stop that determines the ray cone angle, or equivalently the brightness, at an image point. In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the physical stop or the opening itself.
Sounds pretty complicated, right? But stay with me! In this series of articles I am going to cover the practical uses of aperture in photography rather than the scientific explanations. In general terms, and for all types of photography, the aperture is the unit of measurement that defines the size of the opening in the lens, which can be adjusted to control the amount of light reaching the film or digital sensor. The size of the aperture is measured in f-stops.
In its most basic role the aperture controls the volume of light passing through the lens. As you can see in the above diagram, the lower the number (f-stop) the larger opening, which allows more light to pass through; the higher the f-stop, the narrower the opening, with less light coming through the lens.
How/where do I change the Aperture setting?
In modern digital cameras, you can control the aperture’s f-stops through camera body. If you set your camera to Aperture Priority (A, or AV), you set the f-stop by using the main command dial and the camera will then select the correct shutter speed and/or ISO to adjust the exposure.
In these photos I used different f-stops (high number/narrow opening and low number/wide opening); because I was in Aperture priority mode the camera adjusted the exposure by changing the shutter speed.
This concludes the basic look at what aperture is and does. Stay tuned for Part 2 where we’ll look at some creative uses for aperture settings.
Ted and the Omnilargess Team