Photography 101 — The Photographic Triangle: Aperture (1 of 4)

by Richard on June 14, 2010 · 0 comments

As a photographer, understanding light is the most important and the most difficult thing to master. To truly master light takes a substantial amount of time and is out of the scope of this article but these articles will provide a basic understanding that will help you take much better photographs.

A camera is nothing more than a light sealed box with an opening at one end and some sort of light sensitive medium at the other end. Exposure is the total amount of light allowed to fall on the photographic medium during the process of taking a photograph. There are three basic parts to a proper exposure: aperture, exposure time and ISO, or film speed. This is commonly referred to as the Photographic Triangle. In this 4 part article I try to explain what each means and how all three relate to each other when taking a photograph.

Aperture

An aperture is a hole or an opening through which light travels to reach the photographic medium. The wider the diameter of the hole the greater the amount of light that is allowed to enter. It is normally notated as f/# and called an f/stop. The f/stop is the ratio of the focal length of the camera and the diameter of the opening.

The normal f/stops are measured logarithmically as f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22… and so on. The lower the number the bigger the diameter of the opening (see chart). Each stop doubles, or halves, the amount of light that passes through the aperture.

The key thing to remember is that this is controlled by the lens not the camera. If you want to shoot fast, or wide open, you will need to consider this when purchasing lenses. Fast lenses can get pretty pricey since a larger aperture stop requires larger diameter optics, which are heavier and more expensive.

There is a trade off in adjusting the size of the aperture. Smaller stops (larger f numbers) produce a longer depth of field, allowing objects at a wide range of distances to all be in focus at the same time. Subsequently, larger stops (smaller f numbers) produce a very small depth of field. The photos below show the same object photographed at an f/stop of f/1.8 and f/16:

shot at: f/1.8, exp 1/1600, ISO 100

Shot at: f/14, exp 1/25, ISO 100

Notice the shallow depth of field in the first photo. This can be useful for using in creative portraits or bokeh shots but would not be the best for a wide angled landscape shots.

Another Trade off comes if you own a zoom lens. Most low cost zoom lenses usually have a maximum f/stop of f/3.5 and most point and shoots have a max aperture of f/2.8. Also due to the limitation of the optics it is rare that a low cost lens will be able to stay at a fast aperture as you zoom the lens.

One good way to play with and learn how your current equipment handles aperture is to set your camera to the Aperture Priority, or the AV setting. This allows you to set the aperture and sometimes the ISO settings to what you want and the camera sets the exposure time based off the light meter reading.

In part two we will cover ISO or film speed.

*This is part of my series to introduce people to the world of photography. My hope is to help current DLSR camera owners to stop relying on the auto setting of their camera and unlocking the photographic potential of what they hold in their hand.

Richard Call is a Nashville, Tennessee based photographer whose work has been published locally as well as internationally and can be seen at richardcallphotography.com

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