It is July and the dog days of summer are upon us. What better time to sit back, get a cool drink and revisit some of the basics of photography. This is the first post in a 5 part series on photography fundamentals called Photography 101. Over the next five weeks, we will cover:

  1. The exposure triangle
  2. Rule of thirds
  3. Depth of field
  4. Lighting basics
  5. Composing a shot

Let’s jump in and get started.

The exposure triangle is a simple graphic depiction of the three elements one needs to consider when trying to get a properly exposed shot. It consists of three interconnected parts: aperture, shutter speed and ISO. Each of these is defined below.

Exposure Triangle

Aperture: an adjustable opening in a lens through which light travels. The size of this opening is called the f-stop. Aperture is used to control how much light enters into the camera. The smaller the number (e.g. f2.8), the bigger the opening and the more light is allowed into the camera. A setting of f2.8 lets in more light into the lens than a setting of f11. Aperture plays a key part in manipulating depth of field.

Shutter speed: the second element in the exposure triangle is shutter speed. This is the amount of time that the shutter is open. Along with aperture, shutter speed allows us to control the amount of light entering the camera. Slower (longer) shutter speeds let in more light and faster (shorter) shutter speeds allow in less light. Shutter speeds are measured in fractions of seconds e.g. 1/60 of a second or 1/4000 of a second. Shutter speed is especially important when trying to capture a moving subject like sports.

ISO: the final element in the exposure triangle is ISO, which stands for International Standards Organization. It is the industry’s standardized scale for measuring sensitivity to light. When shooting film, ISO is called film speed as each roll of 35 mm film is rated with a specific ISO. In the digital age, ISO measures how sensitive the camera’s digital image sensor is to light. ISO is usually adjusted when dealing with an extremely low light situation.

All three parts are used together when exposing a shot. A photographer would adjust any or all of these depending on the lighting conditions or the desired composition. So how do you know which to adjust when shooting? Good question.


(Mosaic was shot indoors at a subway station. Exif info: f4.5, 1/25 sec., ISO 400)

It takes time and experimentation to know which element of the exposure triangle to adjust in any given situation. The adjustments work in tandem. For instance, if a photographer uses a large aperture to get shallow depth of field (that nice blur in the background), then that means the photographer will be letting in a lot of light through the lens and can therefore use a faster shutter speed to reduce the amount of light let in by the shutter. In this scenario, the ISO would remain constant (ISO 100 is a usual baseline) as the exposure is being handled by adjustments to the aperture and shutter. Generally speaking, adjusting the ISO is only done in relatively difficult lighting conditions. Using an extremely high ISO can possibly result in a loss of clarity in the image and increased film grain/noise.

Knowing and understanding the exposure triangle is the first step to creating wonderful images. Next week, we will cover the rule of thirds.


Kim Jones has been in the photography universe for over 20 years. After taking a long break from photography, she is working her way back into the field by randomly walking the streets with a camera.