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Home    Lesson Plans    #1: Understanding Exposure

Course Requirements

  1. Before starting this lesson, you should have a basic understanding and know how to operate your digital camera. If you are really new to photography with a new DSLR camera, I suggest you read up on the following articles first
  2. You must have a digital SLR camera or a digital camera that have the following functions:
    • Ability to set camera to Aperture Priority Mode setting
    • Ability to set camera to Shutter Priority Mode setting
    • Ability to set camera to Manual Mode setting
    • Ability to set camera to Program Mode setting
    • Ability to change the ISO setting on your camera
  3. Optional: A lens with a maximum aperture of f/2.8 or larger and minimum aperture of f/22 or smaller.

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What is Exposure?

In photography, Exposure is the total amount of light bouncing off a subject that is allowed to enter through an opening in the camera lens for a certain period of time until the light (image) is recorded onto the camera sensor. When you focus your camera to take a picture of a scene, the light that is reflected off the subject enters through an opening in the lens (aperture) and is allowed to pass through to the camera sensor for a certain amount of time (shutter speed). The amount of light that passes through the lens opening and the duration of the light needed for a proper exposure is dependent on how sensitive the camera sensor is to light (ISO). Digital SLR (DSLR) cameras are built with a light meter that is able to calculate the correct combination of aperture (lens opening), duration of time light is allowed to pass through the sensor (shutter speed) and the sensor's sensitivity to light (ISO). We will talk more about Light meters as we progress through this lesson.

  • Additional Reading! If you want to know more about how light enters your DSLR camera and how a photo is produced, read our What is a DSLR Camera? article. This article talks about what a DSLR camera is and how it works as well as its advantages over "point and shoot" digital cameras.

Below are examples of photographs at different levels of exposure.

Sample ExposuresFigure 1: Sample Exposures

The first photograph is an example of a overexposed photo where there was too much light captured by the camera. The middle photograph shows you a photo with the proper exposure which means that there was just enough light captured by the camera that rendered an ideal photo exposure. The third photo is an example of an underexposed photo where there was not enough light captured by the camera.

In this lesson, I will show you how you can get good exposure on your photographs. There are three elements that affect exposure. They are described below.

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Exposure Triangle: Aperture, Shutter Speed and ISO

Exposure Triangle
Figure 2: Exposure Triangle

In photography, there are 3 basic elements: Aperture, Shutter Speed, and ISO. These 3 elements are responsible for controlling a photograph's exposure. Mastering all 3 elements is an essential part of developing your skill in photography.

All digital cameras, and even film cameras, work the same way. Photographs are created by capturing light onto a light-sensitive medium which records the image. The 3 elements mentioned above, Aperture, Shutter Speed and ISO, capture light in different ways and together they control how a photograph is created or exposed.

Aperture: the size of the opening in the lens when a photo is taken. The opening controls how much light can enter your camera at once

Shutter speed: the amount of time that the shutter is open. This amount of time controls the amount of time that light is allowed to hit the sensor.

ISO: the sensitivity of the photographic medium to light. In film cameras, this refers to how sensitive the film is to light and in digital cameras it refers to how sensitive your camera's digital sensor is to light. More sensitivity to light means less light is needed for a good expose of a photograph.

These 3 elements are tightly related. A change in one of the elements will impact the other two. This means that each of the 3 elements are dependent on one another in order to come up with the correct exposure. Your camera has a light sensitivity level that is set by the ISO setting. To get the correct exposure, the lens opening need to be adjusted to control the volume of light entering the camera. Then the shutter is opened for a certain period of time to allow the light to hit the sensor and record the image. Coming up with the correct exposure means combining the right blend of aperture, shutter speed and ISO settings.

Let me begin by explaining Aperture first. At the end of the Aperture lesson, you will be given assignments so that you will be able to apply the knowledge and practice what you learned. I urge you to complete the assignments first before going on to the next lesson. Besides, it is more fun to be using your camera than it is to read a lesson, isn't it?

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