How to Use Aperture Priority Mode on Your Canon EOS 6D

By Doug Sahlin

If you like to photograph landscapes, Aperture Priority mode is right up your alley. When you take pictures with the Canon’s Aperture Priority mode, you choose the desired f-stop and the camera supplies the proper shutter speed to achieve a properly exposed image. A large aperture lets a lot of light into the camera, and a small aperture lets a small amount of light into the camera.

The benefit of shooting in Aperture Priority mode is that you have complete control over the depth of field. You also have access to all the other options, such as setting the ISO speed, choosing a picture style, changing the AF mode or Drive mode, and so on. To take pictures with Aperture Priority mode:

  1. Press the Mode Dial lock and rotate the Mode dial to Av (Aperture value).


  2. Press the ISO button and then rotate the Main dial to change the ISO speed to the desired setting.

    When choosing an ISO speed, choose the slowest speed for the available lighting conditions. For more information on changing ISO speed.

  3. Rotate the Main dial to select the desired f-stop.

    As you change the aperture, the camera calculates the proper shutter speed to achieve a properly exposed image. The change appears in the LCD panel and the viewfinder. As you rotate the dial, monitor the shutter speed in the viewfinder. If you notice that the shutter speed is too slow for a blur-free picture, you have to put the camera on a tripod or increase the ISO speed setting.

    If you see the minimum shutter speed (30 seconds) blinking, the image will be underexposed with the selected f-stop. If you see the maximum shutter speed (1/4000 second) blinking, the image will be overexposed with the selected f-stop.


  4. Press the Shutter button halfway to achieve focus.

    A green dot appears in the viewfinder when the camera achieves focus.

  5. Press the Shutter button fully to take the picture.

    The image appears on your LCD monitor almost immediately.

How to control depth of field

Depth of field determines how much of your image looks sharp and is in apparent focus in front of and behind your subject. When you’re taking pictures of landscapes on a bright sunny day, you want a depth of field that produces an image in which you can see the details for miles and miles.

Other times, you want to have a very shallow depth of field in which your subject is in sharp focus but the foreground and background are a pleasant out-of-focus blur. A shallow depth of field is ideal when you’re shooting a portrait.

You control the depth of field in an image by selecting the f-stop in Aperture Priority (Av) mode and letting the camera do the math to determine what shutter speed will yield a properly exposed image. You get a limited depth of field when using a small f-stop value (large aperture), which lets a lot of light into the camera. A fast lens:

  • Has an f-stop value of 2.8 or smaller

  • Gives you the capability to shoot in low-light conditions

  • Gives you a wonderfully shallow depth of field

When shooting at a lens’s smallest f-stop value, you’re letting the most light into the camera. The lens you use also determines how large the depth of field will be for a given f-stop. At the same f-stop, a wide-angle lens has a greater depth of field than a telephoto lens. When you’re photographing a landscape, a wide-angle lens and a small aperture is ideal.

When you’re shooting a portrait of someone, you want a shallow depth of field. Therefore a telephoto lens with a focal length that is the 35mm equivalent of 85mm with a large aperture (small f-stop value) is the ideal solution.


How to use depth-of-field preview

When you compose a scene through your viewfinder, the camera aperture is wide open, which means you have no idea how much depth of field you’ll have in the resulting image. You can preview the depth of field for a selected f-stop by pressing a button on your camera. To preview depth of field:

  1. Compose the picture and choose the desired f-stop in Aperture Priority (Av) mode.

  2. Press the Shutter button halfway to achieve focus.

    A green dot shines solid on the right side of the viewfinder when the camera focuses on your subject.

  3. Press the Depth-of-Field Preview button.

    The button is conveniently located on the right front side of the camera when your camera is pointed toward your subject. You can easily locate the button by feel. When you press the button, the image in the viewfinder may become dim, especially when you’re using a small aperture. The camera chooses the proper shutter speed to compensate for the f-stop you select.


    When you use depth-of-field preview, pay attention to how much of the image is in apparent focus in front of and behind your subject.