Aperture priority mode allows you to choose (set) the aperture size; whereas in automatic mode, the camera sets the aperture size. When you photograph the subject, the aperture will be fixed while the camera calculates the shutter speed and ISO for standard exposure. You can choose the ISO as well.
How to Use Aperture Priority Mode?
Aperture priority is usually abbreviated with an A on the camera mode dial. Canon cameras abbreviate it with Av.
To use aperture priority:
- Set the mode dial to aperture priority.
- Use the main dial to select the desired aperture size.
- Set the ISO if required.
- Take the photo.
It is best to refer to the camera’s manual.
When to Use Aperture Priority Mode?
Use aperture priority when you want a shallow or narrow depth of field but are unsure of the shutter speed or ISO. Or you don’t have time to balance the shutter speed or ISO because you only have an instance to photograph but you know what depth of field you want.
The below photos are an example of aperture priority. The left photo was set with an aperture of f/22 and right with f/2.8. Both photos focused on the middle bottle of coke with a tripod. The ISO was auto and the camera determined the shutter speed for standard exposure. Focal length was fixed at 24 mm. Ideally, it’s better to keep the ISO as low as possible to reduce noise. This is why choosing the ISO is important instead of allowing the camera. Look at the difference between the depths of fields.
High dynamic range photography requires aperture priority (or manual) mode. When you take bracketed photos, you need to have the same depth of field when merging the photos. Otherwise, the merged photo will be blurry.
If shooting handheld in low-light and the camera chose a slow shutter speed, then the image will be blurry. In this case use a flash, manual mode, or a tripod.