Canon 60d (37591)

How Aperture Priority Mode Affects Photos

You have been shooting for a few weeks with your new digital SLR and are ready to graduate from full automatic mode to get more creative control over your photos. It is time to step up to Aperture Priority Mode. This is the easiest advanced mode to learn that gives you more control of your final product, yet allows the camera to do a lot of the heavy lifting for you.

Aperture Priority Mode

First you need to place your camera in aperture priority mode. This is usually denoted on your dSLR mode dial with an A or an AV/Av. When you place your camera in this mode you allow the camera to take care of shutter speed and film speed (or ISO) while you control the aperture. These three items together determine how much light your camera needs to make a good exposure on a picture.

The aperture controls how much light enters the lens. The shutter speed controls how long that light is allowed to expose the film or sensor. The film speed (even though there is no film involved) controls how sensitive the sensor will be to the light that is allowed in by the other two factors.

When your camera is in aperture priority mode that means that you have control of the amount of light entering the camera on any given picture. The camera determines the shutter and film speeds automatically. Beyond the amount of light that enters the lens, the aperture effects how much of the image will be in focus from front to back. This is called depth of field.

The higher the aperture number, the smaller the opening. The easiest way to understand this is that the number is a fraction: 1/4 is larger than 1/22. An aperture with an f-stop of f/4 will allow 1/4 of all possible light that the lens could allow through it to the sensor. An f/16 setting will only allow 1/16 of all possible light to pass through.

There is another way to think about it which does not really explain what is happening in the lens, but it will help you understand the effects. That is to think about the fact that a larger aperture number gives you a greater depth of field. A smaller number gives you a smaller depth of field.

  • High number = small opening = less light = greater depth of field
  • Low number = large opening = more light = smaller depth of field

Using Aperture Priority Mode Creatively

The reason you want to use aperture priority mode is to take advantage of the creative depth of field that this mode allows. For large nature photography you want a large depth of field (larger aperture number) to give you as much of the picture in focus as possible. For personal close-up photography you want a narrow depth of field (smaller aperture number) to draw the viewer's eyes to your primary subject.

Here is a practical example of how you would use this. You want to shoot a picture of your child outside in the beautiful fall leaves. If your purpose is to show grandma how much fun grandson is having playing in the leaves you would want a greater depth of field (larger aperture number, but smaller aperture opening). This gives a crisp focus on the child and shows the backdrop of the leaves. However, if your purpose is to use the leaves as a colorful backdrop for a nice casual portrait of your child then you would use a narrow depth of field by choosing a smaller aperture number. By doing so you allow more light in to keep your child's face in focus, but put the leaves outside of the focus range. This draws the viewer's focus to the child and not the surrounding environment.

Experiment with Aperture Priority Mode

The beautiful thing about digital photography is that you can shoot as many pictures as you like and it won't cost you any more than shooting just a few. Set your camera in aperture priority mode and begin experimenting with how the mode affects your pictures. While you are experimenting you know that the camera will still have the proper exposure because it handles the shutter and film speeds automatically.

Aperture priority mode is the easiest and most creative way to start using your dSLR off of its fully automatic mode. There are certainly other modes that you can experiment with such as Shutter Priority Mode and Full Manual Mode. Those will come in time. For now experiment with aperture priority and how it helps you take more creative photos.

To see how the triad of aperture, shutter speed and film speed affect your pictures, you will be interested in my article where I explain aperture and shutter speed in detail.