UNDERSTANDING EXPOSURE

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Home    Lesson Plans    #1: Understanding Exposure

What is Aperture

As stated in the previous page, Aperture is the opening in the lens when a photo is taken. The camera's aperture setting controls how much light can pass through your camera lens. The aperture settings are called f-stops and are represented by numbers (i.e. f/1.8, f/2, f/8, etc). The bigger the number, the smaller the lens opening. I know it can be confusing in the beginning but you'll get used to it over time. To see what I mean, refer to Figure 1 below. It shows you a picture of the lens opening in full stop increments from the largest (f/2) to the smallest (f/22). Notice how the highest f-stop number (f/22) has the smallest opening? Also, the largest opening has the lowest f-stop number (f/2). This is just one of the things you need to remember in photography. Don't worry if it is confusing at first, it will start to make sense as soon as you start using your camera and fiddling with the aperture settings.

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Lens Aperture Openings
FIGURE 1: Lens Opening - Aperture Setting
  • It's time to tinker with your camera! Take a few minutes and tinker with your camera's aperture settings. Get familiar with how to change the aperture settings on your camera. Consult your manual if you do not know how.

The images below shows illustrations of the effect of aperture on the exposure of the photo. The images shows shots using the largest lens opening to the smallest. In this example, the ISO and shutter speed remain constant to isolate the effect of aperture on the exposure of the photograph.

Effect of Aperture on Exposure
FIGURE 2: Effect of Aperture on Exposure

In the example photos above, the photo taken at F/5.6 has the correct exposure. Did you notice that the photos taken with wider aperture is overexposed and photos taken with smaller aperture is underexposed?

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Aperture and Depth of Field

Each of the 3 different elements of exposure has a unique effect on a photograph. The different effects are used by photographers to achieve certain creative goals of their photos. Aperture has the unique effect called Depth of Field.

Depth of Field is a measure of how far the field of focus is in a photograph. It is the amount of distance between the nearest and farthest objects that appear in sharp focus in a photo. The size of the aperture opening determines the depth of field, or how much of your scene is in focus. Lower f-stop number means less depth of field or shallow depth of field. When your aperture is wide open (smallest f-stop number), your focus will be much shallower and there will be fewer things in your photo that will be in focus. On the opposite end, higher f-stop number, which means smaller lens opening, will allow for a deeper focus which means that more things in your photo to be in focus.

The sample images below shows photos with different levels of depth of field.

Exposure 1
F/2.8, 1/100 sec, ISO 200
Exposure 2
F/5.6, 1/50 sec, ISO 200
Exposure 3
F/16, 1/6 sec, ISO 200

FIGURE 3: Depth of Field

Notice that the photo taken with the widest aperture (F/2.8) has the least of amount of area in the photo that is in focus. The only thing that is in sharp focus is the middle of the flower - the edges start to blur a little bit. The stem of the flower is also blurred. The background is blurred to the point that it is almost indistinguishable. The second photo taken at F/5.6 has more of the photo in focus. The flowers leaves is pretty much in sharp focus and the stem is more in focus than the first photo at F/2.8, and while the background is still blurred, it is distinguishable. The third photo taken at F/16 has the most area in focus of the 3 photos shown. The flower and its stem are in sharp focus and the background is only slightly blurred and it is clearly distinguishable as pink flowers.

Notice also that the shutter speed varies between the different photos in the above example. If more light is allowed to pass through the lens by choosing a larger aperture opening, the amount of time that the shutter is open should be shortened. If the shutter is allowed to stay opeen for a longer duration, the aperture needs to be adjusted to a smaller opening the restrick the amount of light coming into the lens. If you do not adjust the shutter speed to compensate, you will get the a darker image as you increase your f/stop. (See Figure 2: Effect of Aperture on Exposure above)

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Camera Setting: Aperture Priority Mode

Aperture Priority Mode Dials

Aperture Priority Mode is a setting on your camera that allows you to choose a specific aperture value while the camera selects a shutter speed to match. So all you need to worry about is selecting the aperture setting you like depending on how much focus or depth of field you need for your photo.

The Aperture Priority Mode is usually represented by an Av or an A on your camera dial. See illustration on your right. Consult your camera's product manual if you are unable to find the setting for Aperture Priority Mode.

  • It's time to tinker with your camera! This time, take a few minutes to figure out the Aperture Priority Mode setting on your camera. Become familiar with it and then set your camera to Aperture Priority Mode. Consult your manual if you do not know how.
  • Additional Reading! For more about Aperture and its real world uses, read our Aperture and Aperture Priority Mode article. This article talks about aperture priority mode in more detail than is discussed here.

Assignment 1.1: Get familiar with Aperture

For the rest of the week, I would like you to spend time getting familiar with Aperture. I want you play around with your camera, setting it to Aperture Priority Mode. Our goal for this assignment is to familiarize yourself with your camera's aperture settings and what kind of photos you produce using the different aperture settings. I want you to be able to distinguish between the different aperture settings through your photos. How much of your subject do you want to focus? A little? A lot? When you have determined how much focus you need, figure out what aperture setting you need to set to accomplish it. Experiment... discover... this is the only way to learn.

Assignment Instructions

  1. Set your camera to Aperture Priority Mode
  2. For this exercise, set your ISO to 400 (if you are outside during the daytime) or 1600 if you are inside your house with less lighting. Dont' worry about how I came up with that number, the ISO setting is not important in this exercise. Check your camera's manual if you do not know how to set the ISO.
  3. Find a subject, preferably a fixed subject (a subject that is not moving). For example, a toy, a flower, or anything you can find in your house or your backyard. I would recommend you do this exercise out in your backyard in the daytime so there is more light.
  4. Set your aperture to its widest opening, or set it to the smallest f/stop number. For example, one of my prime lenses goes all the way down to f/1.4.
  5. Take a picture of your fixed subject.
  6. Now, change your aperture setting to say, f/8 and take a picture of your subject again.
  7. Next, change your aperture setting to its smallest opening. In other words, set it to the highest f/stop number, for example, f/22. Take a photo of your subject again.
  8. Lastly, download your photo and view it on your computer. What's different about the 3 photos you took? How does the aperture setting affect the photo? Did you notice the difference in focus? Depth of field?

Project 365 or 52 Week Project for the serious hobbyist

If you are really serious about learning photography then I highly recommend that you try Project 365 or 52 Week Project. Both of these projects are great ways to practice and learn photography. For more detailed information about these projects and how to start, read my Project 365 or 52 Week Project blog. I have carefully organized a Weekly Theme Suggestions for this project to coincide perfectly with our step by step Lesson Plans.

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